Inbreeding effects on postweaning production traits, conformation, and calving performance in Irish...

S. Mc Parland, J. F. Kearney, D. E. MacHugh and D. P. Berryperformance in Irish beef cattle

Inbreeding effects on postweaning production traits, conformation, and calving

published online August 1, 2008J ANIM SCI

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Inbreeding depression in Irish beef cattle1

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Inbreeding effects on postweaning production traits, conformation, and calving 3

performance in Irish beef cattle4

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S. Mc Parland*,§,1, J. F. Kearney†, D. E. MacHugh§, and D. P. Berry*6

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* Teagasc, Moorepark Dairy Production Research Centre, Fermoy, Co. Cork, Ireland.8

§ Animal Genomics Laboratory, School of Agriculture, Food Science and Veterinary9

Medicine and Conway Institute for Biomolecular and Biomedical Research, College of 10

Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland.11

†Irish Cattle Breeding Federation, Bandon, Co. Cork, Ireland.12

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1Corresponding Author: Sinéad Mc Parland, Teagasc, Moorepark Dairy Production 17

Research Centre, Fermoy, Co. Cork, Ireland.18

Tel: +353 25 42647 Fax: +353 25 42310.19

Email: [email protected]

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Page 1 of 31 Journal of Animal Science

Published Online First on August 1, 2008 as doi:10.2527/jas.2007-0751 by guest on May 18, 2011jas.fass.orgDownloaded from


ABSTRACT: The objective of this study was to quantify the effect of inbreeding on

carcass quality, growth rate, live conformation measures, and calving performance in

purebred populations of Charolais, Limousin, Simmental, Hereford, and Angus beef

cattle using data from Irish commercial and pedigree herds. Variables analyzed are

reflective of commercial farming practices. Inbreeding was included in a linear mixed

model as either a class variable or a linear continuous variable. Non-linear effects were

non-significant across all traits. Inbred animals had lower carcass weight and less carcass

fat. The effects of inbreeding were more pronounced in the British beef breeds. Effects

for carcass weight ranged from -0.87 kg (Charolais) to -1.90 kg (Hereford) per 1%

increase in inbreeding. Inbred Charolais and Hereford animals were younger at slaughter

by 3 and 5 d, respectively, per percent increase in inbreeding, while the effect of

inbreeding on age at slaughter differed significantly with animal gender in the Limousin

and Angus breeds. Inbred Limousin and Angus heifers were younger at slaughter by 5

and 7 d, respectively per percent increase in inbreeding. Continental animals were more

affected by inbreeding for live muscling and skeletal conformational measurements than

the British breeds; inbred animals were smaller and narrower with poorer developed

muscle. Calf inbreeding significantly affected perinatal mortality in Charolais,

Simmental, and Hereford animals. The effects were dependent upon dam parity and calf

sex; however, where significant the association was always unfavorable. Dam inbreeding

significantly affected perinatal mortality in Limousin and Hereford animals. Effects

differed by parity in Limousins. Inbred first parity Angus dams had a greater incidence of

dystocia. Although the effects of inbreeding were sometimes significant, they were small

Page 2 of 31Journal of Animal Science



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and are unlikely to make a large financial impact on commercial beef production in

Ireland.

Key words: beef cattle, calving performance, carcass, growth, inbreeding depression

INTRODUCTION

Inbreeding occurs when related individuals are mated and is defined as the

probability that two alleles at any locus are ‘identical by descent’ (Falconer and Mackay,

1996). Inbreeding depression refers to the reduction in mean phenotypic performance as a

result of inbreeding. The effects of inbreeding on production traits of beef and dairy cattle

have been well documented (MacNeil et al., 1989; Smith et al., 1998; Mc Parland et al.,

2007a). However, the majority of studies on the effects of inbreeding in beef populations

is dated and generally involves experimental herds, thus is not entirely representative of

real populations (Dinkel et al., 1968; Krehbiel et al., 1969; MacNeil et al., 1989).

The effects of inbreeding on pre-weaning production (Keller and Brinks, 1978),

production up to 1 yr of age (Nelms and Stratton 1967) and varying definitions of cow

fertility (MacNeil et al., 1989) have previously been reported in beef cattle. However, the

effect of inbreeding on carcass quality, animal conformation and calving performance,

particularly in relation to beef animals, is less well documented. A review of the literature

on the effects of inbreeding in beef cattle detailed only linear effects (Burrow, 1993).

