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1
UDDER MORPHOLOGY AND EFFECTS ON MILK PRODUCTION AND EASE OF
MILKING IN DAIRY SHEEP
Maristela Rovai1, David L. Thomas2, Yves Berger3, and Gerardo Caja4
1Physiology Weihenstephan, Technical University Munich, D-85350 Freising,
Germany
2Department of Animal Science and 3Spooner Agricultural Research Station,
University of Wisconsin-Madison, 53706 Madison, USA
4Grup de Recerca en Remugants, Unitat de Producció Animal, Universitat
Autònoma de Barcelona, 08193 Bellaterra, Spain
Summary
Mammary morphology is generally accepted as a key factor for machine milkability,
and its inclusion in dairy sheep improvement programs has been widely recommended.
The anatomical and morphological characteristics of the mammary gland and their
relation with milk production, machine milkability and manageability in dairy sheep have
become of greater interest from farmers to researchers. The sheep udder is an exocrine
epithelial gland mainly constituted by tubulo-alveolar parenchyma with alveoli and well
differentiated cisterns. Two anatomical compartments are considered for milk storage:
alveolar and cisternal; the large-cisterned animals being more efficient milk producers.
The evaluation of external morphology by using udder typology, objective udder
measurements and linear scores in practice is also discussed. Recent methodology
using ultrasonography has been applied for the study of the mammary gland, providing
a satisfactory non-invasive method for determination of milk storage characteristics in
dairy species. Machine milkability is evaluated by milk fractioning and milk emission
curves during milking. Both criteria are discussed and analyzed in sheep breeds of
different milk yield. Relationship between morphological and productive traits in dairy
sheep is analyzed as a result of anatomical and physiological characteristics.
Phenotypic and genetic correlations indicate that selection for milk yield will produce
worse udder morphology, resulting in udders which are inadequate for machine milking,
especially in highly selected flocks. Teat and cistern characteristics appear to be the
most limiting factors in machine milkability. Some selection pressure on udder traits in
long-term breeding programs needs to be considered and the use of linear udder traits
is recommended in practice to improve udder morphology and milkability.
Knowledge of the relationship of udder morphology traits with milk production and
milking time in U.S. dairy ewes is needed to provide producers with recommendations
for culling strategies based on ewe udder traits. The effectiveness of the European
scoring systems for dairy-meat breeds cross ewes in U.S. dairy sheep farms is
discussed.
2
Introduction
The current breeding goal for milkability in dairy cows, goats and sheep is focusing
on an improvement of the adaptation of these animals to the machine milking process,
and its influence on milking time and farm economics. According to Labussiere (1988),
even if the main quality of a dairy ewe is its production level, it is essential to be able to
extract rapidly the milk retained in the udder, not only with a minimum of manual
interventions (udder stimulation, machine stripping and hand stripping), but also, at
times which are not too restricting and sufficiently spaced, to allow the practice of
omitting one milking per day (Sunday, end of lactation, etc.).
The interest in the dairy sheep udder has increased in the last few years when the
anatomy has been explored in depth (Ruberte et al., 1994b; Caja et al., 1999; Carretero
et al., 1999), and a linear scoring system has been developed to select udders with
good “milkability” in Spanish and Italian breeds (De la Fuente et al., 1996 and 1999;
Carta et al., 1999), as well as the evaluation of its genetic parameters (Gootwine et al.,
1980; Mavrogenis et al., 1988; Fernández et al., 1995; 1997; Carta et al., 1999).
Moreover, given the negative effects observed in udder morphology as a result of the
increase in milk yield, the main udder traits of breeds with different yields (Rovai et al.,
1999; Rovai et al., 2003a) or of genetically isolated lines of the same breed (Marie et al.,
1999) are under comparison.
Shape and size of the udder and teat have been shown to be related to milk yield
(Labussière et al., 1981; Labussière, 1988; Fernández et al., 1995, 1997; Carta et al.,
1999; Rovai et al., 1999) and milk flow rate (Marnet et al., 1999; Marie-Etancelin et al.,
2002) in Spanish and French dairy breeds. However, the repeatability and heritability of
udder morphology traits and their relationships with milk yield and milking time in U.S.
dairy ewes are needed so that recommendations can be given to producers on whether
or not udder morphology should be considered in culling and selection decisions. A
preliminary study of udder traits with U.S. dairy ewes was conducted by McKusick et al.
(1999) and continued with more detailed udder characterization by Rovai et al. (2003a).
The American dairy sheep industry started by milking breeds of sheep commonly
available in the U.S. and selected for lamb and wool production. Strict animal health
regulations on the importation of live sheep, ram semen, and sheep embryos was a
major obstacle to importations of genetic material from breeds of selected sheep from
other countries. However, due to the persistency of producers and some university
researchers, a small amount of genetic material in the form of semen and embryos of
two dairy sheep breeds (East Friesian of German origin and Lacaune of French origin)
was imported into Canada and the U.S. Since the dairy sheep industry is expanding at a
very satisfactory rate, there is a need for producers to continually strive to improve the
economically important traits of milk yield, milking time, and udder conformation in order
to produce sheep with better milking performance and reduced milking labor costs in the
future.
3
This paper describes the particularities of the dairy sheep udder and summarizes the
current implications of udder morphology on machine milkability. Some of the results
obtained on dairy-meat cross ewes under U.S. production conditions are also
presented.
Mammary Gland in the Dairy Ewe
The mammary gland is an exocrine epithelial gland, exclusive to mammal species,
which is quantitatively and qualitatively adapted to the individual growth requirements
and behavior of each species. It shows histological similarities to other epithelial glands
such as the salivary and sweat glands. Milk secretion is described as the activity of a
cellular factory (the lactocyte) which transforms itself into the product (the milk). The
entire process is controlled by integrated neuro-endocrine and autocrine systems. It
mainly develops during pregnancy and early lactation, and regresses very quickly after
dry-off. However, in pregnant ruminants this regression is limited.
Origin and development of the mammary gland: The mammary gland is formed
by two main structures: the parenchyma and the stroma. The partitioning between both
structures defines the anatomical and functional characteristics of each mammary
gland. The parenchyma is the secretory part of the gland and it is made up of tubulo-
alveolar epithelial tissue, coming from the ectoderm layer of the embryo, and it consists
of the tubular (ductal) and alveolar systems. The stroma is formed by other
complementary tissues of mesodermic origin such as: vessels (blood and lymph) and
different tissues (adipose, connective and nervous). Both structures develop very early
from the ventral skin of the embryo and half-way through the pregnancy, reaching a
total of eight pairs of isolated mammary buds in all mammal embryos (Delouis and
Richard, 1991).
At birth, the sheep udder shows clearly differentiated cisterns (Sinus lactiferus) and
teats (Papilla mammae) and very incipient development of the ductal system, with few
primary ducts surrounded by numerous stroma forming cells. After birth the udder grows
at the same rate as the body (isometric growth) until puberty, with proliferation and
branching of the secondary ductal system. Puberty in most species is the quickest
period of growth for ducts and stroma of the mammary gland (positive allometric
growth), as a result of the action of sexual hormones. Nevertheless, the future milk
capacity of the udder can be impaired at this stage by an excessive growth of the
stroma (mainly adipose and connective tissues) in comparison to the parenchyma
(tubulo-alveolar epithelium). This critical phase occurs earlier in sheep than in cattle,
with differences between breeds. Thus, the parenchyma growth ends in sheep before
puberty and, as a consequence, mammogenesis in sheep will be affected by nutrition
during and after the positive allometric growth phase (Bocquier and Guillouet, 1990).
The critical period for mammogenesis is from 2 to 4 months old. Moreover an early
onset of puberty will bring forward the decrease in mammary development. According to
Johnson and Hart (1985) and McCann et al. (1989), a relative low growth rate (50% of
high rate) from weaning (wk 4) to the end of rearing period (wk 20) will increase the
parenchyma growth and the milk production in the first lactation in non-dairy ewe lambs.
4
No negative effects were observed at the beginning of puberty. Nevertheless a low
growth rate before weaning will also negatively affect mammogenesis (McCann et al.,
1989). Unfortunately there is no detailed information available on dairy sheep, but
Bocquier and Guillouet (1990) reported that the restriction of concentrate in Lacaune
ewe lambs, after they reach approximately 28 to 30 kg, increases milk yield by 10% in
the first lactation.
During the first and subsequent pregnancies, the parenchyma shows an allometric
growth where the placenta plays an important role producing a specific ovine chorionic
somatotropin hormone after day 60 of pregnancy, which is dependent on prolificacy.
