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Livestock Production Science 85 (2004) 27–34

Associations between milk protein genotypes and fertility traits

in Finnish Ayrshire heifers and first lactation cows

Outi Ruottinen*, Tiina Ikonen, Matti Ojala

Department of Animal Science, University of Helsinki, P.O. Box 28, FIN-00014 Helsinki, Finland

Received 2 May 2002; received in revised form 26 March 2003; accepted 18 April 2003

Abstract

Effects of composite h–n-casein genotypes and h-lactoglobulin genotypes on age at first insemination and length of service

period of 17,059 Finnish Ayrshire heifers, and on days from calving to first insemination and length of service period of 17,869

first lactation cows were estimated. A mixed linear model under an animal model was assumed. The effect of the h–n-caseingenotypes on days from calving to first insemination (DFI) was statistically significant. The difference in DFI between the rare

extreme h–n-casein genotypes A1A2BB and A1A2EE was about 19 days (0.75 phenotypic standard deviation), but the standard

errors of the effects of these genotypes were large. Between the most frequent h–n-casein genotypes the differences in DFI

were negligible. The other reproduction traits studied were not affected by composite h–n-casein genotypes or h-lactoglobulingenotypes. Based on the results presented in this study, selection based on h–n-casein and h-lactoglobulin polymorphism

should thus have no substantial impact on fertility of Finnish Ayrshire heifers and cows.

D 2003 Elsevier B.V. All rights reserved.

Keywords: Milk protein; Genotype; Reproduction; Finnish Ayrshire; Dairy cattle

1. Introduction

Several studies have established that the n-casein(n-CN) B-allele is associated with favourable milk

coagulation properties (Van den Berg et al., 1992;

Ikonen et al., 1997; Ikonen et al., 1999a) and high

protein, casein and n-casein contents in milk (Van den

Berg et al., 1992; Ikonen et al., 1997). The h-lacto-globulin (h-LG) B allele is associated with high fat

and casein contents, and high casein number in milk,

0301-6226/$ - see front matter D 2003 Elsevier B.V. All rights reserved.

doi:10.1016/S0301-6226(03)00123-4

* Corresponding author. Tel.: +358-50-3594509; fax: +358-9-

19158379.

E-mail address: outi.ruottinen@reppu.net (O. Ruottinen).

and the A allele with high protein production (Boven-

huis et al., 1992; Van den Berg et al., 1992; Hill 1993;

Ikonen et al., 1997; Ikonen et al., 1999b). Because of

the above associations between the n-CN B and h-LGB alleles and coagulation properties and protein com-

position of milk, these alleles could be favoured in

selection in order to genetically improve cheese mak-

ing properties of milk. Before milk protein genes can

be used as a selection criterion in breeding, their

effects on all important traits of dairy cattle have to

be established.

Besides milk production, fertility traits are biolog-

ically and economically important. In 1998, fertility

disorders accounted for 27% of the different disease

groups in Finnish dairy cows (The Finnish Animal

O. Ruottinen et al. / Livestock Production Science 85 (2004) 27–3428

Breeding Association, Vantaa, Finland). In addition,

every fifth cow was culled because of poor fertility

(Association of Rural Advisory Centers, Helsinki,

Finland). Because poor fertility can cause substantial

economic losses to milk producers, it is important to

know the association between milk protein polymor-

phism and fertility, and how selection for certain milk

protein genotypes would affect fertility of dairy cows.

In general, it is rather complicated to study fertility

of dairy animals, because it can be described by

various reproduction traits, such as days open, days

from calving to first insemination, non-return rate, and

number of services per conception. In addition, be-

cause variation in the reproduction traits is mostly due

to various environmental factors (Janson 1980a; Man-

tysaari and VanVleck, 1989; Hodel et al., 1995),

heritability estimates for these traits are low, ranging

from 0.01 to 0.06 (Janson 1980b; Weller 1989; Hayes

et al., 1992; Hoekstra et al., 1994; Hodel et al., 1995;

Weigel and Rekaya, 2000). Large data and accurate

recording of the reproduction traits are thus needed for

reliable estimation of associations between milk pro-

tein polymorphism and reproduction traits.