However, inbreeding has been shown to have non-linear effects on production traits in

dairy cattle (Croquet et al., 2006), as well as weaning traits in beef cattle (Dinkel et al.,

1968). Furthermore, Burrow (1993) reported a paucity of information concerning the




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effect of inbreeding on some economically important traits in beef cattle. Few studies

(Burrow, 1998; Gengler et al., 1998; Pariacote et al., 1998) have since been published;

consequently these economically important traits have yet to be fully addressed.

Beef is of major economic importance to Ireland (Central Statistics Office, 2006).

Furthermore, inbreeding in some beef breeds in Ireland is rising (Mc Parland et al.,

2007b). Hence quantification of the effects of accumulation of inbreeding in Irish beef

populations is important. Therefore, the objective of this study was to quantify the effect

of inbreeding on carcass quality, live measures, and calving performance in the largest

purebred beef cattle populations in Ireland.

MATERIALS AND METHODS

Data Description

Pedigree information on 183,495 Charolais, 110,546 Limousin, 91,018

Simmental, 56,229 Hereford, and 60,288 Angus purebred animals was extracted from the

Irish Cattle Breeding Federation database. Purebred animals were defined as ≥87.5% of

the breed in question (Mc Parland et al., 2007b). Inbreeding coefficients (F) were

calculated using the Meuwissen and Luo (1992) algorithm with a base year set to 1960

for all animals. Production and performance records were retained only for animals with

a minimum of 3 complete generations of pedigree information. Records include those

from both commercial herds and breeding herds. A description of traits analyzed is given

in Table 1. DAF (2004) provide a more detailed description of carcass measures.

Carcass Measures. Because the majority of slaughtered animals in Ireland are

crossbred (DAF, 2007), there was a lack of carcass data on pedigree animals in Ireland.




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Nonetheless, carcass data (n = 1,748,894) pertaining to carcass gender (i.e., heifer, steer,

bull), carcass weight, fat score, and conformation score from 9 Irish commercial

slaughter plants were obtained from the Irish Cattle Breeding Federation database for

animals slaughtered between 2000 and 2006, inclusive. Carcass fat score and

conformation score were transformed to a scale of 1 to 15 as outlined by Hickey et al.

(2007). Average daily carcass gain (ADCG) was computed as carcass weight per day of

age.

Records of twins were excluded from the analyses, as were records from any

animal that had moved herds > 3 times during its lifetime, or where either the

identification number of the herd immediately prior to slaughter or the identification

number of the slaughter plant was missing. Only data from animals slaughtered between

365 and 1,095 d of age were retained. Furthermore, animals with an ADCG 3 or more SD

from the mean within gender by breed were removed (Hickey et al., 2007).

Contemporary groups of herd-year-season of birth and herd-year-season of slaughter

were created, whereby season represented month of birth or slaughter grouped into 2

monthly intervals and herd represented the herd in which the animal was born or was

kept immediately prior to slaughter.

After edits, 4,969, 2,365, 771, 950, and 845 carcass records were available for the

Charolais, Limousin, Simmental, Hereford, and Angus breeds, respectively.

Live Measures. Live measures were assessed subjectively on a linear scale by

trained classifiers (ICBF, 2007). Traits scored included the muscling traits of loin

development, hindquarter development, width at withers, width behind withers, width at

hips, and depth of rump; the skeletal traits of bone development, length of back, length of




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pelvis, and height at withers; as well as scrotum circumference, conformation score,

locomotion, and docility (ICBF, 2003). The muscling traits of loin development,

hindquarter development, width at withers, and width behind withers, were scored on a

scale of 1 to 15, while all other traits were scored from 1 to 10 (Table 2). Data were

edited to include only the first observation in time of animals between 200 and 600 d of

age, where animals were scored between 1996 and 2006, inclusive. Contemporary groups

of herd-year-season of classifier visit were formed, whereby season represented the

month of scoring grouped into 3 monthly intervals. Only contemporary groups with at

least 3 records were retained. After edits, the data sets for the Charolais, Limousin,

Simmental, Hereford, and Angus breeds contained 30,345, 30,881, 3,125, 1,655, and 757

records, respectively.

