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Clinical mastitis in Spanish dairy cows: Incidence and costs

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Clinical mastitis in Spanish dairy herds has been studied. Since April 2005 up to December 2006, in 25 Spanish herds 1,054 cases registered were available. Aims were to determine mastitis incidence and factors of risk, to analyze whether yield production has been affected, and to quantify mastitis costs along 2006. The 25% lactations were infected at least once with average recurrence of 1.64. Descriptive analysis showed that 29% of cases occurred within the first month after calving. Primiparous showed higher mastitis frequency at early and late lactation while in multiparous cases number was progressively decreasing since the first month. Multiparous were statistically more liable to mastitis than primiparous. Mastitis did not show effect on yield production. Mastitis costs included treatment products and discarded milk. Individual daily production at each case onset was estimated by using monthly official milking records. An average mastitis case cost was 73.93 €, cheaper in primiparous than in multiparous because of lower milk production. Average discarded milk represented 74% of total cost per case. Mastitis costs were 117 € per infected cow and lactation. Then, annual economic losses due to mastitis were 3,190 € per average herd, showing the concern of producers on selecting resistant animals as well as the importance of the implementation of systematic recording for clinical mastitis in Spanish dairy farms.
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Instituto Nacional de Investigación y Tecnología Agraria y Alimentación (INIA) Spanish Journal of Agricultural Research 2008 6(4), 615-622
Available online at www.inia.es/sjar ISSN: 1695-971-X
Clinical mastitis in Spanish dairy cows: incidence and costs
M. A. Pérez-Cabal*, S. Yaici and R. Alenda
Departamento de Producción Animal. E.T.S.I. Agrónomos. Universidad Politécnica de Madrid.
Ciudad Universitaria s/n. 28040 Madrid-Spain.
Abstract
Clinical mastitis in Spanish dairy herds has been studied. Since April 2005 up to December 2006, in 25 Spanish herds
1,054 cases registered were available. Aims were to determine mastitis incidence and factors of risk, to analyze whether
yield production has been affected, and to quantify mastitis costs along 2006. The 25% lactations were infected at least
once with average recurrence of 1.64. Descriptive analysis showed that 29% of cases occurred within the first month after
calving. Primiparous showed higher mastitis frequency at early and late lactation while in multiparous cases number was
progressively decreasing since the first month. Multiparous were statistically more liable to mastitis than primiparous. Mas-
titis did not show effect on yield production. Mastitis costs included treatment products and discarded milk. Individual
daily production at each case onset was estimated by using monthly official milking records. An average mastitis case cost
was 73.93 , cheaper in primiparous than in multiparous because of lower milk production. Average discarded milk repre-
sented 74% of total cost per case. Mastitis costs were 117 per infected cow and lactation. Then, annual economic losses
due to mastitis were 3,190 per average herd, showing the concern of producers on selecting resistant animals as well as
the importance of the implementation of systematic recording for clinical mastitis in Spanish dairy farms.
Additional key words: genetic selection, udder health.
Resumen
Mamitis clínica en el vacuno lechero español: incidencia y costes
Se ha estudiado la mamitis clínica en 25 explotaciones utilizando 1.054 casos registrados desde abril de 2005 a diciem-
bre de 2006. Los objetivos del trabajo fueron determinar la incidencia, analizar si la producción se vio afectada y calcular
los costes generados en el año 2006. El 25% de las lactaciones presentaron algún episodio de mamitis, siendo la recurren-
cia media de 1,64. El 29% de los primeros casos se diagnosticaron en el primer mes tras el parto. Las primíparas fueron
más susceptibles al principio y al final de la lactación, mientras que las multíparas presentaron menos casos según avan-
zaba la lactación. Sólo resultaron estadísticamente significativos el rebaño y el número de lactación, siendo las vacas con
más de un parto más propensas a la mamitis. La producción de leche no se vio afectada. Los costes de mamitis incluyeron
los correspondientes a medicamentos y a la leche retirada no comercializada. La producción individual diaria en el momen-
to de la infección fue estimada utilizando el control lechero mensual oficial. El coste medio de mamitis fue de 73,93 ,
siendo más caro en las multíparas debido a una mayor producción. El coste medio por media de leche retirada representó
el 74% del coste por caso. El coste por vaca infectada fue de 117 por lactación, lo que supone unas pérdidas económi-
cas anuales por rebaño medio de 3.190 , justificando la preocupación de los productores por seleccionar animales resis-
tentes y la necesidad de sistematizar la recogida de mamitis clínicas en las explotaciones lechera españolas.