The literature dealing with the associations be-

tween milk protein polymorphism and fertility of

dairy cows is limited (Hargrove et al., 1980, Lin et

al., 1987, Lin et al., 1992, Panicke et al., 1998). In

addition, because the effects of the milk protein

genotypes on fertility traits have been estimated by

use of rather small data and different statistical meth-

ods and models, the results for the milk protein

genotype effects on these traits are inconsistent.

Because mixed model procedures under an animal

model can distinguish single gene effects from those

of the other polygenes (Kennedy et al., 1992), use of

these methods to estimate the effects of milk protein

polymorphism on quantitative traits is reasonable. In

addition, the casein loci are located close to one

another on chromosome 6 (Ferretti et al., 1990;

Threadgill and Womack, 1990), and linkage disequi-

librium exists between these loci (Bovenhuis et al.,

1992; Ikonen et al., 1999b). An appropriate way to

estimate the effects of casein genotypes is thus to use

composite casein genotypes or casein haplotypes

(Ojala et al., 1997; Ikonen et al., 1999b; Ikonen et

al., 2001).

The objective of this study was to estimate the

effects of the h–n-casein (h–n-CN) and h-lactoglob-

ulin (h-LG) genotypes on reproduction traits of Finn-

ish Ayrshire (FAy) heifers and first lactation cows.

2. Material and methods

2.1. Data

2.1.1. Original data

A total of 20,928 Finnish Ayrshire (FAy) cows

from 1688 herds were genotyped for the major milk

proteins (as1-, as2-, h-, and n-caseins, and h-lacto-globulin) by isoelectric focusing in polyacrylamide

gels as described by Erhardt (1989). Collection and

structure of the data have been previously described

(Ikonen et al., 1999b). The heifer and first lactation

reproduction traits of the cows genotyped for the milk

proteins were calculated using information on dates of

birth, inseminations and calving, and information on

the success of each insemination. This information

was obtained from the official milk recording database

from the Agricultural Data Processing Centre (Vantaa,

Finland). A total of 15,516 cows had records for both

heifer and first lactation fertility.

2.1.2. Heifer fertility data

The traits chosen to describe heifer fertility were

age at first insemination (AFI) in days, and length of

the service period (SPH) in days. Service period was

defined as the period between the first insemination

and conception. Because 66% of the heifers had

conceived at the first service, and had the same value

for AFI and age at conception, the latter trait was

excluded from the statistical analyses. Furthermore,

both SPH and number of services per conception

describe heifers’ ability to conceive. Only SPH was

used in the statistical analyses because it had a more

continuous distribution and larger variation than had

number of services per conception. Because the dis-

tribution for SPH was far from normal, it was loga-

rithmically transformed.

Only the heifers that had realistic values for AFI

(180–810 days), SPH (0–360 days), as well as for

age at conception (180–810 days), gestation length

(240–310 days), and age at calving (450–1081 days)

were included in the final data. Unrealistic values for

these traits may have resulted from false recording of

birth, insemination or calving dates. In addition, the

O. Ruottinen et al. / Livestock Production Science 85 (2004) 27–34 29

44 heifers that carried one of the rare h–n-CNgenotypes (A1BAE, A2BAA, or A2A2AE), and the

herds with less than four heifers were excluded from

the final data. After these restrictions, the heifer

fertility data included 17,059 heifers from 1527 herds.

The heifers were born during a period from 1985 to

1993, and were daughters of 695 FAy sires. The

average number of heifers per herd was 11, and it

ranged from four to 34.