Calving Measures. Calving performance data consisting of incidence of perinatal

mortality, dystocia, twinning, and calf sex were extracted from the Irish Cattle Breeding

Federation database for cows calving between 2000 and 2006, inclusive. Records for

pedigree animals were isolated from this data set and edited as previously described for

dairy cattle by Mc Parland et al. (2007a). Two separate datasets were constructed for each

breed and were edited and analyzed separately. The first data set was used to quantify the

effect of dam inbreeding on the calving performance of the dam, while the second data

set was used to investigate the effect of calf inbreeding on the calving performance of the

dam. Dystocia is recorded in Ireland on a scale from 1 to 4 and was categorized as 0 (no

assistance) and 1 (assistance required). This is similar to the recording scheme

recommended by ICAR (2007) disregarding the class “Embryotomy”. Perinatal mortality

was defined as 0 (no perinatal mortality occurred) or 1 (perinatal mortality occurred).




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Contemporary groups of herd-year of calving were constructed and only contemporary

groups with ≥3 records were included in the analyses. After edits, 61,881, 42,142, 4,629,

15,736, and 17,441 dam records were available for Charolais, Limousin, Simmental,

Hereford, and Angus, respectively, in the first data set. After separate editing, 67,465,

43,958, 8,833, 17,026, and 18,449 calf records were available for Charolais, Limousin,

Simmental, Hereford, and Angus, respectively, in the second data set. The breakdown of

these records according to parity is provided in Table 3.

Analysis

Inbreeding depression was quantified for each breed separately. All analyses were

undertaken in ASREML (Gilmour et al., 2006) using an animal model for the carcass and

live traits and a sire-maternal grandsire model for the calving performance traits.

Fixed effects included in the models were based on biological plausibility, as well

as the statistical significance of the effect in the model based on the F-test. Models to

analyze carcass weight, carcass fat score, and carcass conformation included the fixed

effects of slaughter plant and animal gender, while the models to analyze ADCG and age

at slaughter also included the fixed effects of year of slaughter, season of slaughter

(spring, summer, autumn, and winter), and age of dam at birth of animal (missing, ≤3 yr,

3< yr ≤6, >6yr). All models included the random effects of animal and herd-year-season

of birth. When the dependent variable was carcass weight, fat or conformation, herd-

year-season of slaughter was also included as a random effect. Herd-year-season was

included as a random effect due to the small size of data sets and thus the small number

of records per contemporary group.




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Models to analyze live measures included the quadratic effect of age at scoring in

a two-way interaction with sex, age of dam at calving, and contemporary group of herd-

year-season of visit as fixed effects, as well as the random effect of animal.

Models to analyze perinatal mortality, dystocia, and twinning included the fixed

effects of herd-year of calving, age of dam deviated within parity by dam parity, sex of

calf by dam parity, and year of calving by month of calving. The correlation between the

inbreeding level of the dam and that of the calf was tested and subsequently the

inbreeding coefficients of both the dam and the calf were included in all calving

performance models as fixed effects. Random effects were the permanent environmental

effect of the dam, and the sire and maternal-grandsire genetic effects. A covariance was

fitted between sire and maternal-grandsire components for the analysis of dystocia.

Inbreeding was included in all models as a linear effect with the presence of a

curvilinear effect also tested for statistical significance. Significance thresholds were set

at P<0.001 for higher order polynomials to avoid type II errors due to multiple testing. In

a separate series of analyses inbreeding was also included as a class variable (F=0,

0<F≤6.25, 6.25<F≤12.5, 12.5<F≤25, F>25). It was considered that a low number of

highly inbred animals could bias the results where inbreeding was treated as a continuous

variable. Thus, inbreeding effects from when it was treated as a continuous or a class

variable were compared. Comparison of inbreeding effects between inbreeding classes

was only undertaken when the main effect was significant (P<0.05). Interactions between

inbreeding and animal sex were tested in all cases as were interactions between

inbreeding and dam parity tested in all calving performance analyses (P<0.05).




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RESULTS AND DISCUSSION

Mean inbreeding for each data set, as well as the breakdown of animals according

to inbreeding class for all breeds, is summarized in Table 4. Mean inbreeding for each of

the data sets used in the analyses is generally higher than the average level of inbreeding

for each respective purebred population in recent years as reported by Mc Parland et al.

(2007b). This is likely due to the inclusion of only animals with 3 complete generations

of recorded pedigree information in the present study.