Mammogenesis starts clearly in sheep between day 95 and 100 of pregnancy, with
detection of lactose (start of lactogenesis) after day 100 (Martal and Chene, 1993).
The presence of secretory lobes with alveolus in the extremes of the ducts can be
observed in the second half of pregnancy. Delouis and Richard (1991) estimate a
change from 10 to 90% in the relative weight of the parenchyma during pregnancy,
where the lobulo-alveolar development of epithelial cells takes the place of the adipose
tissue. The inverse process occurs during the dry period, with a complete
disappearance of the alveoli in the ewe after 3 to 4 weeks, and its replacement by
adipocytes (Hurley, 1989). Moreover during the involution process the mammary gland
is invaded by macrophages and lymphocytes, the latter being essential for the
production of immunoglobulins in the synthesis of colostrum in the next pregnancy.
Internal structure of the mammary gland: The internal structure of the ewe udder
reveals the presence of two independent mammary glands under a unique skin bag,
each of them wrapped by a bag of fibroelastic connective tissue (Apparatus
suspensorius mammarum) and separated by a clearly defined and intermediate wall of
connective tissue (Ligamentum suspensoris uber; Turner et al., 1952; Barone, 1978;
Tenev and Rusev, 1989; Ruberte et al., 1994b). The strength of this ligament normally
produces the presence of an intermmamary groove (Sulcus intermammarius) between
each gland which plays an important role maintaining the udder tightly attached to the
ventral abdominal wall. Each half udder shows internally a typical tubulo-alveolar
structure with a big cistern (Sinus lactiferus) divided in two parts: glandular cistern (S. l.
pars glandularis) and teat cistern (S. l. pars papillaris). Both cisterns are separated by a
muscular sphincter of smooth muscular fibers, traditionally known as the cricoid fold,
important for the milk drainage. It also helps to keep the teat and gland morphology
divided during machine milking to avoid the appearance of cluster climbing. The cricoid
sphincter is normally missing in goats and it is not very effective in the conic teat
udders, which are not favorable for machine milking. Size and form of the gland cistern
vary according to the breed and milking ability of the sheep, being greater and
plurilocular in high yielding ewes (Figure 1). Another sphincter with smooth muscular
fibers is present around the streakcanal (Ductus papilaris) in the distal part of the teat,
connected to the exterior by a unique orifice (Ostium papilare).
The last mammary gland structures in the parenchyma are the secretory lobes,
consisting of much branched intralobular ducts and alveoli. The alveolus is the secretory
5
unit of the mammary gland and consists of a bag of a unique layer of specialized cubic
epithelial cells (the lactocytes) with an inside cavity (the lumen) in which the milk is
stored after secretion.
The mammary gland stores the milk extracellulary and this storage can be explained
using a model of two anatomical compartments (Wilde et al., 1996): ‘Alveolar milk’
(secreted milk stored within the lumen of alveolar tissue) and ‘Cisternal milk’ (milk
drained from the alveoli and stored within the large ducts, the gland cistern and teat
cisterns). Short-term autocrine inhibition of milk secretion in the mammary gland has
been related to cisternal size, the large-cisterned animals being in general more efficient
producers of milk and more tolerant to long milking intervals and simplified milking
routines (Wilde et al., 1996).
The external morphology and anatomic ultrastructure of the mammary gland with its
canalicular system are shown in detail in the Figure 1.
6
Figure 1. Dairy sheep mammary gland. A) Dairy ewe udder; B) Cistern ultrasound; C)
Sheep udder anatomy (Rubert et al., 1994a); D) Microscopy images from
epoxy casts (Carretero et al., 1999) of: 1, lobular duct (L) and alveoli (*), 2,
collapsed alveolus, 3, alveoli, 4, intussusceptive growth in a lobular duct, 5,
alveolar sprouts; E) Cast of a dairy sheep udder obtained by the epoxy injection
and corrosion method (left) and detail of the ductal system with ducts and
alveoli (right; Carretero et al., 1999).
L
Gland cistern
Lobular
duct
Alveolo
teat
2
Gland cistern
Parenchyma
A
A
B
C
D
E
L
3
4
1
5
7
Morphology of the Mammary Gland
The anatomy and morphology of the sheep udder has been well known for many
years (Turner, 1952; Barone, 1978), and selection on udder morphology has been
assayed. Early works on the relationship between udder characteristics and milking
performance in dairy ewes were carried out in the 70’s and early 80’s (Sagi and Morag,
1974; Jatsh and Sagi, 1978; Gootwine et al., 1980; Labussière et al., 1981) as a
consequence of the efforts to adapt the ewe to machine milking.
With this aim, an international protocol (M4 FAO project) for dairy sheep udder
evaluation in the Mediterranean breeds was performed as an initiative from Prof.
Jacques Labussière (Labussière, 1983 and 1988). Based on this standardized protocol,
the udder of many dairy sheep breeds was systematically studied in relation to machine
milking (Casu et al., 1983; Fernández et al., 1983a; Gallego et al., 1983a;
Hatziminaoglou et al., 1983; Labussière et al., 1983; Pérez et al., 1983; Purroy and
Martín, 1983) and following symposiums in Europe (Arranz et al., 1989; Kukovics and
Nagy, 1989; Rovai et al., 1999), and also in America (Fernández et al., 1999b;
McKusick et al., 1999; Rovai et al., 2003abc).
According to Labussière (1988), the milk production is always correlated to size of
the udder, however, voluminous cistern cavities to assure the accumulation of the milk
secreted over long milking intervals and teats implanted vertically (at the lowest point of
the cistern) should be also considered to improve the milkability of dairy sheep.
Udder typology: Mammary morphology has been described as an important factor
in the machine milkability of dairy ewes (Labussière et al., 1981; Gallego et al., 1983a;
Fernández et al., 1995). The first practical utilization of udder morphology on dairy
sheep was made by using tables of udder typology in Awassi and Assaf (Sagi and
Morag, 1974; Jatsch and Sagi, 1978), Sarda (Casu et al., 1983) and Manchega ewes
(Gallego et al., 1983a, 1985), all of them based on four main udder types. These
typologies were later adapted to the Latxa breed (Arranz et al., 1989) and Hungarian
Merino and Pleven (Kukovics and Nagy, 1989). A comparative table of these typologies
can be observed in Figure 2. The typology used in Sarda was evaluated in field
conditions (Casu et al., 1989) and extended to seven udder types mainly based on teat
position and cistern size (Carta et al., 1999) with the aim of improving the small
discriminating capacity of the previous typologies (Figure 2). Typology is recommended
as a useful tool for the screening of animals, i.e. in the standardization of machine
milking groups or in the choice of ewes at the constitution or acquisition of a flock, and
for culling of breeding animals (Gallego et al., 1985; Carta et al., 1999). The evaluation
of sheep udders by udder types is easy, quick and repeatable with trained operators
(Carta et al., 1999; De la Fuente et al., 1999). However, the inclusion of non-subjective
measurements and linear evaluation needs to be considered for the study of machine
milkability of the dairy ewes.
Average milk production tends to be superior in Type I (horizontal teats) udders
probably due to the negative relation between milk production and teat insertion (Rovai,
2001). On the other hand, Type IV showed an inferior milk yield due to the unshaped
8
udder presented by the ewes in this category (Gallego et al., 1983a; Rovai, 2001). Most
of the time, ewes assigned to Type IV refers to animals with mastitis, field accidents,
etc.
The udder typology proposed by Gallego et al. (1983a) was evaluated in U.S. ewes
of dairy-meat crosses (Table 1) and compared with previous studies on other breeds
(Table 2). This system was designed to classify the ewes more adapted to machine
milking using teat angle insertion, and is based on visual examination and assignment
of udders into four categories (Figure 2): Type I = horizontal teats; Type II = teats at 45
degrees; Type III = vertical teats – most desirable (“udder machine”); Type IV =
misshaped udder. Also the presence or lack of presence of the suspensor ligament in
the udder was determined (1: yes and 0: no).
Figure 2. Udder scoring method proposed for different dairy sheep breeds (Peris, 1994,
modified).
I
II
III
IV
I
II
III
IV
IV
-
I
+ I
III
IV
-
II
+ II
IV
III
II
I
II
I
III
IV
V
Horizontal teats
and
Higher udder cisterns
VI
VII
III
IV
V
I
II
Moderate cistern
height
Null cistern
height
Vertical
teats
Unshaped
udders
Sarda
Casu et al.
