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1999 J Dairy Sci 82:205–214 205
Received May 11, 1998.
Accepted September 9, 1998.
Genetic Parameters for the Milk Coagulation
Properties and Prevalence of Noncoagulating Milk
in Finnish Dairy Cows
T. IKONEN, K. AHLFORS, R. KEMPE,
M. OJALA, and O. RUOTTINEN
Department of Animal Science, University of Helsinki,
PO Box 28, 00014 Helsinki University, Finland
ABSTRACT
The genetic parameters were estimated for milk
coagulation properties and milk production traits,
and the prevalence of noncoagulating milk in the
Finnish dairy cattle population was investigated.
Data were included for 789 Finnish Ayrshire cows
and 86 Finnish Friesian cows from 51 herds. The
animal model used for estimation included fixed ef-
fects for parity, stage of lactation, breed, and herd.
Further, effects of milk protein genotypes on pheno-
typic and genetic variation in the studied traits were
examined. Heritability estimates for the milk coagu-
lation properties were moderately high. The k-casein
B allele was associated with the best phenotypic and
genetic values for curd firmness, and the A and E
alleles were associated with the poorest. About 24% of
the additive genetic variation in the curd firmness
was due to milk protein polymorphism. About 8% of
the Finnish Ayrshire cows in the present study
produced noncoagulating milk. Because of the occur-
rence of the noncoagulating milk and a possibly un-
favorable genetic trend in the milk coagulation
properties, it would be important to improve these
traits in the Finnish Ayrshire breed. Milk coagulation
properties could be improved directly by selecting for
these traits or indirectly by favoring the k-casein B
allele or by selecting against genetic markers as-
sociated with poorly coagulating or noncoagulating
milk.
(Key words: milk coagulation, noncoagulation,
genetic parameters, Finnish dairy cows)
Abbreviation key:FAy = Finnish Ayrshire, FFr =
Finnish Friesian, NC = noncoagulating.
INTRODUCTION
The importance of cheese production has increased
during the past 15 yr in Finland, and currently about
40% of the milk produced there is used for cheese
production. The coagulation ability of milk is essen-
tial in cheese making. Milk with favorable coagula-
tion properties (i.e., short coagulation and curd-
firming times and a firm curd) is expected to give
more cheese with desirable composition than milk
with unfavorable properties (3, 6).
There are no published data on variation or trend
in the milk coagulation properties over the past de-
cades in Finland. However, according to the observa-
tions made in Finnish dairies, the average coagula-
tion ability of milk has been deteriorating during the
past 20 to 30 yr. Consequently, to be able to produce
the same amount of cheese, more milk is needed
today than in recent decades. In addition, two Finnish
data sets collected in 1980s (29) and 1990s (12)
showed that 3.6% of 168 Finnish Ayrshire ( FAy)
cows and 10.2% of 59 FAy cows, respectively,
produced noncoagulating ( NC) milk.
Because of the importance of cheese production in
Finland, there is an interest in halting the undesira-
ble trend in milk coagulation properties and in im-
proving these traits. Consequently, reasons for the
unfavorable changes and variation in the coagulation
properties have to be identified. Should a reasonable
part of the variation in the milk coagulation proper-
ties be genetic, these characteristics could be im-
proved by selection. In addition, it is important to find
out whether the relatively high frequency of NC milk
that has been reported in (12, 29) was by chance or is
a common phenomenon in the Finnish dairy cattle
population.
Heritability estimates for the milk coagulation
properties have been estimated in only a few studies
(15, 25, 29), none of which used an animal model to
account for all known genetic relationships among
animals. Because of the small data sets and statisti-
cal procedures assumed, some heritability estimates
were not reliable. The results of the previous studies
implied, however, that a moderate part of the varia-
tion in the milk coagulation properties could be due to
additive genetic effects.
Journal of Dairy Science Vol. 82, No. 1, 1999
IKONEN ET AL.
206
The lack of suitable equipment for routine determi-
nation of the milk coagulation properties in the na-
tional cow population would restrict possibilities of
direct selection for these traits. An indirect way of
improving the milk coagulation properties might pos-
sibly be to favor the k-CN B allele or alleles at other
loci that are associated with favorable coagulation
properties. The k-CN B allele is known to be as-
sociated with more desirable coagulation properties
(1, 4, 12, 19, 26, 28, 29, 30) and protein composition
of milk (12, 19, 22, 28) than is the A allele, but no
reliable estimates exist of the effect of the k-CN E
allele on these traits. The k-CN E allele is rather
common (30%) in the FAy (13), the main dairy
breed in Finland.