Carcass Measures

Mean carcass weight, fat score, and conformation score across breeds, as well as

linear regression solutions for inbreeding effects on these traits, are summarized in Table

5. The Charolais, Hereford, and Angus all showed a linear (P<0.05) reduction in carcass

weight with increased inbreeding, the effects being greater in the British beef breeds.

Solutions from when inbreeding was treated as a class variable were also significantly

different from non-inbred animals in Hereford (P<0.05) and Angus (P<0.01) for animals

up to 6.25% inbred, and in Hereford for animals greater than 12.5% inbred. Class effects

followed the same trend as the linear solutions in all 3 breeds. Inbreeding did not

significantly affect carcass weight in the Limousin or Simmental breeds (Table 5).

Inbreeding only significantly affected carcass fat score in the 2 British breeds,

Angus and Hereford. When treated as either a continuous or class variable, inbreeding

reduced fat score (Table 5). Inbreeding did not significantly affect carcass conformation

score (Table 5) except in Limousin, where the effect of inbreeding differed (P<0.05) by

the gender of the animal. Inbreeding affected conformation score of females (-0.04;




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SE=0.018 score units per 1% increase in inbreeding) more than in either steers (0.03;

SE=0.026 score units per 1% increase in inbreeding) or bulls (-0.01; SE=0.016 score

units per 1% increase in inbreeding).

In summary, the results show that inbreeding within pedigree Irish beef

populations has a minimal effect on the carcass traits investigated. Although regression

coefficients were not always significantly different from zero, with only a few exceptions

the trend was for inbreeding to reduce the level of traits. For example, the effect of

inbreeding on carcass fatness was negative in the British breeds and near zero though

positive in the Continental breeds.

Marshall (1994) reviewed body composition differences in beef cattle and showed

in a pooled across-study sire breed comparison that the Continental breeds of Charolais,

Limousin, and Simmental have greater carcass weight and less fat than the British breeds

of Angus and Hereford. In agreement with Marshall (1994), Continental animals in our

study had heavier, leaner carcasses than British breed animals. Since both carcass weight

and fatness are heritable (Eriksson et al., 2003), these differences may reflect allele

frequency variation at genes governing these traits across breeds. The magnitude of

inbreeding depression is dependent on allele frequency (Falconer and Mackay, 1996),

alleles at intermediate frequencies having a greater effect than alleles at high frequencies.

Alleles at intermediate frequencies may be less inclined to exist in the more highly

selected Continental breeds, which would help to explain the negligible effect of

inbreeding on carcass weight and fat observed in these breeds. Burrow (1998) also

reported decreased carcass weight and fat with increased inbreeding from a study

involving Brahman, Hereford, Shorthorn, and Africander genetics. The inbreeding effects




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reported by Burrow (1998) were also small and were non-significant. However, the

measures of carcass weight and fat used, hot standard carcass weight and fat thickness at

the P8 rump site, were different from the measures in the present study.

There are several possible explanations for both the low level of inbreeding

effects on carcass traits reported in this study and the lack of significant findings. Firstly,

inbreeding may not truly affect carcass traits. Inbreeding depression tends to have a

greater impact on fitness traits such as those associated with reproduction and maternal

traits like milk yield (Falconer and Mackay, 1996). However, high carcass weight would

not be considered necessary for survival of animal or progeny, and thus may not be

largely affected by inbreeding. Secondly, small data sets combined with low average and

variation in inbreeding (Table 4) may affect the potential to accurately and precisely

quantify truly significant results. Thirdly, the low level of inbreeding effects may be due

to intense selection for these traits by breeders and so inbreeding effects may be

confounded with selection (Alexander and Bogart, 1961). This may be particularly

apparent in the case of highly heritable traits (Alexander and Bogart, 1961), although this

should be corrected for within the animal model, which accounts for relationships

between animals and assortative mating. Fourthly, inbreeding effects are expected to be

expressed to a lesser degree in traits controlled primarily by additive genes (Davenport,

1908) such as carcass traits. Fifthly, as these results are representative of commercial

populations, inbreeding effects may be masked by preferential treatment of animals or

delayed slaughtering dates. When age at slaughter was included as a fixed effect in the

model, it was found to have a significant effect on all carcass traits, reducing the F-

statistic for inbreeding effects and resulting in a non-significant effect of inbreeding on




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carcass weight. However, it was removed from the final model as age and inbreeding

were themselves partially confounded. As discussed below, inbreeding significantly

affected age of the animal at slaughter. Including age in the model would thus have

removed part of any inbreeding effect. Finally, Ireland has a mild temperate climate and

it has been suggested in the literature (Keller and Brinks, 1978; Burrow 1998) that

inbreeding effects are expressed to a greater degree in animals reared in dry tropical areas

than in milder climates as exist in Ireland.