2.1.3. First lactation fertility data

The traits chosen to describe first lactation fertility

were the period from calving to the first insemination

(DFI) in days, and length of service period (SPC) in

days. Because 48% of the cows conceived at the first

service, and had the same value for DFI and days

open, inclusion of days open in the final data was

unnecessary. Because the distribution for SPC was not

normal, it was logarithmically transformed.

The first lactation cows that had realistic values for

DFI (30–360 days), SPC (0–360 days), days open

(30–360 days), and gestation length (240–310 days)

were included in the final data. Because the first

lactation cows were required to have a second calving,

the cows that were culled during the first lactation

were excluded from the data. The 50 cows that carried

one of the rare h–n-CN genotypes (A1BAE, A2BAA,

or A2A2AE) were excluded from the final data. In

addition, the first lactation cows were required to have

a record for the 305-day milk yield. The minimum

herd size was required to be five.

Acceptable records for the first lactation reproduc-

tion and milk production traits were obtained for

17,869 cows from 1521 herds. The cows were born

during a period from 1984 to 1993, and they were

daughters of 745 FAy sires. The average number of

cows per herd was 12, and it ranged from five to 37.

2.2. Statistical analyses

Effects of the h–n-CN and h-LG genotypes on the

reproduction traits of the heifers and first lactation

cows were estimated using the following univariate

mixed linear model:

y ¼ Xb þ Qg þ Za þ e; ð1Þwhere y is a vector of observations for a heifer or a

first lactation reproduction trait, b is a vector of fixed

environmental effects, g is a vector of fixed effects

of the h–n-CN genotypes and the h-LG genotypes,

c is a vector of random herd effects (0, IS2c), a is a

vector of random additive genetic effects of animals

(0, AS2a ), and e is a vector of random residual effects

(0, IS2e).

X, Q, H and Z were known incidence matrices

relating observations in y to the classes of vectors b,

g, c and a. A was the additive relationship matrix

among the animals in a. The pedigree of the heifers

and the first lactation cows with records included their

parents and grandparents. The total number of animals

included in the statistical analyses was 38,785 for the

heifers and 40,111 for the first lactation cows.

For AFI, the fixed environmental effects in model

(1) were birth year and birth month, and for SPH

service year and service month. Birth year was

grouped into six classes: 1985–1987, 1988, 1989,

1990, 1991, and 1992–1993, and service year into six

classes: 1987–1988, 1989, 1990, 1991, 1992, and

1993–1994. Birth month and service month were

both grouped into 12 classes according to the calendar

months.

For DFI, the fixed environmental effects in model

(1) were calving year and calving month, and for SPC

service year and service month. Calving year was

grouped into seven classes: 1986–1988, 1989, 1990,

1991, 1992, 1993, and 1994, and service year into

eight classes: 1987–1988, 1989, 1990, 1991, 1992,

1993, 1994, and 1995. Calving month and service

month were both grouped into 12 classes according to

the calendar months.

Effects of the h-CN and n-CN genotypes on the

reproduction traits were estimated by use of compos-

ite h–n-CN genotypes. Because as1-CN and as2-CN

were almost monomorphic, they were excluded from

the composite casein genotypes. Composite h–n-CNconsisted of 14 genotype classes (Table 1). The

number of cows (and observations) as well as the

number of sires and paternal grandsires of the cows

varied considerably between the h–n-CN genotype

classes (Table 1). h-LG included three genotype

classes: AA, AB, and BB.