Another indirect way of improving the milk coagu-
lation properties might be to breed for routinely
recorded dairy traits that correlate favorably with the
milk coagulation properties. Genetic correlations be-
tween the milk coagulation properties and milk
production traits have thus far been estimated from
only a few, small data sets (15, 25). Reliable esti-
mates for the genetic correlations between the milk
coagulation properties and milk production traits are
therefore needed.
The objectives of this study were to estimate
genetic parameters (heritabilities and genetic corre-
lations) for milk coagulation properties and milk
production traits and to estimate the prevalence of
NC milk in the Finnish dairy cattle population.
MATERIALS AND METHODS
Data
A total of 789 FAy and 86 Finnish Friesian (FFr)
cows from 51 herds in southern Finland were sampled
once during the period from February to April 1995.
The milk samples were a mixture of evening and
morning milkings; samples were analyzed for milk
coagulation properties, pH, milk yield, fat percentage,
protein percentage, SCC, and major milk protein
genotypes.
Background information about the cows and herds
was obtained from national milk recording data sets
from Agricultural Data Processing Centre (Vantaa,
Finland). It was not possible to get detailed informa-
tion about the feeding of the cows, although feeding
procedures can affect milk coagulation properties (1,
8, 19).
Laboratory Analyses
The milk coagulation properties were determined
at 32°C using a Formagraph (Foss Electric A/S,
Hillerød, Denmark) in the laboratory of the Food
Research Institute of Agricultural Research Centre
(Jokioinen, Finland). Rennet (Renco Calf Rennet Li-
quid; New Zealand Rennet Company Ltd., Eltham,
New Zealand) was diluted in 0.07 Msodium acetate
buffer (1:100, vol/vol; pH 5.5). The pH of milk was
determined (PHM82 Standard pH Meter; Radiome-
ter, Copenhagen, Denmark).
The milk samples were allowed to coagulate for 30
min because, during the cheese-making process, curd
is usually cut 30 min after the addition of rennet to
the milk. The three milk coagulation properties deter-
mined were milk coagulation time in minutes, curd-
firming time in minutes, and firmness of the curd in
millimeters. Milk coagulation time was the time from
the addition of rennet to milk to the beginning of
coagulation. Curd-firming time was the time from the
beginning of coagulation to the moment the width of
the curve was 20 mm. Firmness of the curd was the
width of the curve 30 min after the addition of rennet.
The milk samples that did not form curd in 30 min
(i.e., a straight line on the output paper) were de-
fined as NC samples.
Fat and protein percentages were determined us-
ing a Milko Scan 605 (Foss Electric A/S), and SCC
was determined by means of a Fossomatic 360 (Foss
Electric A/S) in local dairy laboratories. The fre-
quency distribution for SCC was not normal, so SCC
were logarithmically transformed. Genotypes for the
as1-CN, b-CN, k-CN, and b-LG were determined in
Finnish Animal Breeding Association laboratory
(Vantaa, Finland) using isoelectric focusing as
described by Erhardt (5).
Statistical Analyses
Univariate and bivariate models. Heritabilities
for the studied traits and genetic correlations between
the milk coagulation properties and milk production
traits were first estimated using an univariate and a
bivariate model:
yijklmn =m+ parityi+ stagej+ breedk+ herdl+
animm+eijklmn,[1]
where
yijklmn = milk coagulation or milk production trait,
m= mean,
parityi= fixed effect of parity i (i = 1 to 4),
stagej= fixed effect for stage of lactation j (j = 1 to
6),
breedk= fixed effect of breed k (k = 1 to 2),
Journal of Dairy Science Vol. 82, No. 1, 1999
GENETIC PARAMETERS FOR MILK COAGULATION 207
herdl= fixed effect of herd l (l = 1 to 51),
animm= random additive genetic effect of animal
m, N(0, ), andAsa
2
eijklmn =random residual effect, N(0,).Ise
2
A variance-covariance structure between studied
traits 1 and 2 for a bivariate model was assumed,
where sa1a2 and se1e2are additive genetic and
residual covariances between traits 1 and 2:
Var =
a1
a2
e1
e2
Asa1
2
Asa1a2
0
0
Asa1a2
Asa2
2
0
0
0
0
Ise1
2
Ise1e2
0
0
Ise1e2
Ise2
2
Parity was grouped in four classes: first, second,
third, and fourth to ninth parities; stage of lactation
was grouped into six classes: 5 to 30 d, 31 to 60 d, 61
to 120 d, 121 to 180 d, 181 to 240 d, and >240 d after
calving; and breed was grouped into two classes: FAy
and FFr. Herd was treated as a fixed effect because
the herds were a group selected from a certain area,
and differences in the milk coagulation properties
between them were of interest. Of the 51 herds, 33
were pure FAy herds, 1 was a pure FFr herd, and 17
were mixed herds. The number of animals per herd
ranged from 6 to 47.