Palabras clave adicionales: salud de la ubre, selección genética.
Abbreviations used: AFRIGI (Asociación de Frisona de Girona), A.R. (autonomous region), DISC (discarded milk costs), EFRIFE
(Federación Frisona de Euskadi), TREAT (treatment administration costs), UPM (Universidad Politécnica de Madrid).
* Corresponding author: ma.perezcabal@upm.es
Received: 14-02-08. Accepted: 24-07-08.
Introduction
Breeding goal in dairy cattle is maximizing profita-
bility by selecting animals with high production that
remain as much time as possible in herd avoiding pro-
blems (i.e. functional animals). However, functionality
has been endangered through years because of exhaus-
tive selection on increasing production level and antago-
nistic genetic correlations between production and
resistance to some diseases (Rauw et al., 1998). Then,
nowadays profitability depends on reducing costs more
than increasing income (by improving production) and
selection is focusing on functional traits, such as ferti-
lity, diseases and calving ease (Philipsson and Lindhe,
2003; Stott et al., 2005).
The National Monitoring Health System (2007)
reported clinical mastitis, lameness, and infertility as
the most prevalent diseases. Moreover, mastitis has been
described as the most common and costly disease in
dairy production causing over 38% economic losses due
to health problems (Seegers et al., 2003). Mastitis fre-
quency increased dramatically in the last decades.
Heringstad et al. (1999) found that mastitis incidence in
1994 (28%) was two-times the frequency in 1978. In the
last ten years, depending on populations and lactation
number, averages ranged from 12% to 40% (i.e. Zwald
et al., 2004a; Wolfová et al., 2006). Risk factors asso-
ciated to clinical mastitis are milking routine, type of
housing, feeding, and season, as environmental effects
(Rupp, 1999). But also older cows, later first calving,
first stages of lactation, and cows with deep udders,
week attachments, and high production, are more liable
to mastitis (Carlén et al., 2004).
Health problems have negative consequences not
only on animal welfare (Collard et al., 2000) but also in
economics of herds because of additional costs in vete-
rinary, medicines, reduction of production, discarded
milk, and involuntary culling. Thus, economic losses
due to mastitis are an important concern for dairy pro-
ducers though some costs are not obvious (Østeras,
2000). Mastitis losses can be classified as direct or indi-
rect. Direct costs are due to treatment (drugs), discarded
milk (unmarketable milk due to antibiotic residues),
veterinary assistance, and extra labor. Indirect costs are
“hidden costs”: reduction of production (milk unprodu-
ced regarding to a healthy cow), involuntary culling, and
even, worsening of milk quality because of changes in
milk composition (Rajala-Schultz et al., 1999; Østeras,
2000). Costs reported in literature range from 43 to
189 (equivalent to 145 to 325 per cow and year)
depending on monetary unit and country (i.e. prices),
severity level, age of cow, and on concepts considered
on calculations.
Because of all mentioned above, mastitis is conside-
red in breeding programs since long time. It has low
heritability, from 0.01 to 0.11 (Rupp and Boichard,
1999; Carlén et al., 2004; Zwald et al., 2006). However,
mastitis is not routinely recorded at commercial farms,
and then, it has been mostly dealt indirectly by using
indicator traits such as udder conformation, somatic cell
count, and milking ease. Those traits are more heritable
than mastitis and show high genetic correlations with
the disease (Lund et al., 1994). Progressively, most
countries included some of them in their selection inde-
xes with the aim of selecting mastitis resistant animals
(Miglior et al., 2005; Shook, 2006).