Carcass Growth

Mean ADCG and the linear effect of inbreeding on ADCG are presented in Table

5. While both positive (Charolais and Hereford) and negative (Limousin, Simmental, and

Angus) effects were observed (Table 5), the effect of inbreeding on ADCG was

significantly different from zero only in Charolais and only when inbreeding was

examined as a class effect (P<0.01). Inbred Charolais had increased ADCG by 0.02

(SE=0.007) kg, 0.02 (SE=0.014) kg, and 0.007 (SE=0.019) kg for inbreeding classes

0<F≤6.25, 6.25<F≤12.5, and 12.5<F≤25, respectively, and reduced ADCG by -0.08

(SE=0.031) kg for inbreeding class F>25, relative to non-inbred animals. Thus, ADCG

was only reduced in the highly inbred animals, which may explain the lack of

significance of the linear regression effect. Inbreeding has previously been estimated to

have a negative effect (Burrow, 1998) or an effect not significantly different from zero

(MacNeil et al., 1992) on average daily gain from weaning to 12 or 18 months of age.

However, average daily carcass gain from birth to slaughter as calculated in the present




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study is not comparable with results obtained from the previous studies where only gain

during the postweaning period was investigated.

Mean age at slaughter was 759, 758, 736, 772, and 818 (SD=168.7 to 190.3) d for

the Charolais, Limousin, Simmental, Hereford, and Angus, respectively. Inbred Charolais

and Hereford animals were younger at slaughter by 2.58 d (P<0.01) and 4.79 d (P<0.01),

respectively, per percent increase in inbreeding. Also, analysis as a class effect (P<0.001)

showed Charolais animals with inbreeding of 0<F≤6.25 had reduced time to slaughter of

31.07 (SE=8.957) d, whereas animals with inbreeding greater than 25% had a reduced

time to slaughter of 130.00 (SE=39.51) d. The effects of inbreeding appear to be much

greater in the Charolais breed when inbreeding was treated as a class variable (P<0.001)

than when inbreeding was treated as a continuous variable (P<0.01). The linear response

may be upset by the small group of animals in the 12.5<F≤25 class having a non-

significant and variable response. The effect of inbreeding on age at slaughter in

Limousin and Angus animals differed significantly (P<0.05) with animal gender.

Limousin and Angus heifers were significantly younger at slaughter by 4.7 (SE=1.76) d

and 6.9 (SE=3.66) d, respectively, per unit increase in inbreeding. Inbred Limousin steers

and bulls were older at slaughter by 1.4 and 0.8 (SE=2.46 and 1.51) d, respectively, per

percent increase in inbreeding. Corresponding values for Angus steers and bulls were 0.4

and 10.4 (SE=3.09 and 6.01) d, respectively.

Alexander and Bogart (1961) investigated the effect of inbreeding on the age at

which Hereford and Angus cattle reached the target weights of 500 lb and 800 lb (i.e.,

227 kg and 363 kg, respectively) and found male and female inbred animals (analyzed

together) to be significantly older upon reaching these target weights. Our results tend to




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disagree with the findings of Alexander and Bogart (1961) as inbred heifers were

slaughtered at an earlier age than their non-inbred herd contemporaries. However, it is

difficult to compare the results obtained in this study with those obtained by Alexander

and Bogart (1961). Firstly Alexander and Bogart (1961) did not differentiate between the

sexes, and secondly, the study by Alexander and Bogart (1961) was based on closed lines

maintained at an experiment station. In contrast, results from this study were obtained

from animals maintained in commercial and pedigree herds, whereby the farmer or

breeder may operate a selective feeding strategy. This would explain the reduced time to

slaughter of the more inbred animals. Inbred animals are smaller at birth (MacNeil et al.,

1989; Pariacote et al., 1998) and have lower weaning weights (Nelms and Stratton, 1967;

Keller and Brinks, 1978; MacNeil et al., 1989) and mature weights (McCurley et al.,

1984). Therefore, the option of holding inbred animals on farm longer to reach target

weights may not be economically viable to commercial farmers. Instead, these animals

may be removed from the herd at an earlier age, thereby resulting in inbred animals being

younger at slaughter.