The 789 FAy and 86 FFr cows with records were
daughters of 246 FAy and 41 FFr sires, respectively.
The average number of daughters per sire was only 3
but ranged from 1 to 79. The pedigree information
consisted of parents and grandparents of the cows
with records, and the total number of animals in the
statistical analyses was 2757.
Variance and covariance components for the ran-
dom effects were estimated from the data using the
REML VCE package (10). Solutions for the fixed and
random effects in the models were obtained using the
PEST package (9), and statistical significance of the
fixed effects was tested using the Ftest provided by
the PEST package (9).
Multivariate models. In addition to univariate
and bivariate analyses, heritabilities for the studied
traits and genetic correlations between the milk
coagulation properties and milk production traits
were estimated using a corresponding multivariate
model, in which a milk coagulation characteristic was
analyzed simultaneously with pH, milk yield, fat per-
centage, protein percentage, and SCC. The multivari-
ate model was used to determine whether more relia-
ble and more accurate estimates for the genetic
parameters would be obtained when information on
phenotypic and genetic association between all
studied traits was available.
Modification of the univariate model. In order
to estimate the effects of b-CN, k-CN, and b-LG geno-
types on the milk coagulation properties and to study
how their inclusion in the model affects additive
genetic variation in the coagulation properties, the
following model was assumed:
yijklmnop =m+ parityi+ stagej+ breedk+ herdl+
b-k-CNm+b-LGn+ animo+eijklmnop[2]
where
b-k-CNm= fixed effect of b-k-CN genotype class m
(m = 1 to 9), and
b-LGn= fixed effect of b-LG genotype
(n = 1 to 3).
The b-CN and k-CN were included in Model [2] as
composite b-k-CN grouped into nine genotype classes
(Figure 1). Because the k-CN B allele was rare
(0.08), the AB, BB, and BE genotypes of k-CN were
combined within each b-CN genotype. Being almost
monomorphic, as1-CN was not considered in the for-
mation of the composite casein genotypes. The b-LG
polymorphism was grouped into three genotype
classes: AA (n = 88), AB (n = 366), and BB (n =
421). Other effects, assumptions, and statistical
procedures used with Model [2] were identical to
those used with Model [1].
RESULTS AND DISCUSSION
Means and Variation
The milk coagulation properties varied considera-
bly (Table 1). About 8% of the milk samples did not
coagulate in 30 min (curd firmness = 0.0 mm), and,
thus, the distribution for the curd firmness was
skewed toward the lowest (i.e., the most undesirable)
values. In addition, every third milk sample did not
reach a curd firmness of 20 mm in 30 min. The
number of samples for the coagulation time and, espe-
cially, for the curd-firming time was, therefore, lower
than for curd firmness. The curd-firming time was
thus excluded from further statistical analyses.
Means and variation for the milk coagulation and
milk production traits (Table 1) were of the same
magnitude as those reported by Ikonen et al. (12).
Factors Affecting the Milk
Coagulation Properties
Parity. Milk yield, SCC, and pH increased with
parity (Table 2). Both SCC and pH usually have an
Journal of Dairy Science Vol. 82, No. 1, 1999
IKONEN ET AL.
208
Figure 1. Estimates of effect of the b-k-CN genotypes on the milk coagulation properties. 1AB (n = 5) + BB (n = 1) + BE (n = 26); 2AB
(n=80)+BB(n =2) +BE(n=6);3AB (n = 13) + BB (n = 1).
TABLE 1. Means and variation in the milk coagulation and milk production traits.
1Number of cows and observations.
2Coefficient of variation, expressed as a percentage.
3Milk samples that coagulated in 30 min.
n1X Minimum Maximum CV2
Coagulation time,3min 809 12.3 3.5 30.0 41
Curd-firming time, min 587 9.6 1.5 23.0 47
Curd firmness, mm 875 23.2 0.0 56.0 57
Curd firmness,3mm 809 25.1 1.0 56.0 50
pH 875 6.78 6.58 7.12 1
Daily milk yield, kg 875 24.8 6.0 53.2 31
Fat content, % 875 4.41 2.29 7.80 16
Protein content, % 875 3.35 2.45 4.81 11
Log-transformed SCC 875 4.28 1.39 8.58 29
unfavorable effect on the milk coagulation properties
[e.g., (26, 27)]. Parity had, however, no statistically
significant ( P= 0.423) effect on the milk coagulation
properties. Similar results were observed also in some
other studies (4, 15, 26), but, in the study of Schaar
et al. (28), the milk coagulation properties improved
with parity.