The aim of this study was to deal with mastitis in
Spanish dairy cows using on farm records in order to
reconsider clinical mastitis in the breeding goal. Then,
specific objectives were to determine mastitis incidence
and factors of risk, to analyze whether yield production
has been affected, and to quantify mastitis costs, along
2006.
Material and methods
Since April 2005, clinical mastitis incidence are
being recorded at some Spanish herds from Basque
Autonomous Region (A.R.) and Gerona. Special sheets
have been designed jointly between farmers associa-
tions (EFRIFE and AFRIGI) and researchers from Ani-
mal Production Department of Polytechnic University
of Madrid (UPM). Farmers (or corresponding veteri-
nary) fill those sheets and associations send them perio-
dically to UPM, where herd, cow identification, quarter
affected, dates of beginning (diagnosis) and end of tre-
atment, treatment applied, and any observation are digi-
talized. Clinical mastitis was diagnosed when a cow had
visually abnormal milk secretion from one or more
quarters or by signs of inflammation of the udder tissue.
For a same cow, two cases were considered as indepen-
dent when dates of diagnosis did not match and did not
overlap treatment period, regardless how many quarters
were affected.
Data were edited according to different analysis in
order to use as much reliable information as possible.
Data from 25 herds (2,593 total cows) with continuous
mastitis recording were used. Clinical cases of cows
with complete and 305 days standardized lactation from
616 M. A. Pérez-Cabal et al. / Span J Agric Res (2008) 6(4), 615-622
Clinical mastitis in Spanish dairy cows 617
the beginning of data recollection to December 2006
were used to study mastitis dynamic throughout lacta-
tion (307 cases of 184 infected lactations). Mastitis inci-
dence and cost per case were determined using all the
infections available in 2006 (1,054 cases from 643
infected cows), while cost per cow, effects of factors on
udder health, and influence on total production were
studied from lactations with calving from October 2005
and completed along 2006, using both healthy and mas-
titic cows (587 lactations).
Mastitis incidence was calculated, per year and per
three-month periods, as follows:
Incidence (%)= Cows with one case at least
Total cows (healthy and mastitic)
Recurrence was the ratio from number of cases and
total infected cows.
Statistical analyses
Descriptive analyses were done to study mastitis dis-
tribution along the lactation. Management factors with
potential effects on the incidence of mastitis were analy-
zed using GLM procedure of statistical package SAS
(2001) for the sample under study. Fixed models were
analyzed including always herd (25 classes) plus the
following effects: calving month (7 classes: October to
December 2005 and from January to April 2006), sea-
son of year of calving (2 classes: 2005 and 2006), lacta-
tion number (3 classes: first, second, and third or more
lactation), 305 days milk production (as covariate).
Interactions between calving month (and season) and
parity were also studied. Mastitis occurrence within lac-
tation (yes/no) was considered as dependant variable.
Differences among least square means within effects
were analyzed using Tukey’s multiple means compari-
son test at 5% significance level. Odds ratios between
levels for significant effects using models from GLM
results were performed by LOGISTIC procedure.
Mastitis costs
Cost per case. Only costs due to treatment of each
case were calculated, including treatment administration
(TREAT) and discarded milk costs (DISC). Other costs
such veterinary honoraries and production loss, were
not included because of incomplete information (there
is a survey in process of veterinary costs) and the need
of more extensive timeframe to estimate loss in milk
production. Individual treatment cost was obtained as
follows:
TREAT = unit cost ×daily units ×treatdays
Where unit cost is the cost of each applied unit of
each product (milliliters or intramammary syringes);
daily units is the quantity needed per day; treatdays is
administration period (in days) for each medicine. Ave-
rage prices of different medicines and dosage recom-
mendations provided by veterinary services and enter-
prises were used to estimate product unit costs.