In addition to the univariate analyses, effects of the

h–n-CN genotypes and h-LG genotypes on the

reproduction traits of the first lactation cows were

estimated by use of a trivariate model (2), where DFI

and SPC were analysed together with first lactation

Table 1

The number of sires and paternal grandsires, and the number of

daughters per sire and grandsire in h–n-CN genotype classes in

Finnish Ayrshire first lactation cows

h–n-CN N NS NGS ND/S ND/GS

X Max% X Max%

A1A1AA 384 119 52 3 14 7 22

A1A1AB 404 144 53 3 9 8 10

A1A1AE 1451 305 72 5 10 20 16

A1A1BB 68 38 23 2 18 3 19

A1A1BE 704 218 61 3 8 12 10

A1A1EE 1581 288 68 6 7 23 15

A1A2AA 2216 412 75 5 6 30 13

A1A2AB 1239 334 73 4 7 17 10

A1A2AE 5431 580 87 9 3 62 10

A1A2BB 34 21 11 2 15 3 56

A1A2BE 104 51 26 2 10 4 36

A1A2EE 24 20 15 1 17 2 17

A2A2AA 3994 490 79 8 3 51 9

A2A2AB 235 100 37 2 9 6 37

N, number of observations; NS, number of sires; NGS, number of

grandsires; ND/S, number of daughters per sire; ND/GS, number of

daughters per grandsire; X, average number of daughters per sire or

granddaughters per grandsire in a genotype class; Max%, the largest

daughter or granddaughter group as a fraction of the total number of

observations in a genotype class.

O. Ruottinen et al. / Livestock Production Science 85 (2004) 27–3430

milk yield. This model was used to determine whether

information on the genetic correlations between milk

yield and DFI and SPC would change the effects of

the milk protein genotypes on these traits. In model

(2), the fixed environmental effects (vector b) for

milk yield were calving year and calving month

grouped in the same way as for DFI in model (1),

and age at calving. Age at calving was grouped into

Table 2

Means and variation of the reproduction traits in Finnish Ayrshire heifers

Trait Mean

Heifers (N= 17,059):

Age at first insemination, days 481

Service period, daysa 16

Service period, lnb 1.2

First lactation cows (N = 17,869):

Days from calving to first insemination 79

Service period, daysa 28

Service period, lnb 1.9

a Untransformed records.b Logarithmically (ln) transformed records.

10 classes. Except for the first ( < 660 days) and last

(>900 days) class, age at calving was grouped at 30-

day intervals. Other factors in model (2) were as

described in model (1). Herd, animal and residual

effects were treated as random with zero mean and

with var(c) = I�H0, var(a) = A�G0, and var(-

e) = I�R0, where H0, A0 and R0 are 3� 3 (co)vari-

ance matrices for the herd, animal, and residual

effects across the three traits.

Variance and covariance components for the addi-

tive genetic, herd, and residual effects were estimated

by use of the REMLVCE-package 4.0 (Neumaier and

Groeneveld, 1998). Solutions for the fixed and ran-

dom effects in the models were estimated by use of

the PEST-package (Groeneveld, 1990). Statistical sig-

nificance of the overall effect of the fixed effects was

tested using the F test provided by the PEST-package.

The null hypothesis tested was KVb = 0, where KVbcontained all independent estimable contrasts between

classes of a fixed effect.

3. Results

3.1. Means and variation

Means and variation of the reproduction traits in

Finnish Ayrshire heifers and first lactation cows are

presented in Table 2. Because the heifers were re-

quired to have information on the first calving, and

the first lactation cows on the second calving, the

heifers and the first lactation cows that had not

conceived were excluded from the data. The actual

and first lactation cows

S.D. Min Max

62 264 792

30 0 255

1.8 0 5.5

25 31 329

40 0 317

2.0 0 5.8

Table 3

Variance components for the random effects of the reproduction traits in Finnish Ayrshire heifers and first lactation cows, expressed as a fraction

of the total phenotypic variance

Trait r2a (S.E.) r2

c (S.E.) r2e (S.E.)

Heifers

Age at first insemination 0.02 (0.01) 0.36 (0.01) 0.61 (0.01)

Service perioda 0.02 (0.01) 0.02 (0.003) 0.96 (0.01)

First lactation cows

Days from calving to first insemination 0.04 (0.01) 0.17 (0.01) 0.79 (0.01)

Service perioda 0.02 (0.01) 0.02 (0.003) 0.95 (0.01)

r2a , additive genetic variance relative to phenotypic variance, i.e. estimate of heritability; r2c, herd variance relative to phenotypic variance; r2e,

residual variance relative to phenotypic variance; S.E., standard error of the ratios.a Logarithmically (ln) transformed.