Live Measures

The effects of inbreeding on live measures of all 5 breeds are summarized in

Table 6. Inbreeding affected almost all skeletal and muscling traits in Charolais,

Limousin, and Simmental animals, with inbred animals being smaller and narrower in

shape with poorer developed muscle. However, inbreeding did not affect locomotion or

docility in any breed. The effect of inbreeding on skeletal and muscling traits of the

British breeds was generally not significantly different from zero and in some instances




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differed in sign when compared to the Continental breeds. The authors are unaware of

any other studies that quantified inbreeding depression on live conformation measures in

beef cattle such as is provided here, although a reduction in overall conformation score at

weaning with increased inbreeding has been reported (Dinkel et al., 1968), as well as a

negative effect of inbreeding on scrotal circumference (Smith et al., 1989; Burrow, 1998).

In the present study, inbreeding reduced scrotal circumference score in the Hereford

breed only, despite previously reported effects in Angus and Red Angus cattle (Smith et

al., 1989) and tropical beef cattle (Burrow, 1998). However, the impact on scrotal

circumference in Herefords is not consistent in the literature; some previous studies

reported no significant effect in Hereford calves (Anderson et al., 2000), while others

(Smith et al., 1989) reported a reduction in scrotal circumference of -0.03 cm per 1%

increase in inbreeding in yearling Hereford bulls.

It is interesting to note some differences between the results on live measures and

those on carcass measures within this study. Inbreeding effects on carcass weight and

carcass fat score were generally confined to the British breeds, with the Continental

breeds mostly experiencing effects not significantly different from zero. In contrast,

inbreeding effects on the live measures of muscle development and skeletal trait scores

were observed predominantly in the Continental breeds. We propose 3 hypotheses that

may provide an explanation for this difference. Firstly, inbreeding has the greatest effects

on animals early in life (Nelson and Lush, 1950; Davenport et al., 1965), and so, while

inbreeding may be considered a factor in the stunted development of these live measures

in the Continental animals, natural compensatory growth may overcome the inbreeding

depression later on in their development, as the carcass weight of Continentals was




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generally not affected by inbreeding in the present study. As the Hereford and Angus

beef breeds are earlier maturing than the larger Continental Charolais and Limousins

(Martin et al., 1992), compensatory growth may have already recovered the inbreeding

depression in the Angus and Hereford by the time of live scoring. Secondly, the results

may have the same explanation as the lack of significant findings in the carcass analyses.

The smallest animals with underdeveloped muscle at the time of scoring subsequently

may have been preferentially treated in order to have all herd contemporaries at the same

carcass grade by the time of slaughter. These preferentially treated animals would then

not express inbreeding effects at slaughter. And thirdly, differences may exist in allele

frequencies across breeds. As the British beef breeds have not actively been selected for

larger frames or for muscular carcasses, they are likely to have lower allele frequencies

for these traits, and as mentioned previously, it is intermediate allele frequencies that are

most predisposed to inbreeding effects.

Calving Measures

The authors are unaware of any studies that have attempted to quantify inbreeding

effects on calving performance in beef animals, although two studies, Adamec et al.

(2006) and Mc Parland et al. (2007a) have previously reported unfavorable, albeit

biologically small, effects of inbreeding on these traits in US Holsteins and Irish

Holstein-Friesians, respectively.

The incidence of perinatal mortality, dystocia, and twinning in the analyzed data

is detailed in Table 7. A greater number of calf records than dam records were available

for analysis as the calves had more complete pedigree records. The incidence of perinatal




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mortality was greatest in first parity animals at 6.3, 5.6, 4.8, 5.0, and 3.4% for Charolais,

Limousin, Simmental, Hereford, and Angus dams, respectively. These figures are similar

to those of 5.9 and 5.6% reported in first parity Swedish Charolais and Herefords,

respectively (Eriksson et al., 2004). The incidence of dystocia was also greatest in first

parity animals, ranging from 15.5% (Angus) to 41.5% (Charolais). Dam and calf

inbreeding were studied separately as both maternal and fetal effects have previously

been shown to influence stillbirth in dairy cattle (Mc Parland et al., 2007a). Neither dam

nor calf inbreeding affected the rate of twinning in any breed. Mc Parland et al. (2007a)

also failed to find an association between inbreeding and twinning in dairy cattle.