Along treatment period and withdrawal time (follo-
wing indications of pharmaceutical laboratories for
each product) milk was considered unmarketable to
avoid antibiotic residuals in milk for human consump-
tion. If more than one product was used as treatment,
the longer withdrawal time was used. Discarded milk
costs were individually estimated as follows:
DISC = daymilk ×pmilk ×(treatdays+withdrawal)
Where daymilk is daily milk production (in kg);
pmilk is average price of milk in 2006 (0.31 kg-1); tre-
atdays is administration period (in days) for each medi-
cine; withdrawal is days after the last administration.
Individual daily milk production at the onset of each
mastitis case was estimated using updated to January
2007 monthly milking records, provided by associa-
tions, following some rules:
– If onset occurred between calving and first
monthly control, average daily production was
assumed the same as the first control.
If onset occurred between two monthly controls,
two intervals were considered (before and after
midpoint). Daily production was estimated as the
production at corresponding midpoint interval.
If onset occurred after the last control record, one
of the following situations was considered:
If lactation was completed (dry date was
known). If onset was before dry day, daily pro-
duction was assumed the same as the last con-
trol (zero otherwise).
If lactation was uncompleted (unknown dry
day). If onset was previous to control nine (270
days in lactation), cow was considered still in
lactation and daily production was assumed the
same as the last control (zero otherwise).
If two following cases occurred, overlapped
milk discarded was taking into account to avoid
double counting.
Cost per cow. Only one lactation per cow was available
because of the short timeframe of this study. Then, cost
per cow can be considered as cost per lactation as well. It
was calculated as the sum of costs of all cases of the cow.
Results
Mastitis incidence and recurrence
Summary of data by parity and mastitis status
(healthy/mastitic), average 305 days milk, fat, and pro-
tein yields are shown in Table 1, as well as average days
in milk. Average cow from population produced 9,603
kg of milk in 328 days of lactation. Average production
of healthy cows was 8,931 kg and 9,838 kg of milk, 323
kg and 354 kg of fat, and 278 kg and 314 kg of protein,
for Gerona and Basque A.R., respectively. For mastitis
cows, 9,320 kg and 9,929 kg of milk, 328 kg and 357 kg
of fat, and 292 kg and 325 kg of protein, for Gerona and
Basque A.R., were found.
Average mastitis incidence in 2006 was 24.76%.
Incidence at average herds from Gerona was higher than
in Basque A.R. (31% and 19%, respectively). In the
period of study, 1,054 cases (477 in Basque A.R. and
577 in Gerona) corresponding to 643 cows were recor-
ded. Then, an average recurrence of 1.64 cases per cow
was obtained. A 38% of cows presented more than one
mastitis episode. Moreover, almost 13% of infected
cows had at least three cases in 2006. Figure 1 presents
mastitis incidence by lactation number and zone over all
population. In general, first lactation cows had lower
mastitis frequency (6%) than multiparous (8% and 10%
for second and third plus lactations, respectively). Incre-
asing trends by lactation number were more pronounced
in Basque A.R. Frequencies for primiparous in Gerona
were almost two-fold than in Basque A.R. (8% and 5%,
respectively).
Clinical mastitis distribution
Along 2006, the first three-month period (winter)
showed 32% of infections, followed by summer (26%),
spring, and autumn, with 22% and 20%, respectively.
Three-monthly distribution of clinical mastitis cases is
presented in Figure 2. By regions, in Gerona, winter and
summer were the most prevalent periods, whereas in
Basque A.R. was the first three months of 2006. Pro-
bably reasons are weather and labor time. Farmers justi-
fied that spring is the busiest period of the year and they
usually spent less time on recording data, as well as in
autumn. Then, maybe the information in late 2006 could
not be complete.