O. Ruottinen et al. / Livestock Production Science 85 (2004) 27–34 31

fertility level of the FAy heifers and first lactation

cows was thus somewhat lower than that observed in

this study.

3.2. Effects of environmental factors

3.2.1. Birth, service, and calving year

In the heifers, AFI varied considerably between the

birth year classes, and SPH between the service year

Table 4

Estimates (Est.) for the effects of h–n-CN and h-LG genotypes on repro

Genotype Heifers AFI (X = 481) SPH (X= 1.2)

NEst. S.E. Est. S.E

h–n-CNA1A1AA 370 2.5 2.7 0.07 0.1

A1A1AB 381 1.1 2.7 � 0.01 0.1

A1A1AE 1402 1.3 1.6 � 0.02 0.0

A1A1BB 66 � 4.9 6.1 � 0.09 0.2

A1A1BE 667 2.7 2.1 0.03 0.0

A1A1EE 1527 2.0 1.6 0.06 0.0

A1A2AA 2154 1.5 1.4 0.08 0.0

A1A2AB 1171 � 0.4 1.7 � 0.07 0.0

A1A2AE 5144 0.4 1.1 0.04 0.0

A1A2BB 29 � 4.3 9.2 0.31 0.3

A1A2BE 102 � 9.5 5.0 � 0.13 0.1

A1A2EE 19 3.5 11.2 � 0.67 0.4

A2A2AA 3803 0 0

A2A2AB 224 2.3 3.5 � 0.16 0.1

F-test 0.651 0.280

h-LGAA 1345 � 3.0 1.5 � 0.08 0.0

AB 7025 � 0.9 0.8 0.02 0.0

BB 8689 0 0

F-test 0.130 0.157

AFI, age at first insemination (days); SPH, service period of heifers (day

insemination (days); SPC, service period of cows (days), logarithmically (ln

estimate.

classes (for both, P < 0.001). No clear trend existed,

however, in these variations. A yearly variation was

observed also in the first lactation fertility traits, but

the differences in DFI (P < 0.001) and SPC (P < 0.01)

between the years were rather small.

3.2.2. Birth, service, and calving month

The heifers that were born in the spring (from

March to June) were 34–46 days older at first

duction traits of Finnish Ayrshire heifers and first lactation cows

Cows DFI (X= 79) SPC (X= 1.9)

.N

Est. S.E. Est. S.E.

0 384 2.1 1.3 0.06 0.11

0 404 0.5 1.3 0.03 0.10

6 1451 1.3 0.8 0.10 0.06

2 68 � 5.2 2.9 0.23 0.24

8 704 � 0.7 1.0 0.06 0.08

6 1581 � 0.3 0.7 0.14 0.06

5 2216 � 0.4 0.6 0.06 0.05

6 1239 � 2.2 0.8 0.04 0.06

4 5431 � 0.2 0.5 0.10 0.04

3 34 � 12.4 4.1 � 0.18 0.34

8 104 4.7 2.4 0.27 0.20

0 24 6.4 4.8 0.35 0.40

3994 0 0

2 235 0.1 1.6 � 0.01 0.13

< 0.001 0.594

5 1406 0.2 0.7 � 0.03 0.06

3 7358 � 0.2 0.4 0.04 0.03

9105 0 0

0.751 0.273

s), logarithmically (ln) transformed; DFI, days from calving to first

) transformed; N, number of observations; S.E., standard error of the

O. Ruottinen et al. / Livestock Production Science 85 (2004) 27–3432

insemination (AFI) than were those born in Novem-

ber or December (P < 0.001). For SPH, the lowest

values were obtained for the heifers that were

inseminated in December or in May, and the highest

values for those inseminated in February, March or

August (P < 0.001).