Stage of lactation. The milk coagulation proper-
ties were at their best during the 1st mo of lactation
(5 to 30 d after calving) and again from the 9th mo
(>240 d after calving) onward (Table 3). The
changes in the curd firmness over the course of lacta-
tion were parallel to those in protein and fat percent-
ages and in SCC and were almost opposite to the
changes in milk yield over lactation (Table 3). This
result agrees with those reported in (12, 14), but, in
others (4, 24), the milk coagulation properties deteri-
orated as lactation proceeded. In (15, 26, 28), stage of
lactation had no effect on the milk coagulation proper-
ties. Confounded effects for stage of lactation and
season in some of the previous studies may partially
explain the contradictory results for the effect of stage
of lactation on the milk coagulation properties.
Breed. The milk coagulation properties were on
average better for the FFr than for the FAy cows
(Table 4), which was in part because NC milk was
found only in the FAy. Also a difference between the
breeds in pH of milk explained some of the differences
Journal of Dairy Science Vol. 82, No. 1, 1999
GENETIC PARAMETERS FOR MILK COAGULATION 209
TABLE 2. Estimates (Est.) of effect of parity relative to the first parity class on the milk coagulation
and milk production traits.
1Milk samples that coagulated in 30 min.
Parity
12 3 4to9
(n = 313) (n = 240) (n = 148) (n = 174) P
Est. SE Est. SE Est. SE
Coagulation time,1min 0 0.2 0.5 –0.4 0.5 –0.6 0.5 0.423
Curd firmness, mm 0 –0.1 1.1 2.1 1.2 2.5 1.2 0.066
pH 0 0.03 0.01 0.05 0.01 0.04 0.01 <0.001
Daily milk yield, kg 0 2.4 0.5 3.3 0.5 5.1 0.5 <0.001
Fat content, % 0 0.00 0.05 –0.04 0.06 –0.10 0.06 0.342
Protein content, % 0 0.09 0.02 –0.02 0.03 –0.03 0.03 <0.001
Log-transformed SCC 0 0.44 0.10 0.46 0.12 0.58 0.11 <0.001
TABLE 3. Estimates (Est.) of effect for stage of lactation relative to the fourth stage of lactation class on the milk coagulation and milk
production traits.
1Milk samples that coagulated in 30 min.
Days after calving
5 to 30 31 to 60 61 to 120 121 to 180 181 to 240 >240
(n = 56) (n = 84) (n = 192) (n = 195) (n = 191) (n = 157) P
Est. SE Est. SE Est. SE Est. SE Est. SE
Coagulation time,1min –4.7 0.8 –1.8 0.7 –0.9 0.5 0 –1.5 0.5 –2.7 0.6 <0.001
Curd firmness, mm 9.8 1.8 0.9 1.6 0.4 1.2 0 4.6 1.2 11.4 1.3 <0.001
pH –0.06 0.01 –0.02 0.01 –0.02 0.01 0 –0.01 0.01 –0.01 0.01 <0.001
Daily milk yield, kg 3.9 0.8 5.9 0.7 4.6 0.5 0 –3.5 0.5 –7.9 0.6 <0.001
Fat content, % 0.38 0.09 –0.08 0.08 –0.19 0.06 0 0.15 0.06 0.54 0.07 <0.001
Protein content, % 0.01 0.04 –0.29 0.04 –0.21 0.03 0 0.16 0.03 0.37 0.03 <0.001
Log-transformed SCC20.29 0.17 –0.50 0.15 –0.22 0.12 0 0.23 0.12 0.64 0.13 <0.001
in the coagulation properties between the breeds. The
fat content of milk was higher for the FAy, whereas
there was no difference in protein content of milk
between the breeds.
The k-CN B allele, which had a favorable effect on
the milk coagulation properties (Figure 1), was more
frequent (chi-square test, P< 0.001) in FFr (0.14)
than in FAy (0.07). Casein polymorphism explained
only a negligible part of the differences in the milk
coagulation properties between the breeds because
the differences remained statistically significant after
the records were adjusted for the milk protein geno-
type effects (Table 4). In the study of Macheboeuf et
al. (19), the more favorable milk coagulation proper-
ties of Montbe
´liarde and Tarentaise cows compared
with those of Holstein cows were mostly due to differ-
ences between the breeds in the distribution of the k-
CN alleles and in the casein content of milk.