(1983)
Latxa
Arranz et al.
(1989)
Sarda
Carta et al.
(1999)
Breed
UDDER TYPES
Awassi & Assaf
Sagi & Morag
(1974)
Awassi & Assaf
Jatsh & Sagi
(1978)
Manchega
Gallego et al.
(1983)
9
Table 1. Udder typology and the presence or not of the suspensor ligament (IG) in
commercial and university U.S. dairy-cross ewes.
Udder type (%)
IG (%)
Flock1
Ewe crosses n I II III IV
1 0
A EF (10 to 50%) 166
6
(4%) 123
(74%) 29
(17%) 8
(5%)
166
(100%) 0
B EF (10 to 75%) 177
19
(11%) 113
(64%) 32
(18%) 13
(7%)
167
(94%) 10
(6%)
C 194
27
(14%) 132
(68%) 28
(14%) 7
(4%)
189
(97%) 5
(3%)
D1 EF (75%)
EF (50%)
LC (50%)
EF-LC (¼ EF– ½ LC)
27
48
26
18
5
(18%)
10
(21%)
13
(50%)
5
(28%)
21
(78%)
36
(75%)
12
(46%)
13
(72%)
1
(4%)
1
(2%)
1
(4%)
0
0
1
(2%)
0
0
20
(74%)
38
(79%)
26
(100%)
5
(28%)
7
(26%)
10
(21%)
0
13
(72%)
A, B, C are commercial U.S dairy fams, and D is a University farm.
1 Measurements done at wk 11 of lactation.
As shown in Table 1, udders of Type II were more frequent than other types in all
flocks. Commercial-D flock also had a high percentage of ewes with udders of Type I
which may be the result of the presence of Lacaune ewes. Its response is reasonable to
expect when in France, the Lacaune breed has been efficiently selected on milk yield,
and this has a negative correlation with udder traits. These results are in agreement to
Rovai (2001) where comparing 232 ewes of Manchega and Lacaune breeds, a similar
frequency of Type II udders was found in both breeds, as shown in Table 2. However,
Manchega breed showed a higher incidence of Type III (more adapted to machine
milking), whereas Lacaune dairy sheep presented a larger percentage of Type I udders,
with teats placed more horizontally. The incidence of Type IV, which implies a worse
milkability, was very low due to the culling of these ewes in this flock.
Table 2. Udder typology from different sheep breeds.
Udder type (%)
Ewe breeds I II III IV
Authors
Manchega 19.2%
56.2% 14.3% 10.3%
Gallego et al. 1983a
11.6%
52.2% 2.9% 33.3%
Fernández (1985)
8.6%
75.0% 13.6% 2.8%
Rovai, 2001
Lacaune 15.7%
71.6% 8.7% 4.0%
Rovai, 2001
24.5%
67.9% 7.4% 0.2%
Rovai, 20011
1 A purebreed Lacaune flock from the experimental research station “Lafage”,
Roquefort (France).
10
The frequency of udder types (mainly Type I) tend to increase according to the age
of the ewe, although it seems not to be affected by the state of lactation (Rovai, 2001).
An ideal proposal would be to assess udder morphology during the first lactation, and
allow only those ewes with udders adapted to machine milking to remain in the herd.
Some examples of udders from U.S. dairy-cross ewes are shown in Figure 3. As we
can observe, the udders can be easily classified into the described udder typology.
Figure 3. Examples of types of udders from commercial and university U.S. dairy-cross
ewes classified according the typology proposed by Gallego et al. (1983a).
TYPE 1
TYPE 2
TYPE 3
TYPE 4
11
Udder measurements: The use of objective measurements for the characterization
of the dairy sheep udder and its relations with other productive traits has been
undertaken by different authors. The importance of the mammary traits on milk yield
and milking routine has been studied in the dairy ewe since the development of
machine milking, and its evaluation during lactation can be significant for obtaining a
positive genetic response in the milkability of dairy ewes. Until now, the mammary traits
have not been considered as a primary objective in dairy sheep selection. Nevertheless,
these traits determine several aspects of the machine milking and manageability (time
of milking, falling off of the clusters, difficulty of lambs to find the teats,...).
The continuous nature of the measurements increases the discriminating capacity of
each variable and the significance of the correlation with the productive traits. The
methodology generally used corresponds to the standardized protocol of Labussière
(1983) with small variations incorporated in some cases (Gallego et al., 1983a;
Fernández et al., 1983a, 1995; Rovai, 2001).
Udder size (depth, width, length, and circumference), teat size (length and width),
teat angle, and cistern height are measured in vivo using a ruler and protractor as
shown in Figure 4. The main traits which can be grouped and which explain an
important amount of the variability of the mammary morphological traits are: 1) Udder
size: height, depth and width; 2) Teat size: length and width; 3) Teat insertion angle and
cistern height.
The repeatability of udder measurements made according to this methodology is low
for udder dimensions (r= 0.17 to 0.18), medium for teat dimensions and teat position (r=
0.45 to 0.52), and high for teat angle (r= 0.65) and cistern height (r= 0.77), as calculated
by Fernández et al. (1995) in the Churra dairy breed.
Figure 4. Mammary traits, rear and lateral view.
C: udder circumference, a: teat angle, W: udder width, H: udder depth,
h: cistern height, l and w: length and width of the teat and D: udder depth.
H
h
w
l
C
a
D
W
12
Udder shape and size is related to milk yield and milking time in specialized dairy
sheep breeds in Europe (Gallego et al., 1983a; Fernández et al., 1983b and 1995;
Rovai, 2001). The comparison of main udder measurements among dairy-meat cross
ewes under U.S. production conditions was also studied, and are in accordance with
previous studies on different breeds of ewes. Table 3 shows that milk yield and udder
traits were different between U.S. dairy-cross ewes.
Milk yield was highest in East Friesian-Lacaune ewes, increased with age of ewe,
and decreased through lactation. Lacaune ewes had the shortest teats and the highest
teat insertion. Cistern height and udder size were larger in Lacaune and East Friesian-
Lacaune ewes than in the other two breed groups and corresponded with their greater
milk production. Udder size and teat size increased with parity number, reaching their
maximum in ewes of three or more lactations. Udder size decreased through lactation
while teat angle and cistern height increased.
In general, the stage of lactation produced significant effects on all udder traits in
accordance with previous studies on udder morphology. Udder traits increased
according to parity, and the maximum was observed on third and more parity ewes,
however, age effects only showed a tendency in teat angle and cistern height. These
results agree with those obtained previously in different breeds (Labussière, 1988;
Fernández et al., 1983a, 1995; Casu et al., 1983; Gallego et al., 1983a; Labussière et
al., 1983; Fernández et al., 1989a, 1995; Rovai, 2001).
Table 3. Mean values of udder traits and effects of breed in U.S. dairy-cross ewes (Rovai
et al., 2003a).
a,b,c Within sheep group per trait, values with a different superscript are different
(P < 0.05).
Analysing the results on Table 3, we can also observe that the different cross-breeds
ewes present enough differences in udder morphology to be grouped according to
Ewes crosses
Traits EE (¾ EF)
EF (½ EF)
LC (½ LC) EF-LC (¼EF-½LC)
Ewes n 27 49 26 18
Milk yield liters 1.3 a 1.2 a 1.2 a 1.6 b
Udder size
depth cm 8.8 a 8.7 a 9.1 a 10.3 b
width cm 13.8 a 13.5 a 14.0 ab 14.7 b
length cm 21.2 a 21.2 a 21.8 ab 23.1 b
circumference
cm 42.5 a 42.2 a 43.4 a 46.7 b
Teat size
length cm 3.3 a 3.4 a 3.0 b 3.4 a
width cm 1.5 a 1.5 a 1.4 b 1.5 a
Teat angle degrees
48 a 51 c 59 b 54 c
Cistern height cm 3.0 a 3.3 a 3.8 b 4.0 b
13
udder type, making the possibility of establishing a universal udder classification valid
for all breeds almost impossible.
In regard to the correlation coefficients between udder traits, three natural groups
can be distinguished as indicated by Fernández et al. (1995): 1) udder size (height and
width), which are high and positive; 2) teat size (width and length), which are medium
and positive; and 3) cistern height and teat placement (position and angle) which are
medium and positive but show low and negative correlation with teat and udder sizes.
As udder width increases, cistern height and teat angle decrease; and, as udder height
increases, cistern height and teat angle also increase.