The effect of service month on the service period

of the first lactation cows (SPC) differed slightly

from that of the heifers; SPC was shortest for the

cows that were inseminated in the summer (from

June to August), and longest for those inseminated in

February (P < 0.001). The cows that calved in May

or June had the lowest values for DFI, and those that

calved in March, July or August had the highest

(P < 0.001).

3.2.3. Herd

The herd effect explained 36% of the phenotypic

variation in AFI, and 17% of that in DFI (Table 3).

The effect of herd on the service period of the heifers

and the first lactation cows was weak; only 2% of the

phenotypic variation in these traits was due to the herd

effect.

3.3. Effects of the milk protein genotypes

The h–n-CN genotypes had no statistically signif-

icant effect on AFI or SPH (Table 4). In the first

lactation cows, the h–n-CN genotypes were not

associated with SPC, but the effect of these genotypes

on DFI was statistically significant (Table 4). The few

cows that carried h–n-casein genotype A1A1BB

(N = 68) or A1A2BB (N = 34) had the lowest values

for DFI, and those that carried A1A2BE (N = 104) or

A1A2EE (N = 24) had the highest. The difference in

DFI between the extreme h–n-CN genotypes was

about 19 days. Between the most frequent composite

genotypes the differences in DFI were small. The h-LG genotypes had no statistically significant effect on

the fertility traits of the heifers or the first lactation

cows.

The genetic correlations between milk yield and

DFI (0.23F 0.07) and milk yield and SPC (0.45F0.08) were moderate. When the first lactation repro-

duction traits were analysed simultaneously with

milk yield [model (2)], the effect of the h–n-CNgenotypes on DFI or SPC changed only slightly, if

any.

4. Discussion

4.1. Environmental factors

Because many environmental factors, such as sea-

son and herd, play an important role in the total

variation of reproduction traits, the additive genetic

effects account for a small portion of this variation.

The low heritability estimates for the reproduction

traits of the heifers and the first lactation cows

obtained in this study agree well with some of those

presented in the literature (Janson 1980b; Weller

1989; Hayes et al., 1992; Hoekstra et al., 1994; Hodel

et al., 1995; Weigel and Rekaya, 2000), but were

lower than those presented by Mantysaari and VanV-

leck (1989), and Raheja et al. (1989).

4.2. Milk protein genotypes

In this study, the h–n-CN and h-LG genotypes

were not associated with the reproduction traits of the

heifers. According to Lin et al. (1987), the h-CN and

n-CN loci had no statistically significant additive or

dominance effects on the reproduction traits of 890

heifers. Furthermore, the h-LG genotypes had no

significant effect on age at first breeding of the

heifers, but the heifers with the h-LG AB genotype

were younger at conception and had a shorter service

period than those with h-LG AA or BB genotype (Lin

et al., 1987).

In the present study, a statistically significant

association existed between the h–n-CN genotypes

and DFI, but no association between these genotypes

and SPC. The h-LG genotypes had no statistically

significant effect on DFI or SPC. These findings

disagree, in part, with those presented by Hargrove

et al. (1980) and Panicke et al. (1998). According to

Hargrove et al. (1980), the h-CN, n-CN and h-LGgenotypes had no effect on days open in 6000

Holstein cows. According to Panicke et al. (1998),

the casein genotypes had no statistically significant

effect on DFI in 984 German Black Pied cows. The

h-CN A1A2 and n-CN AA genotypes had, however,

a statistically significant favourable effect on days

open, and on number of inseminations per pregnan-

cy. Furthermore, the n-CN and h-LG genotypes had

a statistically significant joint effect on days open,

and the n-h-as1-CN genotype combinations includ-

O. Ruottinen et al. / Livestock Production Science 85 (2004) 27–34 33

ing n-CN AB, h-CN A1A2 and as1-CN BC geno-

types had a favourable effect on days open (Panicke

et al., 1998).