Herd. There was variation in the milk coagulation
time ( P< 0.050), milk yield, pH, fat percentage, and
protein percentage ( P< 0.001 for each previous trait)
and in the frequency of the k-CN B allele between the
herds (data not shown). As with the breed effect,
differences in the previous traits between the herds
were not due to k-CN polymorphism because the herd
effect on these traits was statistically significant after
the records were adjusted for the effects of milk pro-
tein genotypes. Erhardt et al. (6) found no difference
in the protein percentage of milk between the herds
with a high frequency (25.8%) of the k-CN B allele
and those herds with a low frequency (9.7%), but fat
percentage was higher in the herds with a high fre-
quency.
The β-κ-CN genotypes. Within each b-CN geno-
type, the k-CN B allele was associated with the most
favorable coagulation properties (Figure 1), as has
been observed in numerous studies (1, 4, 12, 26, 28,
29, 30). The k-CN E allele did not appear in combina-
tion with the b-CN A2A2genotype, but, within the
other two b-CN genotypes, the k-CN E allele was
Journal of Dairy Science Vol. 82, No. 1, 1999
IKONEN ET AL.
210
TABLE 4. Estimates (Est.) of differences between the Finnish Ayrshire (FAy) (n = 789) and the
Finnish Friesian (FFr) (n = 86) cows in milk coagulation and milk production traits.
1No milk protein genotypes in the model.
2b-k-CN and b-LG genotypes in the model.
3Milk samples that coagulated in 30 min.
Model [1]1Model [2]2
FAy–FFr PFAy–FFr P
Est. SE Est. SE
Coagulation time,3min 3.2 0.9 <0.001 2.0 0.9 0.024
Curd firmness, mm –9.8 2.3 <0.001 –7.8 2.3 0.001
pH 0.02 0.01 0.041 0.01 0.01 0.198
Daily milk yield, kg –2.5 0.9 0.007 –2.3 0.9 0.015
Fat content, % 0.36 0.12 0.003 0.29 0.13 0.025
Protein content, % 0.01 0.05 0.859 0.02 0.06 0.750
Log-transformed SCC4–0.17 0.20 0.378 –0.19 0.21 0.361
associated with the poorest milk coagulation proper-
ties. In addition, the frequency of the k-casein E allele
was somewhat higher among the cows with a non-
coagulating milk sample (0.36) than among other
cows (0.29), but the difference between the groups
was not significant. The unfavorable effect of the k-
CN E allele compared with that of the B and A alleles
was in agreement with the preliminary results ob-
tained for the FAy and FFr cows (12) andwith those
reported by Lodes et al. (16) and by Oloffs et al.
(25).
Milk production, pH, fat percentage, protein per-
centage, or SCC were not affected by the b-k-CN
genotypes, which agreed with the results reported by
Ikonen et al. (12). The favorable effect of the k-CN B
allele on protein percentage has been observed in
some studies (2, 11, 20) but not in others (7, 18, 23).
In addition to the favorable effect on milk coagulation
properties, the k-CN B allele was associated with a
high casein content (12, 28), with a high k-CN con-
tent (1, 12), and with small casein micelle size (17).
Hence, the total protein content of milk may not give
an accurate enough estimate of casein content or of
casein composition of milk. It is, however, the casein
that coagulates in the cheese-making process and
together with fat forms the major part of the dry
matter in cheese.
The β-LG genotypes. The milk coagulation time
was shortest for the b-LG AA genotype ( P< 0.001);
the curd firmness was not affected by the b-LG geno-
types (data not shown). The b-LG AA genotype had a
favorable effect on some or all milk coagulation
properties in some studies (19, 21, 30), but, in the
study of Pagnacco and Caroli (26), thegenotypes had
no effect on these properties.
Genetic Parameters
for the Milk Coagulation
Properties
There was a negligible or no difference between the
estimates of heritabilities and genetic correlations ob-
tained using a univariate or bivariate model and a
multivariate model. Standard errors of the estimates
were somewhat lower with a multivariate model than
with other models. Thus, estimates of heritabilities of
the traits and genetic correlations between a milk
coagulation trait and a milk production trait that
were obtained using a multivariate model are
presented (Table 5). The genetic correlation between
the coagulation time and the curd firmness was esti-
mated using a bivariate model because it was not
considered necessary to include these highly cor-
related traits in a multivariate analysis.