When morphological traits are related to milk yield, the greatest effects are observed
for udder width and height and tendencies are only observed for the remaining traits
(Gallego et al., 1983a; Labussière et al., 1983; Fernández et al., 1989a, 1995; McKusick
et al., 1999; Rovai et al., 2003a). Big volumed and cisterned udders produce more milk.
Main effects of teat traits are related to milk fat (McKusick et al., 1999) and milk
emission during milking (Fernández et al., 1989a; Marie et al., 1999).
As a conclusion, the most significant and repeatable udder traits agreed by different
authors for a wide sample of sheep dairy breeds are:
- Teat dimensions (length) and placement (angle)
- Udder height and width
- Cisterns height
Linear scores: The main drawback of the udder typologies is their use for the
estimation of the genetic value of breeding animals when genetic and environment
effects need to be considered for selection. This problem has been solved in dairy
sheep, as in dairy cows and goats, by using a breakdown system in which independent
udder traits are based on a 9-point scale per trait as shown in Table 4 (De la Fuente et
al., 1996).
The system is based on the following udder traits: udder depth (from the perineal
insertion to the bottom of the udder cistern), teat angle (teat insertion angle with the
vertical), and teat length (from the gland insertion to the tip), and also includes an
expanded typology to evaluate the whole udder shape, in accordance with the
previously described optimal criteria for udder types. Each udder trait is evaluated
independently by using extreme biological standards.
The desirable value is in some cases the highest score (i.e. teat angle: vertical teats
that scored 9 will reduce cluster drops and will make easier the milk drainage) or the
average score in others (i.e. teat length: medium size teats scored 5 and agree with a
uniform cluster length). In udder height, given its positive relationship with milk
production an average score will also be preferable. This linear methodology has been
used in Spain for the evaluation of different flocks of Churra, Manchega and Latxa dairy
ewes (De la Fuente et al., 1999; Serrano et al., 2002), partially in France for Lacaune
breed (Marie et al., 1999), and in U.S. for the evaluation of the machine milking ability of
East Friesian and Lacaune crossbred ewes (Rovai et al., 2003b/c).
14
Table 4. Linear scores for the evaluation of main udder morphological traits in dairy
sheep (De la Fuente et al., 1999).
Morphological trait Score (1 to 9)
1 (Shallow) 5 (Average) 9 (Deep)
Udder depth or height
1 (Horizontal) 5 (45 degrees) 9 (Vertical)
Teat angle
1 (Short) 5 (Average) 9 (Long)
Teat length
1 (Faulty) 5 (Average) 9 (Ideal)
Udder shape
The linear udder scoring systems evaluated in U.S. included flocks of dairy-meat
ewe crosses from three commercial dairy sheep farms and one university farm, as
shown in Table 5. Percentage of East Friesian breeding had no effect on udder trait
scores in the commercial farms. However, Lacaune ewes from the University farm had
the most horizontal teats, according to their morphological descriptive traits discussed
previously. As we can observe in Table 5, Lacaune crosses tended to have udders less
suited to machine milking compared to East Friesien crosses; as assessed by the
European scoring systems.
Udder depth score increased significantly as parity number increased in all farms,
reaching the maximum values in third and greater lactations. Udder depth score
decreased through lactation in the commercial farms, and remained constant in the
15
3
4
5
6
0 1 2 3 4 5 6 7
Lactation number
Score
3
4
5
6
01234567
Lactation stage (month)
Score
University flock. Ewes in later stages of lactation tended to have more horizontal teats
and faulty udders than ewes in earlier stages of lactation. Within all genotypes and
farms, positive and significant correlations were observed between udder depth scores
and milk yield (0.20 to 0.46). High correlations were observed also between udder
shape and teat angle scores (0.80 to 0.93), and also between udder depth score and
milk production.
Table 5. Linear udder scores in U.S. dairy-cross ewes farms (Rovai et al., 2003b).
Traits
Flock Farm Ewe crosses n Udder depth
Teat angle
Udder
shape
n
A commercial EF (10 to 50%) 177 4.4 4.9 5.0
B commercial EF (10 to 75%) 166 4.6 5.3 5.5
C commercial 197 3.8 5.2 5.1
D university EF (50 or 75%)
LC (50%)
EF-LC (¼ EF– ½ LC)
120 5.1a
5.3 a
6.0 b
4.3 a
3.3 b
3.9 a
3.8
3.1
3.7
a,b Within farm C, values with a different superscript are different (P < .05).
The results obtained for Spanish breeds, according to lactation stage and parity
effects, are shown in Figure 5. In regard to lactation stage, all linear scores decreased
as lactation progressed, udder height and udder attachment being the traits which
showed the greatest decrease during lactation, while teat size was only slightly
modified. This evolution agrees with the loss of udder volume and milk yield but
indicates a deterioration of udder morphology for machine milking as indicated by udder
shape. Only udder height was improved. Regarding lactation number, udder height
increased dramatically in the first lactations, while other traits decreased, and teat size
was steadily constant. As a consequence, udder shape deteriorated, and its score
decreased rapidly from first to third lactation and stabilized thereafter.
Figure 5. Evolution of linear scores of main udder traits in Spanish dairy sheep: ?,
udder height; ¦, udder attachment; ?, teat angle; ?, teat length; and, ?, udder
shape (elaborated from De la Fuente et al., 1999).
16
The values of linear scores calculated by Fernández et al. (1997) in the Churra dairy
breed (Table 6) were sufficiently repeatable (r= 0.48 to 0.64) and showed intermediate
heritability values (h2=0.16 to 0.24) as reported in cattle. Coefficients of variation ranged
between 18 and 37%. Nevertheless udder shape showed high and positive genetic
correlation with udder attachment (r= 0.55) and teat placement (r= 0.96), as a result of
the main role of these traits in the definition of udder shape. On the other hand, udder
shape was highly repeatable and heritable, indicating its utility as a single trait for dairy
sheep selection. Consequently, the use of the first four linear udder traits will be
sufficient to improve programs of udder morphology. Phenotypic and genetic
correlations showed that selection for milk yield will produce worse udder morphology,
mainly in udder height and teat placement, giving as a result baggy udders which are
inadequate for machine milking. Authors indicate that a single scoring per lactation
would be sufficient in practice.
Table 6. Genetic parameters of linear udder traits in dairy sheep (Fernández et al.,
1997). Correlation with milk yield Trait Heritability
(h2) Repeatability
(r) Phenotypic (rp)
Genetic (rg)
Udder height
Udder attachment
Teat placement
Teat size
Udder shape
0.16
0.17
0.24
0.18
0.24
0.51
0.48
0.64
0.54
0.62
0.40
−0.01
−0.04
0.03
0.03
0.82
−0.02
−0.34
−0.16
−0.26
Repeatabilities of udder linear scores obtained in Lacaune dairy breed (Marie et al.,
1999) were also high (r= 0.59 to 0.71) and show amoderate phenotypic correlation with
milk yield in primiparous and multiparous ewes. Heritabilities of udder traits reported in
Assaf (h2= 0.23 to 0.42; Gootwine et al., 1980), Chios (h2= 0.50 to 0.83; Mavrogenis et
al., 1988), and Sarda with the seven expanded typologies (h2= 0.55; Carta et al., 1999),
gave higher values but, as indicated by the last authors, probably they were
overestimated. Serrano et al. (2002) also reported the importance of the udder depth as
an intermediate optimum trait for machine milkability, due its high genetic correlation
with milk yield. Nevertheless, taking into account the conclusions of Fernández et al.
(1997) and Serrano et al. (2002), the genetic variability and heritability of the studied
udder traits indicates that the efficiency of the breeding programs could be improved,
and some selection pressure on udder traits in long-term breeding programs needs to
be considered. The utilization of a selection index including udder depth in selection
programs, in order to increase the milkability of dairy sheep is also recommended
(Serrano et al. (2002).
According to the sheep milk working group from ICAR (world-wide organization for
the standardization of animal recording and productivity evaluation), more and more
country members are interested in udder morphology related to milking ability, mainly at
an experimental level. Udder scores have been carried out in Cyprus, France,
Germany, Italy, Spain and Switzerland. Some countries such as France, Spain and Italy
aim to include the scores in selection criteria.
17
Use of digital pictures to study udder morphology. Practical application of the
digital system for evaluation of mammary morphology may provide an easy and
accurate method to study ewe udders. Advantages of the digital picture method are that
pictures can be taken faster than the in vivo measurements at the farm, analyzed at
your convenience, and it can provide a permanent record for future use.