The 49% of all mastitis cases occurred within 90
days after calving (not shown). Distribution of first
618 M. A. Pérez-Cabal et al. / Span J Agric Res (2008) 6(4), 615-622
Complete lactations in 2006
Gerona Basque A.R.
Population
of 25 herds Healthy Mastitic Healthy Mastitic
Cows 2,593 161 104 242 80
- First lactation 1,436 77 35 122 16
- Second lactation 608 46 27 57 26
- Rest of lactations 549 38 42 63 38
305 days kg milk 9,603 ± 1,939 8,931 ± 1,781 9,320 ± 1,521 9,838 ± 2,190 9,929 ± 1,986
305 days kg fat 344 ± 74 323 ± 71 328 ± 66 354 ± 83 357 ± 75
305 days kg protein 302 ± 58 278 ± 55 292 ± 49 314 ± 56 325 ± 52
Days in lactation 328 ± 111 315 ± 41 313 ± 37 309 ± 43 315 ± 49
A.R.: autonomous region
Table 1. Data considered in this study: number of cows, production yield and lactation length
and lactation number were found. Nor were interactions
neither 305 days production as covariate. Regarding to
lactation number, multiparous cows were more liable to
suffer mastitis (coefficient of determination of 0.1438).
Odds ratios for first and second lactation regarding to
third and more lactations were 28% and 69%, respecti-
vely. There were not differences in milk, fat, and protein
yield per lactation between healthy and mastitic cows.
Stage of lactation did not result statistically significant
on mastitis incidence.
Mastitis costs
Average mastitis case cost was 73.93 (Table 2).
Discarded milk costs represented 74% of total cost per
case. Regarding to lactation number, average mastitis
case in primiparous was slightly cheaper than a case in
multiparous. Costs were higher for cows with at least
three calvings than for cows in second lactation in Gero-
na whereas in Basque A.R. costs were similar. Taking
Clinical mastitis in Spanish dairy cows 619
infections throughout lactation is presented in Figure 3,
for first, second and third or more lactations. First case
was mostly diagnosed in the first month (29%). After
this period, behavior of primiparous and multiparous
was slightly different. Cows with more than one calving
showed first infection mostly at early lactation whereas
in primiparous 12% of first cases also occurred over
270 days in milk. In Figure 4, weekly distribution over
the first four months of lactation is shown. Cows in first
lactation were most prone to mastitis within the first 7
days after calving, whereas for multiparous liability
remained until fourth week.
Management factors and mastitis effect
on production
Calving month (and season), production level, and
age of cow (by parity) were analyzed as factors of risk
using completed lactations in 2006. No statistically sig-
nificant effects (at 5% level) on mastitis other than herd
Figure 1. Mastitis incidence (%) in first (LACT1), second
(LACT2), and rest of lactations (LACT3+) for Gerona,
Basque Autonomous Region, and average population.
Figure 3. First-case mastitis occurrence throughout lactation
by parity.
Figure 4. Distribution of first mastitis cases within the first
four months of lactation by parity.
Figure 2. Distribution of clinical mastitis cases by three-
month periods of 2006.
12
10
8
6
4
2
0
%
Gerona Basque A.R. Average 0-30
%
35
30
25
20
15
10
Weeks in milk
Year 2006
1 2 3 4 5 6 7 8 9 10111213141516
30
%
% cases
40
35
30
25
20
15
10
5
0
Winter
Gerona Basque A.R. Average
Spring Summer Autumn
25
20
15
10
5
0
5
031-60 61-90 91-120 121-150 151-180
Days in milk 181-210 211-240 241-270 271-300 >300
620 M. A. Pérez-Cabal et al. / Span J Agric Res (2008) 6(4), 615-622
into account all cases throughout a lactation, mastitis
cost per infected cow and lactation was 117 , what
represents 29 per present cow at herd.