Perinatal Mortality. There was no significant effect of dam inbreeding on

perinatal mortality within the Charolais, Simmental, or Angus breeds. The effect of dam

inbreeding on perinatal mortality differed according to the parity of dam in Limousin

animals (P<0.05), with changes in incidence of 0.66 (SE=0.22%), 0.37 (SE=0.20%), 0.01

(SE=0.21%), 0.13 (SE=0.23%), and -0.13 (SE=0.16%) for parities 1 to 5, respectively.

Hereford dam inbreeding only significantly affected perinatal mortality when included as

a class effect (P<0.05), with increased inbreeding being associated with reduced perinatal

mortality.

Calf inbreeding did not significantly affect perinatal mortality in Limousin or

Angus animals. The effect of calf inbreeding on perinatal mortality differed by dam

parity and calf sex in Charolais and Hereford animals. The effect of Simmental calf

inbreeding on perinatal mortality differed significantly with calf sex (Table 8).

The larger effects of calf inbreeding on perinatal mortality in younger dams

(Table 8) is in semi-agreement with Mc Parland et al. (2007a), who found a greater effect




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of calf inbreeding on stillbirths in primiparous Holstein-Friesian dams. Contrasting

results were obtained from the interaction between inbreeding and sex in its effects on

perinatal mortality among the various breeds. Inbreeding had the greatest effect on male

Charolais calves. However, inbreeding only affected perinatal mortality in Hereford and

Simmental female calves. Inbred calves are smaller at birth (MacNeil et al., 1989;

Pariacote et al., 1998), which potentially predisposes them to a greater probability of

perinatal mortality, as very small calves may have reduced viability (Eriksson et al.,

2004). Koots et al. (1994) reported a positive, albeit non-significant, association between

perinatal mortality and birth weight, suggesting that it is the larger calves that are

stillborn. The association between birth weight and perinatal mortality is likely to be

non-linear with both very large and very small calves being more predisposed to perinatal

mortality.

Dystocia. Calf inbreeding did not affect dystocia incidence in any of the 5 breeds.

Mc Parland et al. (2007a), when looking at similar traits in Holstein-Friesian dairy cows,

also failed to find a significant effect of calf inbreeding on dystocia.

Dam inbreeding did not significantly affect dystocia in Charolais, Limousin,

Simmental, or Hereford animals. Increasing dam inbreeding level was significantly

associated with increased dystocia in first parity Angus dams (P<0.05). Solutions for the

effect of dam inbreeding on dystocia in Angus animals were 0.79 (SE=0.312%), -0.23

(SE=0.338%), -0.08 (SE=0.399%), 1.21 (0.679%), and -0.43 (SE=0.430%) for parities 1

to 5, respectively. Although not significantly different from zero, Charolais dam

inbreeding (P=0.06) exhibited a similar interaction with parity in its effects on dystocia,

with the first parity dams only experiencing unfavorable effects significantly different




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from zero. Adamec et al. (2006) also found inbreeding to have the greatest effect on

dystocia in first parity dams. A potential reason for such an effect may be that inbreeding

delays the onset of maturity (Dinkel et al., 1972), resulting in smaller cows that are

naturally more predisposed to dystocia. In addition, the greater incidence of dystocia in

first parity animals, as reported in this study, allows for greater ability to detect

statistically significant results.

IMPLICATIONS

This study has reported the effects of inbreeding across a range of carcass traits,

live measures, and calving performance traits in the largest purebred beef cattle

populations in Ireland. However, Ireland’s commercial beef sector comprises mainly

crossbred cattle, where the level of inbreeding will be lower than is reported here for

purebred populations. In agreement with Burrow (1993), small regressions coupled with

low levels of inbreeding in commercial herds imply that inbreeding will be of little

concern to beef producers in Ireland.