Heritability estimates. Heritability estimates for
the milk coagulation properties were moderately high
and were of the same magnitude as those estimated
for the milk production traits (Table 5). The herita-
bility estimate for the coagulation time obtained in
this study was somewhat lower than those reported in
other studies (15, 25), and the estimate for the curd
firmness was of the same magnitude as those
reported by Oloffs et al. (25) but was somewhat
higher than that reported by Tervala et al. (29).
When the records were adjusted for the b-k-CN and
b-LG genotype effects, estimates of additive genetic
variance for the coagulation time and the curd firm-
ness decreased by 20 and 24%, respectively. Thus,
additive genetic variation in these milk coagulation
properties was partially due to milk protein polymor-
phism. This result was parallel to the distinct effect of
the b-k-CN genotypes on the milk coagulation time
Journal of Dairy Science Vol. 82, No. 1, 1999
GENETIC PARAMETERS FOR MILK COAGULATION 211
TABLE 5. Heritability estimates (Est.) for the milk coagulation and milk production traits (on diagonal) and genetic correlations between
the traits (upper triangle).
1Milk samples that coagulated in 30 min.
1234567
Est. SE Est. SE Est. SE Est. SE Est. SE Est. SE Est. SE
1. Coagulation time,1min 0.22 0.05 –0.96 0.02 0.40 0.12 0.02 0.15 –0.01 0.10 0.49 0.08 –0.06 0.16
2. Curd firmness, mm 0.40 0.04 –0.30 0.07 –0.06 0.12 0.09 0.08 –0.24 0.07 0.18 0.13
3. pH 0.34 0.05 0.08 0.13 –0.12 0.08 –0.13 0.07 0.78 0.10
4. Daily milk yield, kg 0.16 0.05 –0.66 0.07 –0.56 0.09 0.08 0.16
5. Fat content, % 0.43 0.04 0.78 0.05 –0.31 0.16
6. Protein content, % 0.48 0.04 –0.22 0.17
7. Log-transformed SCC 0.09 0.03
and the curd firmness and to that of the b-LG geno-
types on the coagulation time. Estimates of additive
genetic variation in the other traits changed little, if
any, when the records were adjusted for the milk
protein genotype effects, which agreed with the
negligible effect of the genotypes on them. In the
study by Oloffs et al. (25), additive genetic variation
in the milk coagulation properties increased because
of the inclusion of the milk protein genotypes in the
model, which disagreed with the clear effect of the
genotypes on these properties.
Genetic correlations. The high genetic correla-
tion observed between the coagulation time and the
curd firmness (Table 5) was expected because these
parameters describe the consecutive steps of the milk
coagulation process. Except for pH and protein per-
centage, estimates for the genetic correlations be-
tween the milk coagulation properties and the milk
production traits were not reliable because of high
standard errors.
The unfavorable association between the milk
coagulation properties and high pH (Table 5) agreed
with some reported results (15, 25). The positive
correlation between protein percentage and coagula-
tion time and the negative correlation between pro-
tein percentage and curd firmness (Table 5) were
somewhat unexpected. The parallel changes in curd
firmness and protein percentage of milk with stage of
lactation (Table 3) implied an association between
high protein percentage and favorable milk coagula-
tion properties. Conversely, differences in the milk
coagulation properties and protein percentage be-
tween parity (Table 2), breed (Table 4), or b-k-CN
genotype classes (data not shown for protein percen-
tage) were more or less divergent. In addition, there
was no clear association between extreme breeding
values for curd firmness and breeding values for pro-
tein percentage (Table 7).
In the study of Oloffs et al. (25), genetic correla-
tions between the milk coagulation properties and
protein percentage could not be reliably estimated.
High casein percentage, however, was associated with
favorable milk coagulation properties (25), which
also emphasized the importance of casein in milk
coagulation. In contrast to the present results, Lind-
stro¨m et al. (15) reported that high protein and fat
percentages were correlated with short milk coagula-
tion times.
NC Milk
The NC milk found (12, 29) in the FAy breed in
the small Finnish data sets was observed also in the
data of the current study, in which 66 FAy cows (i.e.,
8%) produced NC milk. Extremely poorly coagulating
or NC milk, usually occurring in late lactation, had
been observed among Holstein (24) and Friesian
cows (4).
In the data of this study, there were 10 evaluated
FAy bulls that had at least 15 daughters and that
formed three families based on their mutual sire,
grandsire, or both (Table 7). In Family 1, the 2 bulls
with the largest daughter groups in the data were
closely related. A relatively large proportion of these
daughters produced NC milk. Among the bulls in
family 2, the proportions of daughters producing NC
milk were equal to or less than those among the bulls
in family 1; in family 3, there was only 1 bull having
2 daughters with NC milk. Consequently, 31 of the 66
cows with NC milk were descendants of the previous
7 bulls, which implies that genetic factors were par-
tially responsible for the occurrence of NC milk. The
rest of the cows with NC milk were daughters of 31
other bulls. These bulls were on average younger
than the previous 7 bulls and had fewer daughters
being milked at the time of the sample collection.