To evaluate the effectiveness of this method, the relationship between udder traits
measured in vivo and from digital photographs were studied on 120 U.S. dairy-cross
ewes from a University farm (Rovai et al., 2003c). Digital pictures were taken in the
milking parlor of the rear udder of each ewe at the time of the in vivo measurements
(objective measurements and linear score system). A ruler, as each picture was taken,
was held parallel to the ground in the same vertical plane as the back of the udder and
a few cm below the bottom of the udder to serve as a calibration device for
measurements on the digital pictures (Figure 6). Likewise a plumb bob was suspended
vertically in back and in the middle of the udder while taking each picture to give a true
vertical line as a reference for measuring teat angle. Measurements from the digital
pictures were obtained using the public domain software, Image Tool from Texas
University, available on the Internet.
Figure 6. Examples of udder digital pictures.
Comparisons of the in vivo and digital measurements are presented in Table 7. In
general, udder traits in vivo did not differ statistically nor substantially from the digital
pictures measurements. Teat length was the only trait that differed between methods;
perhaps due to folding at the teat udder junction, which is not visible in the
measurements taken from the pictures.
All digital measurements were significantly correlated with those measured in vivo.
Phenotypic correlations between the methods (direct udder measurements and
measurements from pictures) were: 0.73 for udder height, 0.67 for udder width, 0.47 for
teat length, 0.88 for teat angle, 0.68 for teat size score, 0.79 for teat angle score, 0.88
for udder height score, and 0.89 for udder shape score. The major ewe udder traits that
18
can be viewed from the rear can be accurately measured from digital photographs of
the rear udder.
A similar technique of image analysis was conducted by Marie-Etancelin et al.
(2002). These authors confirmed, by sufficient repeatabilities and positive correlations
with scores, the feasibility and objectivity of this technique through the extraction of the
original udder measurements. However, due to the special conditions of the method
(people and equipment as artificial lights, metric standard, black panels to show up the
contrast and camera), and analysis techniques (special software for the extraction and
calculation of the measurements from a digital picture), at the moment of its application,
would be possible only at an experimental level.
Table 7. Udder measurements taken in vivo and from digital pictures.
Ultrasonography and milk production capacity: Size of the cisterns is related to
morphology and yielding capacity of the udder, varying markedly with time from last
milking. Apparently, short-term autocrine inhibition of milk secretion in the mammary
gland has been related to cisternal size; the large-cisterned animals being in general
more efficient producers of milk and more tolerant to long milking intervals and
simplified milking routines (Wilde et al., 1996). Machine milkability can be modified by
cistern features, however, there is a low relationship found between cistern size and
milk yield (Gallego et al., 1983a; Labussière et al., 1981; Fernandez et al., 1995), due
probably to the method used on its evaluation (external measuremnets). Cistern is a
non visible internal udder structure, and its size together with all other udder traits have
been measured externally using a ruler and protractor in the past. Recent literature
describe the use of ultrasound technique for estimating the size of udder cisterns.
Ultrasonography has been used as a non invasive method to study the internal
structure of the mammary gland in cows (Bruckmaier and Blum, 1992; Bruckmaier et
al., 1994; Ayadi et al., 2003a), sheep (Caja et al., 1999; Nuda et al., 2000; Rovai et al.,
2000 and 2003a) and goats (Salama et al., 2004) and to measure the milk storage
capacity within the udder (Ayadi et al., 2004; Caja et al., 2004). The principle structures
of the mammary gland, as cistern area and teat cistern, can easily be determined by the
Measurements
Traits in vivo picture
Udder
measurements
Udder depth cm 21.8 19.3
Udder width cm 13.9 12.9
Teat length cm 3.3a 2.2 b
Teat angle degrees 52.6 52.8
Udder linear score
Udder depth 1-9 5.4 5.3
Udder shape 1-9 3.6 3.6
Teat length 1-9 5.3 5.6
Teat angle 1-9 3.9 3.8
19
position and frequency of the transducer used for its exploration. In dairy sheep, a
specific method for mammography was proposed by Ruberte et al. (1994a), with the
transducer applied and directed from the portion of the proximal intermammary groove,
between areas of superficial inguinal lymph nodes, towards the teat. The method can
also be used to estimate the distribution and movement of milk between the udder
compartments and for non-invasive dynamic studies on cisternal milk.
Differences in cisternal area according to dairy species and dairy sheep breed are
summarized in Figure 7.
Figure 7. Cistern ultrasound scans in dairy cows (A, Ayadi et al., 2003; B, Rovai et al.
2004), dairy goats (C; Bruckmaier y Blum, 1992), and different breeds of dairy ewe (D).
Udder cisterns filled with milk appear as dark areas, and the glandular parenchyma
appear as a gray-white areas.
Lacaune
East Friesian-Lacaune East Friesian (¾ EF )
East Friesian
(
½
EF
)
Lacaune crossbred
Manchega
20
The differences in cistern capacity according to the productive level of two different
dairy breeds were evaluated by Rovai et al. (2002). In this study, Lacaune ewes showed
a larger area of the mammary cistern and also a larger amount of cisternal milk when
compared to Manchega ewes (24cm2 and 275ml vs. 14cm2 and 149ml, respectively).
Lactation number did not affect cisternal area. However, this area, as well as the
amount of stored milk, decreased through the lactation in both breeds.
The breed differences on cistern storage capacity was also studied among dairy-
meat cross ewes under U.S. production conditions (Rovai et al., 2003a). Cistern area
was different between ewe crosses as shown in Table 8.
East Friesian (¾ crosses) and East Friesian-Lacaune dairy ewes had greater cistern
area than ewes of the other two breeds (East Friesian, ½ crosses; Lacaune ewes).
Cistern area and milk yield in this study, decreased throughout lactation and increased
with parity. In contrast, Bruckmaier et al. (1997) reported no differences in cistern area
in Lacaune and Friesian dairy ewes. In general, cisternal areas and cisternal milk show
high dependency. Significant correlations between cisternal areas and milk production,
udder size measurements, and, in a lower extent, teat measurements were also
reported.
The use of cistern ultrasonography in dairy cows showed that losses in total milk
yield is negatively related with cisternal milk volume (r=-0.77) and cisternal size (r=-
0.70), meaning smaller losses in big udders in response to omitting one milking weekly
(Ayadi et al., 2003a). Recent studies also suggest that udder anatomy (mainly size of
mammary cisterns) in terms of milk storage may be an important factor in determining
reduced yield associated with extended milking intervals in dairy species (Knight and
Debwhurst, 1994; Stelwagen et al., 1996; Davis et al., 1998; Ayadi et al., 2003a;
Salama et al., 2003). Regarding this subject, the omission of one or more milkings per
week in dairy ewes as well as dairy goats (eg. Sunday afternoon) would provide an
important improvement in the quality of life of farmers, especially in small or family
based dairy farms.
New studies on mammary gland: The most recent studies on the mammary gland
related to morphology refer to the identification of quantitative trait loci affecting udder
traits in dairy sheep (Casu et al., 2003). Casu et al. (2003) have been working on QTL
detection with the hypothesis of the presence of different alleles controlling udder
morphology on a population of F1 crossbred Lacaune and Sarda ewes (Carta et al.,
2002). Several QTL affecting udder morphology traits were detected for the first time
through methods consisting of extracting objective measurements from digital pictures
and repeated udder scoring.
C
D
21
Table 8. Cistern area by ultrasonography, average milk production, and relation
between scan area and cistern milk according to dairy species and the ultrasound
scanner used (AMP, average milk production; Area, cistern area).
Dairy species AMP Area
(cm2)
Cistern
milk×Area
Array
scanner
(MHz) Reference
Dairy cows
Simmental×Holstein
26 kg/d 28 - 5.0
linear Bruckmaier et al., 19921
Holstein 20 l/d 3-41 0.84-0.88 5.0
sectorial
Ayadi et al., 2003
Buffalo
Murrah 50-3202 26-70
0.87 6.0 linear Thomas et al., 2004
Dairy goats
Swiss Saanen 3.5 kg/d 16 - 5.0
linear Bruckmaier et al., 19921
Murciano-granadina
1.1 l/d5 13-28
0.72 5.0
sectorial
Salama et al., 2004
Dairy sheep
East Friesian (EF)
EF crossbred
EF (½ EF)
EE (¾ EF)
EF-LC (¼EF-½LC)
Lacaune crossbred
LC (½ LC)
Lacaune
Manchega
Sarda
3.2 kg/d
0.81-1.19kg
1.2 l/d
1.3 l/d
1.6 l/d
1.2 l/d
0.67-1.34kg
1.7 l/d
0.9 l/d
92 to 1562
19
40
27
30
32
24
33
1.7 l/d
13
19
-
-
0.71
0.76
0.73
0.64 -
0.50
0.82
0.82
5.0
5.0
3.5
3.5
3.5
3.5
5.0
5.0
5.0
3.5
linear
linear
sectorial
sectorial
sectorial
sectorial
linear
sectorial
sectorial
linear
Bruckmaier et al., 19921
Bruckmaier et al., 1997
Rovai et al.4
Rovai et al. 4
Rovai et al. 4
Rovai et al. 4
Bruckmaier et al., 1997
Rovai, 2001
Rovai, 2001
Nudda et al., 2000
Meat Sheep 1.62 l/d 5.6 0.90 5.0
sectorial
Caja et al., 1999
1 Five animals from each group to study the effect of exogenous oxytocin on gland and
teat cistern. Values shown correspond to the gland cistern before oxytocin treatment.