Discussion
Average mastitis incidence in our population agreed
with other studies. Literature reports mastitis incidences
from 11% to 40% in different dairy populations
(Heringstad et al., 2000; Kadarmideen and Pryce, 2001;
Va l de et al., 2005). Results obtained by lactation num-
ber are in accordance too with those populations, with
statistically significant higher frequency in multiparous
than in first-lactation cows (Hagnestam et al., 2007).
Cows with more than one calving were more prone to
mastitis due to physical alterations of udder. Along the
productive life, teat canal loses its elasticity and udder
attachments become relaxed, increasing the risk of mas-
titis (Zwald et al., 2004b). Regarding to recurrence, our
results (1.64) were slightly higher than, for instance, 1.4
reported by Wilson et al. (2004), and should be remar-
ked that 38% of cows were recurrent.
Descriptive analyses regarding to mastitis distribu-
tion throughout lactation and risky seasons were consis-
tent with larger populations. However, the small data set
could have conditioned statistical analyses and unexpec-
ted results were found. For instance, the effect of pro-
duction level could have been hidden by herd, which
absorbed almost all variability. Further, consequences
of mastitis on lactation yielding could also be biased
due to conditions imposed such as using 305 days stan-
dardized lactations, because there was no difference bet-
ween a cow culled by mastitis before a minimum mil-
king period and another with lactation in course. Howe-
ver, despite no significant differences were found by
stage of lactation our results were similar to other stu-
dies. The most liable period was the first month of lac-
tation, as also found Carlén et al. (2004), Zwald et al.
(2004a, 2006), and Harder et al. (2006). First cases of
primiparous occurred mostly during the first week
(Rajala-Schultz et al., 1999; Wilson et al., 2004). Some
differences in mastitis distribution were found in first
and second-plus lactations with other works. Wilson et
al. (2004) reported that in primiparous fewer cases were
detected from the second week onward while in our
study mastitis increased in last stages, close to next cal-
ving. Regarding to calving season (or calving month),
there is no consensus in literature. Rupp (1999) found
statistically significant more incidences in heifers (but
not in multiparous) with calvings from November to
April. Other studies showed summer as the most
influencing period because of heat stress. Riekerink et
al. (2007) pointed out that influence of calving season is
different depending on pathogens involved.
Average costs in Gerona and Basque A.R. were 80.50
and 66.28 per case, respectively. Differences were
due to treatment protocols applied in both zones. Eco-
nomic losses due to mastitis were estimated at 117
per infected cow and lactation (29 per cow present in
herd). Literature reports a wide range of mastitis costs
depending on concepts included on calculations. Wolfo-
et al. (2006) estimated losses from 43.63 to 84.84
in Czech Republic, including costs from discarded
milk, drugs, veterinary service, extra labor time, anti-
biotic for drying of cows, and an extra milking machi-
ne. For a population from United States, Shim et al.
(2004) reported 134 as losses from milk (unproduced
and unmarketable) and treatment. Mastitis was more
expensive in multiparous than first-lactation cows
because of higher milk yield. Taking into account the
results obtained, in an average herd of our population
with 110 cows, mastitis costs were 3,190 per year,
only counting for treatment and discarded milk, and it
would be higher if milk price increases.