Journal of Dairy Science Vol. 82, No. 1, 1999
IKONEN ET AL.
212
TABLE 6. The 10 evaluated Finnish Ayrshire (FAy) bulls with at least 15 daughters.1
1Mutual pedigree (indicated by numbers) and information on curd firmness (CF) values of
daughters’ milk.
2Paternal grandsire.
3Maternal grandsire.
4Number of daughters.
5Proportion of daughters with a noncoagulating milk sample.
Bull
genotype for
k-CN
Pedigree Information on daughters
PGS2Mean Range
Sire MGS3n4%NC
5of CF of CF
Family 1
37465 1 31 29.0 17.6 0.0 to 40.0
EE 2
37505 2 79 14.0 15.5 0.0 to 48.0
AA 1
Family 2
36309 3 5 17 29.0 14.1 0.0 to 41.0
AE
36687 3 5 22 9.0 16.7 0.0 to 40.0
AA
36428 5 20 5.0 19.5 0.0 to 45.0
AA
36069 28 4.0 20.8 0.0 to 43.0
AE 3
Family 3
36378 4 6 15 13.0 19.9 0.0 to 34.0
AA 7
36310 4 6 24 0.0 22.0 1.0 to 44.0
AA 7
36299 4 6 16 0.0 33.6 9.0 to 49.0
AA
37154 6 20 0.0 23.2 9.0 to 39.0
AA
Five of the previous 7 bulls were homozygous for
the k-CN locus (Table 7). The bulls’ genotypes were
inferred from the genotypes of their daughters that
were included in this study and in the study of Ikonen
et al. (13). Among the daughters of the homozygous
bulls, the k-CN A, B, and E alleles were present; there
was no major difference in k-CN genotype frequencies
between the daughters producing NC milk and the
other daughters. This result implies that it was not
the k-CN gene but rather some other gene or genes
near the k-CN gene that were causing NC milk. Be-
cause there was great variation in the curd firmness
within the daughter groups of the 7 bulls (Table 7),
these bulls may be heterozygous for some of the
potential genes causing NC milk.
Additive Genetic Values
for the Curd Firmness
About 60% of the cows producing NC milk were
primiparous cows; their proportion in the whole data
set was 35%. Standardized (mean = 100, variation =
10) additive genetic values (EBV) for the curd firm-
ness of the 875 cows with records were examined to
determine whether there was any genetic trend in
that trait over the cow birth years 1983 to 1993. The
EBV estimated with Model [1] were used. Curd firm-
ness was chosen because it was the coagulation trait
for which each cow had an observation and for which
the heritability estimate was highest. In addition to
curd firmness, EBV for pH, milk yield, fat percentage,
protein percentage, and SCC were also studied.
The exact accuracies of the EBV were not calcu-
lated. Based on the heritability estimate for curd
firmness, the accuracy of the EBV for that trait would
be around 0.60 but was assumed to be somewhat
higher because of information on parents and grand-
parents of the cows with records. The accuracy of the
EBV for the other traits was of similar magnitude as
for the curd firmness.
No change was found in EBV for the curd firmness
for cows born during the period from 1983 to 1991,
but the cows born in 1992 and 1993 had, on average,
the lowest breeding values for the trait. In addition,
Journal of Dairy Science Vol. 82, No. 1, 1999
GENETIC PARAMETERS FOR MILK COAGULATION 213
TABLE 7. Breeding values for the 20 cows with the highest and the 20 cows with the lowest EBV for curd firmness (CF).
1Daily milk yield.
2F% = Fat percentage; P% = protein percentage.
3Phenotypic value for CF.
4k-CN Genotype.