2 These values correspond to the cisternal yield (ml).
3 The lower value of correlation for Lacaune ewes can be probably explained by the
capacity limitations of visualization using a 5MHz ultrasound transducer.
4 Unpublished data.
5 Values from half udders.
Machine Milkability in the Dairy Ewe
Milk partitioning in the udder (cistern and alveolar fraction), milk fractions collected
during milking (e.g., machine milking and machine stripping), residual milk (e.g.,
obtained after oxytocin injection) and milk flow curves during machine milking have
been used to evaluate machine milkability in dairy sheep (Labussière, 1988; Bruckmaier
22
et al., 1997a; Marie-Etancelin et al., 2002; Rovai, 2001; Díaz et al., 2004). The
methodology proposed in the M4 FAO Project (Labussière, 1983) is normally used as
the standardized method for both criteria.
Milk partitioning in the udder: Milk partitioning between cisternal and alveolar
compartments may influence milk secretion and milk yield response to altered milking
frequencies (Knight et al., 1994; Ayadi et al., 2003a; Salama et al., 2004). Large
differences between species and breeds exist with regard to the proportion of total milk
that can be stored within the cisternal compartment (Bruckmaier et al., 1992; Ayadi et
al., 2003a; Salama et al., 2004). In sheep, high variation in cisternal milk has been
reported with values ranging from less than 30% for meat breeds (Caja et al., 1999) to
more than 50% for dairy breeds (Nuda et al., 2000; Rovai et al., 2000; McKusick et al.,
2002), showing that selection for milk yield resulted in larger cisternal udders to
accommodate the greater milk volumes.
Nevertheless cisternal milk volume can be increased in some breeds by
spontaneous liberation of endogenous oxytocin as a consequence of milking
conditioned behavior or during udder manipulation. This can be avoided by using
oxytocin antagonists to temporarily block spontaneous milk letdown, as reported in
cows (Bruckmaier et al, 1997a; Wellnitz et al., 1999; Ayadi et al, 2003), ewes (Rovai et
al., 2000; McKusick et al., 2002) and goats (Knight et al., 1994; Salama et al., 2004).
Milk partitioning between the udder compartments (cisternal and alveolar) was
determined in two different dairy sheep breeds, under the same production system, by
Rovai et al. (2000) using an oxytocin receptor blocking agent as shown in Table 9.
Table 9. Milk partitioning in the udder of dairy ewes according to the breed and the use
of Atosiban as an oxytocin blocking agent (Rovai et al., 2000).
Manchega Lacaune Effect (P < )
Item Control
Atosiban2
Contr Atosiban
SEM Breed Atosiban
Ewes
Milk yield1
Milk partitioning
Cisternal
Alveolar
Total
Cisternal: Alveolar
Cisternal area
n
L/d
ml
ml
ml
%
cm2
10
0.94
122
86
208
59:41
12.4
10
-
118
104
222
53:47
13.1
10
2.07
299
89
388
77:23
24.0
10
-
239
115
354
68:32
23.2
-
0.10
79
0.63
1.06
-
0.90
-
0.001
0.001
0.712
0.010
0.001
0.001
-
-
0.001
0.001
0.465
0.001
0.961
1 Average udder milk yield and composition during the experimental period (90 DIM).
` 2 Oxytocin receptors blocking agent injected in jugular
As shown in Table 9, despite the differences in milk production (over 100%) at the
same stage of lactation, alveolar milk was very similar in the two breeds, the difference
being only 10% greater in Lacaune ewe. On the contrary, the difference in true cisternal
23
milk was 102% greater according to the difference observed in yield. These differences
suggest that the volume of cisternal milk is the only difference between Lacaune and
Manchega breed and highlight the important role that cistern size plays in the milk yield
of the dairy sheep.
Similarly, percentage milk fractions differed significantly according to breed, with
superiority of cisternal fraction in Lacaune ewes, and consequently a greater
percentage of alveolar milk in Manchega ewes. These results clearly support the
interbreed changes due to selection programs schemes increasing the milk yield and
consequently cisternal area of selected dairy sheep.
Carretero et al. (1999) studying the ultrastructure of the mammary gland in
Manchega and Lacaune ewes reported the same mammary structures and pattern of
development during lactation, describing an equally and extensive proliferation of the
canicular system with a large number of alveolar sprouts between week 1 (suckling) and
5 (start of milking) in both breeds.
The observed better milkability of Lacaune ewes can be explained by the progress in
breeding for improved milk production which also provided animals with quiet
temperament at the milking parlor, more spontaneous milk ejection reflex and
improvement of the dairy sheep management without the need of a previous udder
preparation as used for dairy cows.
In resume, the use of an oxytocin receptor blocking agent is potentially a convenient
method to determine with exactitude the amounts of cisternal and alveolar milk
fractions, under normal conditions of milking (Knight et al., 1994). However, as
observed in Table 9, the volume of milk fractions according to treatment tended to be
different between breeds. The fractions were similar and accurate for Manchega ewes
while the Lacaune presented a spontaneous milk ejection when entering to the milking
parlor. From this study, conclusions suggest the necessity to use an oxytocin antagonist
when we need to prevent the milk ejection and analyze the fractions of milk separately
in well know adapted machine milking breed.
Milk fractioning during milking: Milk fractions were mainly used as an important
indicator for the evaluation of the milkability in dairy sheep when the routines included
hand stripping reported by the M4 FAO project (Labussière, 1983). Reported values of
milk fractioning varied according to breed (Labussière, 1988; Such et al., 1999a),
milking routine (Molina et al., 1989) and machine milking parameters (Fernández et al.,
1999a). Values of fractioning ranged normally from 60 to 75 : 10 to 20 : 10 to 15, for
machine milking : machine stripping : residual milk, respectively.
The comparison of milking ability of two groups of ewes characterized by different
milk yield (Manchega, 0.6 l/d; Lacaune, 1.3 l/d), was carried out by Such et al. (1999a)
in late lactation (week 16) and under the same milking conditions. Values of fractional
milking (machine milk : machine stripping milk : residual milk) were 65:19:16 and
68:21:11, for Manchega and Lacaune ewes, respectively. No significant differences
were observed according to breed in percentages of milk fractions, except in the case of
24
residual milk (Figure 8). Both breeds gave on average 86% milk during machine milking,
but Manchega breed retained more milk in the ductal system of the udder. This result
was obtained despite the differences reported in milk yield and in absolute values of
each fraction, as well as in cistern size and udder morphology, of each breed as
discussed previously. Differences in udder size and morphology explain the increase in
machine stripping milk according to milk yield, and were also reported by effect of
lactation stage (Gallego et al., 1983b; Labussière, 1988).
As a conclusion, the obtained results show the unsuitability of the milk fractions as a
main indicator for the evaluation of milkability in ewes, fractioning probably being a
better indicator for the study of machine or milking routine effects, which were the same
in this case. Moreover, Caja et al. (1999a) in the goat and Fernández et al. (1999a) in
sheep, reported significant differences in the machine stripping fraction according to
milking routine or machine milking parameters, respectively.
Figure 8. Milk fractioning obtained during machine milking of dairy sheep
according to the breed at the same stage of lactation (Such et al., 1999a): MM,
machine milk; MSM, machine stripping milk; RM, residual milk; m, milked; g,
present in the gland.
A study comparing the effect of stripping or its omission on milk production in dairy
ewes was conducted by McKusick et al. (2003). This study, based on data from 48
multiparous East Friesian crossbred dairy ewes, suggested that overmilking would not
occur when stripping is omitted from the milking routine and the lack of machine
stripping could result in a approximately 14% reduction in the commercial milk.