Then, this study dealing with clinical mastitis in Spain
from on farm data reported a way to estimate mastitis
costs due to treatment and discarded milk. Future works
should consider veterinary, milk yield reduction, and
replacement costs in order to take into account mastitis in
a profit function to obtain economic importance of masti-
tis regarding to other production traits. Moreover, with the
final aim of including resistance to clinical mastitis in the
Gerona Basque A.R. Average
Cost/case 80.50 ± 31.94 66.28 ± 30.96 73.93 ± 32.26
Treatment 23.32 ± 16.95 19.55 ± 14.79 21.57 ± 16.07
Discarded milk 59.24 ± 20.85 49.06 ± 24.65 54.57 ± 23.22
LACT1 72.50 ± 27.38 56.75 ± 25.64 66.64 ± 27.74
LACT2 82.19 ± 32.30 68.61 ± 28.80 76.05 ± 31.46
LACT3+ 85.54 ± 33.96 68.79 ± 33.90 76.67 ± 34.90
Cost/cow 116.09 ± 58.63 117.74 ± 77.44 116.85 ± 67.71
LACT1 100.49 ± 53.93 104.21 ± 81.34 101.81 ± 63.66
LACT2 135.33 ± 72.73 99.21 ± 57.96 117.73 ± 67.61
LACT3+ 113.75 ± 49.13 133.89 ± 84.96 123.82 ± 69.57
Table 2. Average mastitis costs () and case costs () for first
(LACT1), second (LACT2), and later lactations (LACT3+) by
regions
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Clinical mastitis in Spanish dairy cows 621
breeding goal on selection scheme by developing an udder
health index, as much information as possible it is neces-
sary to obtain reliable genetic evaluations and parameters
of clinical mastitis because of the low heritability showed
in other studies. Thus, because of the concern of dairy far-
mers in animals without health problems to avoid extra-
costs, it would be recommended to implement a routinely
recording system of clinical mastitis throughout the Spa-
nish dairy population.
Acknowledgements
Authors are grateful to farmers for their inestimable
effort and want to acknowledge the Holstein Associa-
tions EFRIFE and AFRIGI their cooperation. This work
has been supported by MITC (PDT2004-0168).
References
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Genetic selection has increased production levels of livestock species considerably. However, apart from a favourable increase in production, animals in a population that have been selected for high production efficiency seem to be more at risk for behavioural, physiological and immunological problems. Examples are presented of over 100 references on undesirable (cor)related effects of selection for high production efficiency, with respect to metabolic, reproduction and health traits, in broilers, pigs and dairy cattle. A biological explanation for the occurrence of negative side effects of selection is presented. Genetic selection may lead to loss of the homeostatic balance of animals, resulting in the occurrence of pathologies and consequently in impaired animal welfare. Future application of modern reproduction and DNA-techniques in animal breeding may increase production levels even faster than at present, which may result in more dramatic consequences for behavioural, physiological and immunological traits. Selection for more than production traits alone may prevent such. Without knowledge about the underlying physiological processes on which genetic selection acts, selection is essentially a black box technique. Knowledge of biological backgrounds will offer the opportunity to understand, anticipate and prevent undesirable side effects of selection.
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The objective of this work was to establish economic values (EVs) of mastitis and lameness in order to enhance the current UK dairy profit index (£PLI) by including these health traits. The EVs of traits currently in £PLI were also re-evaluated to account for changes in costs/returns over time and to determine their sensitivity to changes in some of the basic assumptions used in their derivation. Predicted transmitting abilities (PTAs) for mastitis are not available in the UK. Instead, PTAs for somatic cell count (SCC), which has a strong genetic correlation with clinical mastitis, were used to predict clinical mastitis. Similarly, PTAs for locomotion and (for bulls with no locomotion PTA) the ‘legs and feet’ composite were used to predict lameness. The EV of mastitis was estimated at £0·83 per percent incidence, giving an index weight for SCC PTA of £0·20. The EV of lameness was estimated at £0·99 per percent incidence, giving an index weight for locomotion PTA of £1·28. The associated index weight for the ‘legs and feet’ composite was estimated to be £1·50. Economic values for all traits (production, lifespan, mastitis and lameness) were found to be sensitive to their associated price assumption but not to price assumptions of other traits in the index or to other production parameters in the model. Better information is needed on the influence of cow age (parity) on incidence of disease and on the probability of involuntary culling to determine the appropriate balance between the EVs for longevity and health. Currently, 16% of the weight in £PLI is attributable to non-production traits. In our revised index this weight increased to 23%. Even so, selection using this index is still predicted to result in an increase in mastitis and lameness, albeit at a very low rate. This situation may be changed by the introduction of fertility into £PLI and through better information about health traits. Incorporation of consumer preference into £PLI may require traits associated with health and welfare of the cow to receive more weight than their EV would suggest in order to maintain or improve health traits in national selection programmes.