The association between h-n-casein genotypes and

DFI observed in the present study should be consid-

ered with caution. The data of this study were unbal-

anced, i.e. the observations were quite unequally

distributed in the h–n-casein genotype classes. The

magnitude of the difference between the extreme

genotypes A1A2BB and A1A2EE in DFI was 0.75

phenotypic standard deviation, but these genotype

classes had the lowest numbers of observations (34

and 24). Consequently, the standard errors of the

effects of these genotypes were large. The associa-

tions between DFI and the h–n-casein genotypes witha reasonable number of observations were generally

negligible.

The h–n-casein genotypes A1A1BB and A1A2BB,

which were associated with the shortest values for

DFI, were also associated with the lowest values for

milk yield [model (2), data not shown]. Because of the

moderate antagonistic genetic associations between

fertility traits and milk yield observed in this study

and in the literature (Hoekstra et al., 1994; Hodel et

al., 1995; Poso and Mantysaari, 1996), it is possible

that the low values for DFI for genotypes A1A1BB

and A1A2BB were partly due to low milk production.

When DFI and first lactation milk yield were analysed

simultaneously [model (2)], the effects of genotypes

A1A1BB and A1A2BB on DFI changed, however,

only slightly, if any.

Because of linkage disequilibrium, effects of gen-

otypes of single genes may be confounded with

polygenic effects if animals sharing the same genes

are descendants of a common sire. In this case, an

animal model may not be able to distinguish the single

gene effects from the polygenic effects, and estimates

of the genotype effects of the genes may be biased.

Even though the number of sires varied among the h–n-CN genotypes, the average number of daughters per

sire was small in each h–n-CN genotype (Table 1). In

the rare h–n-CN genotype A1A2BB, which was

associated with the lowest values for DFI, 56% of

the cows descended from a common grand sire, which

could have impeded reliable estimation of the effect of

this genotype.

The h-CN and n-CN genes would show an asso-

ciation with reproduction traits if these genes them-

selves affect fertility, or if they are closely linked with

quantitative trait loci (QTL) affecting fertility. Some

putative QTL have been found on chromosomes 7 and

23 that affect ovulation rate (Blattman et al., 1996),

and on chromosome 4 that affect gestation length

(Schrooten et al., 2000). No QTL affecting fertility

of dairy cattle have yet been reported on chromosome

6, where the casein genes are located (Ferretti et al.,

1990; Threadgill and Womack, 1990), or on chromo-

some 11, where the h-LG gene is located (Eggen and

Fries, 1995).

5. Conclusions

The results of this study indicate that the h–n-CNand h-LG genotypes have no strong effect on repro-

duction traits of FAy heifers or first lactation cows.

Consequently, selection based on h–n-casein and h-lactoglobulin polymorphism should have no substan-

tial impact on fertility of Finnish Ayrshire heifers and

cows.

6. Notation

FAy, Finnish Ayrshire

AFI, age at first insemination

SPH, service period of heifers

DFI, days from calving to first insemination

SPC, service period of cows

CN, casein

LG, lactoglobulin

QTL, quantitative trait locus

Acknowledgements

The authors wish to express their appreciation to

the owners of the herds and to the dairy co-operative

Promilk (Lapinlahti, Finland) and Valio Ltd. (Helsin-

ki, Finland) for their assistance in collecting the milk

samples, Finnish Animal Breeding Association (Van-

taa, Finland) for the laboratory facilities, and Tapani

Hellman from the Agricultural Data Processing Centre

(Vantaa, Finland) for providing the data. This work

was partly funded by the Finnish Ministry of

Agriculture and Forestry (Helsinki, Finland), and by

O. Ruottinen et al. / Livestock Production Science 85 (2004) 27–3434

a grant from the Foundation of August Johannes and

Aino Tiura (Finland) for the first author.

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