Moreover, residual milk does not have a negative influence on milk quality.
Udder morphology traits and milking fractions do not seem to be related (Rovai,
2001).
NS
NS
NS
NS P< 0.05
0
20
40
60
80
100
MMm MSMm MMg MSMg RMg
Milking fraction
Volume (% total)
Manchega
Lacaune
25
Milk emission: Milk emission is one of the most interesting criteria for studying
milkability in the machine milking of dairy sheep, and its main traits are considered to be
relevant for the design of milking machines and to adopt the optimal milking routine in
each breed. As milk yield strongly influences intramammary pressure, a strong effect of
milk production on all milk flow parameters is also expected, as indicated by Marnet et
al. (1999) and observed clearly in dairy goats (Bruckmaier et al., 1994; Caja et al.,
1999a). Moreover, milk emission will be different for a.m. and p.m. milkings, and its
curves should be analyzed separately. Morning milking will increase milk flow and
milking time, however emission of alveolar milk will be observed easily and separately in
the afternoon.
Milk emission curves are obtained by manual (Labussière, 1983; Fernández et al.,
1989b; Peris et al., 1996; Rovai, 2001) or automatic methods (Labussière and Martinet,
1964; Mayer et al., 1989b; Bruckmaier et al., 1992; Marie et al., 1999). The flow from
the right and left mammary glands can be recorded separately (Labussière and
Martinet, 1964; Labussière, 1983) or as a whole (Fernández et al., 1989b; Peris et al.,
1996; Bruckmaier et al., 1992 and 1997; Marie et al., 1999; Marnet et al., 1999), but
results and conclusions of flow may be different in consequence (Rovai, 2001).
A good milk emission curve should mean a quick and complete milking, with a high
milk flow rate and an effective ejection of alveolar milk under the action of oxytocin. The
milk emission pattern is related to the structure of the udder (cistern size), to the teat
traits (size and position) and to the neuro-hormonal behavior of the ewe (Labussière et
al., 1969; Bruckmaier et al., 1994, 1997; Marnet et al., 1998, 1999). Globose and big
cisterned udders with medium size, vertical and sensitive teats, that are able to open
the sphincter rapidly and widely at low vacuums, are preferable.
An early typology of milk emission curves was proposed by Labussière and Martinet
(1964), and widely adopted for the study of sheep dairy breeds (Labussière, 1983,
1988). The milk emission typology considers curves of different shape: ‘1 peak’ (single),
‘2 peaks’ (bimodal) and others, the last corresponding to animals with irregular or
multiple milk emission curves (≥ 3 peaks or “plateau”). In some cases there are changes
in the milk emission typology on consecutive days, and more than two recordings are
recommended in practice. The first peak occurs very early after cluster attachment, and
it is identified as cisternal milk, which is drained after the opening of the teat sphincter.
The second peak corresponds to alveolar milk and occurs as a consequence of
liberation of alveolar milk during the appearance of the milk ejection reflex by effect of
released oxytocin (Labussière and Martinet, 1964; Labussière et al., 1969; Fernández
et al., 1989b; Marnet et al., 1998). The “plateau” type curves or those with more than 3
peaks usually presented a larger volume of milk, time of onset of the first peak, and total
time of emission when compared with curves of “2 peaks” (Rovai, 2001).
Milking-related release of oxytocin has been measured in dairy sheep by Mayer et
al. (1989a), Marnet et al. (1998), Bruckmaier et al. (1997) and Negrao and Marnet
(2003). Bruckmaier et al. (1997), in Lacaune and Friesian dairy ewes, demonstrated
different oxytocin release between both breeds. Lacaune ewes presented a dramatic
increase in blood concentration during teat stimulation and early milking, while only
26
slight release was found in Friesian ewes. Theses differences were marked during
machine milking with a significant increase in oxytocin observed in 88% of Lacaune
ewes and only 58% of Friesian ewes. The authors also indicate the occurrence of single
peak typologies in milk emission with or without increasing concentrations of oxytocin in
both breeds. The decline in machine milking efficiency is more related with the decrease
in milk yield throughout lactation than with the oxytocin release, which remains constant
even after drying off (Marnet and McKusick, 2001).
The machine milk fraction is normally greater and milk flow maintained high during a
longer time in the bimodal ewes, which are considered favorable for machine milking in
dairy ewes. Milking of ewes showing a single milk emission curve can be completed by
using a milking routine including machine or manual stripping (‘repasse’) after cessation
of the machine milk flow, increasing dramatically the total milking time per ewe.
Moreover, simplified milking routines (without hand or machine stripping) are well
accepted by bimodal ewes as indicated by Molina et al. (1989) in Manchega dairy
sheep. Distribution of animals in a flock according to number of peaks has also been
used as an index of machine milkability in dairy breed as indicated by Labussière
(1988). Sheep breeds with a greater percentage of ewes showing 2 peaks being the
most appropriate for machine milking. Nevertheless peak distribution in a flock changes
according to the stage of lactation as observed by Rovai (2001) in a flock with breeds of
different yield and milkability (Table 10). Number of ewes in the 1 peak group increased
at the end of lactation and on the contrary the ≥ 3 peaks decreased.
Table 10. Distribution (%) of milk emission curves obtained in dairy ewes during
machine milking according to breed and stage of lactation in (Rovai, 2000).
Manchega Lacaune Stage of
lactation
(d) 1 peak 2 peaks ≥ 3 peaks 1 peak 2 peaks ≥ 3 peaks
421 28.6
(62)2 56.7
(123) 14.7
(32) 8.0
(16) 57.2
(115) 34.8
(70)
70 29.6
(67) 64.2
(145) 6.19
(14) 9.8
(25) 49.4
(126) 40.8
(104)
98 39.4
(74) 54.8
(103) 5.9
(11) 18.0
(34) 55.6
(105) 26.5
(50)
1: First week after weaning at day 35.
2: Number of emission curves analyzed.
Results in Table 10 showed the most frequent emission curve between both breed
was with 2 peaks. The Lacaune breed also showed a higher percentage of ewes with
emission curves “in plateau” (more than 2 peaks), confirmed by their higher milkability.
Machine milking parameters can also modify the milk flow characteristics in dairy
sheep, mainly the volume of the second peak and the milking time, as reported by
Fernández et al. (1999a) in Manchega dairy ewes milked at different vacuum levels (36
and 42 kPa) and pulsation rates (120 and 180 P/min). The milking routine can also
affect milk flow as reported by Bruckmaier et al. (1997). These authors demonstrated
27
that the use of a prestimulation routine failed to reduce stripping milk and total milking
time but increased milk flow in Lacaune and Friesian ewes.
Clear differences in milk emission curves during the p.m. milking were observed by
Such et al. (1999b) according to breed, when Manchega and Lacaune dairy ewes at the
same stage of lactation were compared (Figure 9) indicating the importance of this
criterion on the evaluation of milkability. Daily milk yield at comparison and percentage
of bimodal ewes during the comparison period were 0.6 l/d and 38%, and 1.3 l/d and
83%, for Manchega and Lacaune ewes respectively.
Figure 9. Milk emission curves resulting from p.m. machine milking of dairy sheep
according to breed (?, Manchega; ?, Lacaune) and number of peaks (Such et al., 1999b).
Significant differences in the values of maximum milk flow (76 vs 129 ml/5s) and milk
peak volume (207 vs 586 ml) were observed for the 1 peak Manchega versus Lacaune
ewes, respectively. The significant values for the 2 peaks ewes were: first peak (72 vs
94 ml/s; and, 171 vs 344 ml) and second peak (41 vs 83 ml/s; and, 78 vs 239 ml), for
Manchega vs Lacaune, respectively. Total emission time until a milk flow <10ml/s were:
1 peak (25 vs 39 s) and 2 peaks (48 vs 56 s) for Manchega vs Lacaune respectively,
with the difference significant in all cases. Observed differences in milk flow parameters
between breeds were in accordance with their milk yield. Nevertheless, despite the
differences of milk emission curves, the total volume of milk obtained in 1 peak vs 2
peaks ewes were similar in each breed: Manchega (207 vs 249 ml) and Lacaune (586
vs 583 ml) respectively for 1 vs 2 peaks. Moreover maximum milk flow was the same in
both breeds for the 2 peaks ewes, despite the differences in yield. As a consequence, it
can be suggested that other factors different from milk ejection reflex are mainly
conditioning the milk flow during machine milking in dairy ewes.