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Heritabilities and genetic and phenotypic correlations were estimated for linear scored udder traits, clinical mastitis, incidence of other diseases, and somatic cell count (SCC), using first lactation data from the Danish young sire sampling program. Two sets of data were analyzed using a multi-trait REML procedure with an animal model. Heritabilities were low for mastitis (0.025) and other diseases (0.011). Heritability of SCC was 0.18. For type traits, heritability estimates varied between 0.07 and 0.43. The estimate of the genetic correlation between SCC and clinical mastitis was high at 0.97. Genetic correlations between health and type traits were generally low ( - 0.32 to 0.37) with few exceptions. The genetic correlation between clinical mastitis and other diseases was moderately high at 0.53. All phenotypic correlations between traits were low. In general, the results indicate that selection for improved udder conformation will reduce the increase in SCC and clinical mastitis associated with selection for production. The high genetic correlation between SCC and clinical mastitis makes SCC a feasible indicator for clinical mastitis.
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The literature concerning selection for mastitis resistance in dairy cattle is reviewed and the reasons for including mastitis resistance in dairy cattle breeding programs are described. The current situation in Denmark, Finland, Norway and Sweden is described with emphasis on the data recording schemes and the choice of models used for breeding value estimation. The use of clinical mastitis data and somatic cell counts in selection for mastitis resistance as well as implications and prospects for the future are discussed.
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Reproduction and health traits are of significant economic importance for dairy production. Most of these traits are expressed in a categorical way and show heritabilities of 5% or less. Nevertheless, their additive genetic variation is considerable. For example, the incidence of clinical mastitis in the first lactation varies among daughter groups of Swedish Holstein bulls between 10 and 26%, stillbirth rate at first parity between 3 and 16%, and the number of inseminations per serviced cow between 1.6 and 1.9. Unfavourable genetic correlations of the order of 0.2–0.4 between production on one side, and mastitis and female fertility on the other, have generally been found. Well integrated recording schemes in the Scandinavian countries enabled early the adoption of total merit indexes (TMI), including reproduction and health traits, into their selection schemes. In practice, TMI selection has proven to be effective in maintaining functional efficiency of the cows simultaneously with a sharp increase in production. As bull selection nowadays takes place globally, sustainable breeding programmes require more extensive recording and genetic evaluations of reproduction and health traits internationally, a development that presently grows quickly. The Scandinavian experiences are reviewed in this paper in the light of this international development.
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The effect of clinical mastitis on milk yield was studied in 24,276 Finnish Ayrshire cows that calved in 1993 and were followed for one lactation (i.e., until culling or the next calving). Cows that had only mastitis, but no other diseases, and cows that had no diseases (healthy cows) during the lactation were included in the study. Monthly test day milk yields were treated as repeated measurements within an animal in a mixed model analysis. Mastitis index categories were created to relate the timing of mastitis to the test day milk measures. Statistical models (a separate model for each parity) included fixed effects of calving season, stage of lactation, and mastitis index. An autoregressive correlation structure was used to model the association among the repeated measurements. The effect of mastitis occurring at different periods during the lactation was studied. The daily loss during the first 2 wk after the occurrence of mastitis varied from 1.0 to 2.5 kg, and the total loss over the entire lactation varied from 110 to 552 kg and depended on parity and the time of mastitis occurrence. Regardless of the time of occurrence during the lactation, mastitis had a long-lasting effect on milk yield; cows with mastitis did not reach their premastitis milk yields during the remainder of the lactation after onset of the disease.