Highest EBV Lowest EBV
Cow CF pH DMY1F%2P% SCC CFP3k-CN4Cow CF pH DMY F% P% SCC CFP k-CN
1 138 95 85 97 117 95 37.0 AB 856 70 120 85 106 112 86 0.0 AA
2 136 89 103 98 110 114 42.0 AB 857 70 118 93 94 117 93 3.0 AE
3 135 82 114 110 109 118 42.0 AB 858 70 158 81 112 137 106 0.0 AA
4 135 80 109 92 114 104 44.0 AB 859 69 98 85 97 103 98 0.0 AE
5 133 89 102 87 106 121 38.0 BE 860 69 118 106 89 100 108 1.0 AE
6 133 102 79 107 114 96 38.0 AB 861 69 82 107 102 104 93 0.0 AA
7 133 90 99 104 114 103 53.0 BE 862 69 137 124 86 97 123 0.0 AE
8 131 79 87 99 109 120 48.0 BE 863 69 93 94 97 94 91 0.0 AE
9 129 77 109 91 89 71 41.0 AB 864 68 136 95 103 115 136 0.0 AE
10 129 100 104 95 111 123 42.0 AB 865 68 136 97 77 90 120 0.0 EE
11 129 79 106 95 98 62 39.0 AA 866 68 124 104 88 85 139 0.0 EE
12 128 114 81 100 111 105 37.0 BE 867 68 116 108 94 98 107 4.0 AE
13 128 106 81 123 125 109 39.0 AB 868 67 108 99 109 109 86 0.0 AA
14 128 89 92 89 96 93 44.0 AB 869 67 131 97 87 81 136 8.0 EE
15 127 85 82 140 146 106 53.0 EE 870 67 121 111 81 95 118 0.0 AE
16 126 105 80 117 94 96 41.0 AB 871 66 91 109 106 95 84 1.0 AA
17 126 106 76 114 128 100 40.0 AA 872 64 94 94 70 95 81 0.0 AA
18 126 103 94 97 100 88 45.0 BB 873 64 132 111 89 101 116 0.0 EE
19 125 87 89 113 113 91 41.0 BE 874 62 178 77 98 116 114 0.0 AA
20 125 99 109 75 100 100 36.0 AB 875 60 121 100 82 97 114 0.0 AE
these cows had high breeding values for pH, low
values for fat percentage, but medium values for pro-
tein percentage.
All daughters of bull 37465 and majority of the
daughters of bull 37505 were born in 1992 or 1993.
Consequently, one-third of the cows born in these
years were daughters of the 2 previous bulls; the
proportion of other half-sib groups was ≤5%. Frequent
use of these 2 bulls, which had several daughters
producing NC milk, was one likely explanation for the
unfavorable genetic trend in the curd firmness for the
period from 1992 to 1993 in the present data.
Bulls 37465 and 37505 were extensively used in
the entire FAy population during the 1990s. Thus,
frequent use of these bulls, their sons, and other
relatives may have had an undesirable impact on the
genetic level of the milk coagulation properties in the
entire FAy population.
Breeding for Favorable Milk
Coagulation Properties
Based on the moderately high heritability esti-
mates for the milk coagulation properties there is
clear potential for genetic improvement of these
properties.
Out of the 20 cows with the highest EBV for curd
firmness, 17 had the k-CN AB, BB, or BE genotype;
the cows with the lowest EBV had the AA, AE, or EE
genotype (Table 7). Because determination of the
milk coagulation properties in the entire cow popula-
tion is not practical, these properties could be im-
proved indirectly by favoring the k-CN B allele.
One disadvantage of favoring the k-CN B allele
might be its association with low milk and protein
yields. Even though the k-CN B allele has no strong
effect on milk and protein yields in the FAy (11), it
occurs in linkage disequilibrium with the b-CN A1
allele, which has been strongly associated with low
milk and protein yields (11). However, in this study,
there was no clear difference in the breeding values
for milk yield between the cows with the highest
breeding values for the curd firmness and carrying
the k-CN B allele and the cows with the lowest breed-
ing values for the curd firmness and carrying the k-
CN A or E allele (Table 7).
Based on the estimates of the genetic correlations
between the milk coagulation properties and milk
production traits obtained in this study and in others
(15, 25), it is unclear whether the milk coagulation
properties would be improved by selecting for any
routinely recorded milk production trait.
CONCLUSIONS
Because of occurrence of NC milk in the FAy popu-
lation and the probability of an unfavorable trend in
Journal of Dairy Science Vol. 82, No. 1, 1999
IKONEN ET AL.
214
the milk coagulation properties, these traits should be
improved in the FAy. Because of the favorable effect
of the k-CN B allele on phenotypic and genetic values
for the curd firmness, the milk coagulation properties
could possibly be improved indirectly by favoring the
k-CN B allele.
ACKNOWLEDGMENTS
The authors thank the owners of the herds for the
help in collecting the milk samples, Food Research
Institute of Agricultural Research Centre (Jokioinen,
Finland) and Finnish Animal Breeding Association
(Vantaa, Finland) for laboratory facilities, and Anne
Lunde
´n for discussion of this manuscript. This work
was in part funded by the Ministry of Agriculture and
Forestry (Helsinki, Finland).
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