1 peak 2 peaks
0
20
40
60
80
100
0 10 20 30 40 50 60 70
Time (s)
Flow rate (ml/5s)
0
20
40
60
80
100
0 10 20 30 40 50 60 70
Time (s)
Flow rate (ml/5s)
28
At present teat and cistern characteristics seem to be the most important factors in
relation to milk flow curves in dairy sheep. Results of Marie et al. (1999) and Marnet et
al. (1999) in Lacaune dairy sheep, and Bruckmaier et al. (1994, 1997) studying the
effects of milking with or without prestimulation in Saanen dairy goat, and Friesian and
Lacaune dairy sheep, are in accordance with these conclusions.
Marnet et al. (1999) indicate that lag time between teat cup attachment and arrival of
the first milk jets to the recording jar can be used as an indicator of milkability. Moreover
significant cornrelation of lag time with vacuum needed to open the teat sphincter (r=
0.61), total milking time (r= 0.86), and mean (r= –0.84) and maximum (r= –0.80) milk
flow rates, were observed. A low but significant correlation between Somatic Cell Count
and maximum milk flow was also obtained (r= 0.39). Moreover, the vacuum value
needed to open the teat sphincter seems to remain constant in each animal during
lactation and is also positively related with the teat congestion observed after milking.
The highest vacuum value needed to open the teat sphincter in this experiment was 36
kPa, suggesting that the use of a low milking vacuum is possible in Lacaune dairy ewes.
In accordance with these results, Marie et al. (1999) studied the main udder traits
and milk flow characteristics by using an automatic milk recorder in two lines of Lacaune
dairy ewes differing 60 l in genetic merit. Milk yield and milking time averaged 0.94 l/d
and 2 min 44 s respectively. Average lag time was 25 s for a minimum volume of milk of
160 ml. Maximum milk flow (0.87 l/min) was observed 27 s later (52 s from cluster
attachment) on average. Lag time was negatively correlated with milk yield (r= –0.26)
and maximum milk flow (r= –0.49). Measured repeatabilites for milk yield, lag time and
maximum milk flow were high in the same lactation (r= 0.46 to 0.59) and between
lactations (r= 0.40 to 0.75). Flow parameters varied according to milk yield as previously
reported by Bruckmaier et al. (1994) in goats, but the increase in milking time was lower
than in milk.
Marie-Etancelin et al. (2002) using two experimental flocks, a backcross population
of Sarda × Lacaune and a purebreed Lacaune, reported best values of milk emission
parameters (total milking time and milk flow) for the crossbred ewes compared with
Lacaune, which reflect the better milking aptitude of the Sarda breed. Values for milk
yield were only 4% higher for Lacaune breed; however the backcross population
showed short latency time (time needed to collect 160 ml of milk after the teat cup
attachment) and also time to reach the maximum milk flow (13s vs 28s for crossbred
and Lacaune ewes, respectively).
Similar studies were conducted in an experimental flock of U.S. dairy-cross ewes.
The milking emission parameters recorded during machine milking are shown in Table
10. Milk yield volume was highest in East Friesian-Lacaune crossbred ewes according
to their high milk production. Total milking time was also greatest in East Friesian-
Lacaune ewes, increasing with parity, and decreasing during lactation. Volume at the
first minute of milking was similar for ewe crosses regardless of different blood
percentages. The volume of milk during the first minute of milking can assure the
presence of alveolar milk ejection and milkability of these crossbred ewes. According to
29
Bruckmaier et al. (1997), milk flow curves with diffuse shape and peak flow rate below
0.4 kg/min represent extremely weak or totally absent oxytocin release.
In contrast, Bruckmaier et al. (1997) demonstrated that, despite similar milk yield
and cisternal areas in Lacaune and Friesian dairy ewes, milk flow was lower and
stripping milk yield higher in the Friesian ewes as a consequence of udder morphology
that showed cisternal bags below the level of the teat channel.
Positive relationships were observed between milking kinetics and udder traits (r =
0.15 to 0.38), and also between milk volume during the 1st minute and cisternal area (r =
0.34). Correlation of udder traits with flow parameters obtained by Marie et al. (1999)
were low (–0.3 to 0.3) and tended to increase in multiparous ewes. An increase in teat
angle was associated with a greater lag time (r= 0.28) and a lower maximum milk flow
(r= –0.26), both unfavorable traits. On the contrary, a very marked intermammary
groove was correlated with greater milk yield (r= 0.28) and milk flows (r= 0.33 to 0.34),
and lower lag time (r= –0.23). As a final conclusion the authors indicate that a good
udder shape tends to improve milkability in dairy sheep and recommended the inclusion
of this trait in genetic programs.
Table 10. Milking characteristics in U.S. dairy-cross ewes (Rovai et al., 2003).
Ewes crosses
Trait
EE
(¾ EF)
SEM
EF
(½ EF)
SEM
LC
(½ LC)
SEM
EF-LC
(¼EF-½LC)
SEM
Ewes
n 27
49
26
18
Milk yield
liters
1.25 a
0.06
1.24 a
0.05
1.20 a
0.06
1.59 b 0.08
Lag time
s 2.16 0.19
2.24 0.15
2.12 0.20
2.25 0.24
Volume 1st minute
liters
0.46 0.03
0.49 0.02
0.47 0.03
0.56 0.04
Volume without
liters
0.63 a
0.03
0.62 a
0.03
0.63 a
0.04
0.87 b 0.04
Total volume
liters
0.78 a
0.29
0.77 a
0.24
0.78 a
0.32
1.06 b 0.38
Time without stripping
s 1.26 a
0.09
1.21 a
0.07
1.31 a
0.09
1.61 b 0.11
Total time
s 1.63 a
0.12
1.61 a
0.09
1.75 a
0.13
2.13 b 0.15
Average flow rate
liters
0.45 0.02
0.42 0.02
0.44 0.02
0.48 0.03
New studies on milkability: New research focusing on genetic determinism of
milkability with regard to udder health and milking labour efficiency has been done at
INRA in France by Marie-Etancelin et al. (2002) in an experimental flock of Lacaune
ewes. Their results show that basic parameters of milk kinetics such as lag time or
maximum milk flow were relevant criteria for milkability classification with high
heritabilities and favourable genetic correlations with milk yield. These authors conclude
that a global udder index which allows improving both udder health and milkability with
an acceptable loss of the rate of genetic gain on milk traits is needed.
30
Summary and Implications
Information collected during this paper shows that to improve milkability, a well
shaped and healthy udder of dairy sheep should have:
- Great volume and globosely shaped
- Teats of medium size (length and width), implanted near to vertical
- Soft and elastic tissues, with palpable gland cisterns inside
- Moderate height, not surpassing the hock
- Marked intermammary ligament
Relationship between morphological and productive traits is evident in dairy sheep
as a consequence of anatomical and physiological characteristics. Phenotypic and
genetic correlations indicate that selection for milk yield will produce worse udder
morphology, mainly in udder height and teat placement, causing baggy udders which
are inadequate for machine milking. Teat and cistern characteristics appear to be the
most limiting factors in machine milkability and especially in milk flow. Genetic
variability, repeatability and heritability of udder traits indicate that some selection
pressure on udder traits needs to be considered. In practice the use of four linear udder
traits will be sufficient to improve udder morphology in long-term breeding programs.
Udder typology is a useful tool for quick screening of dairy sheep either at their
acquisition or in their culling. Linear udder scoring, equivalent to a typology of expanded
categories (nine), is a valid method for scoring ewes’ udders with practical application
on large scale. Its use would improve farmer’s management systems and economic
benefits, due to the culling of less productive ewes. However, due to the mammary
morphological differences presented between breeds, an individual linear score system
is need.
Breed differences are also detected despite the differences in milk yield, and values
of milk partitioning are in accordance with the known milkability of each dairy sheep
breed; the most productive ewes showing a larger machine milk fraction. The
differences in cisternal fraction of milk reported on different dairy sheep breeds explain
the different mammary gland anatomy and morphology among breeds and also among
selected ewes.
Mammary ultrasonography is an efficient method to evaluate the size and the
productive capacity of the ovine udder (highly correlated with milk production). This
method seems to indicate that cisternal size is a direct limiting factor for milk secretion
in dairy sheep and its importance is greater than the amount of secretory tissue.
Preliminary results on U.S. dairy-cross ewes show a superior milk production of East
Friesian-Lacaune crossing ewes, due probably to their bigger cisternal milk storage
area. The Lacaune breed resulted in poorer udder confirmation (larger teat angle,
greater external cisterns).
31
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