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Table 1. Description of all traits analyzed Trait DescriptionCarcass Measures1

Weight Cold carcass weight Fat Fat on the outside of the carcass and in the thoracic cavity

Conformation Development of the round, back, and shoulderLive Scores2

Loin development Width, length, and fill of the loin Hindquarter development Roundness and fill of the hindquarter as viewed from the side Width at withers Width of the animal at the highest point, above the front legs Width behind withers Width of the animal behind the withers Width at hips Width between the hip bones Depth of rump Distance between the top and bottom of the rump above the hocks Condition score Overall fleshing of the animal Thickness of bone Expression of canon bone size Length of back Distance between the withers and the hip bone Length of pelvis Distance between the hip bone and the rear of the animal Height at withers Height of the animal at the highest point, above the front legs Locomotion Level of correctness when the animal walks Scrotal circumference Circumference of the scrotum Docility Degree of tameness shown by the animal at inspectionCalving Measures Dystocia Calving difficulty (0 = no assistance, 1 = assistance required)

Perinatal mortality Dead 24 hours after birth (0 = no perinatal mortality, 1 = perinatal mortality) Twinning Birth of two calves per dam parity (0 = no twinning, 1 = twinning occurred)

1DAF (2004)2ICBF (2003)




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Table 2. Measurement scale, as well as the mean values, of live measures (SD in parenthesis) for Charolais, Limousin, Simmental, Hereford, and Angus

Trait1 Score Scale2 Charolais Limousin Simmental Hereford Angus

Muscling 1 15

Loin development Low High 8.3 (1.62) 8.6 (1.36) 8.3 (1.63) 7.9 (1.49) 7.3 (1.88)

Hindquarter development Narrow Wide 8.1 (1.56) 9.0 (1.33) 8.4 (1.53) 7.2 (1.45) 6.6 (1.80)

Width at withers Narrow Wide 8.3 (1.70) 9.0 (1.38) 8.4 (1.66) 8.4 (1.51) 8.3 (1.55)

Width behind withers Narrow Wide 7.6 (1.54) 8.1 (1.35) 7.7 (1.57) 7.4 (1.47) 7.0 (1.54)

1 10

Width at hips Narrow Wide 6.0 (0.92) 6.1 (0.99) 5.9 (0.94) 6.1 (1.08) 5.5 (1.19)

Depth of rump Shallow Deep 6.1 (1.05) 6.0 (1.01) 6.2 (1.00) 6.2 (1.06) 6.1 (1.04)

Condition score Poor Good 5.3 (1.25) 5.3 (1.18) 5.4 (1.33) 5.7 (1.25) 5.4 (1.36)

Skeletal 1 10

Thickness of bone Narrow Thick 6.0 (0.99) 5.2 (1.08) 5.6 (0.98) 5.4 (1.10) 4.4 (1.3)

Length of back Short Long 6.7 (1.04) 6.7 (1.04) 6.7 (1.00) 6.0 (1.35) 5.8 (1.27)

Length of pelvis Short Long 6.2 (0.97) 6.5 (1.05) 6.3 (0.97) 6.2 (1.27) 5.6 (1.25)

Height of withers Small Tall 6.2 (1.30) 5.9 (1.07) 6.0 (1.06) 5.1 (1.29) 5.1 (1.21)

Other 1 10

Locomotion Poor Good 6.5 (1.08) 6.8 (1.04) 6.7 (1.01) 6.7 (0.89) 7.1 (0.97)

Scrotal circumference Small Large 6.2 (1.37) 5.6 (1.33) 6.6 (1.38) 6.6 (1.31) 6.1 (1.33)

Docility Not Docile Docile 7.4 (1.19) 7.1 (1.05) 7.4 (1.16) 7.9 (1.01) 7.3 (1.10)

1Means for all traits are significantly different from zero2ICBF (2003)




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Table 3. Number of records included in the calving performance analyses

Charolais Limousin Simmental Hereford AngusParity Dams1 Calves2 Dams Calves Dams Calves Dams Calves Dams Calves1 12689 11733 9901 9378 1358 1637 3114 2915 4109 38802 11278 12353 7745 8326 986 1675 2642 2897 3367 35763 9597 10846 6306 6781 703 1330 2313 2613 2722 29424 7897 8982 5044 5480 491 1100 2028 2309 2159 24085 20420 23551 13146 13993 1091 3091 5639 6292 5084 5643

1 Data set investigating the effect of dam inbreeding on calving performance2 Data set investigating the effect of calf inbreeding on calving performance




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Table 4. Average inbreeding (F, %) and percentage of animals in each inbreeding class for each data set analyzed

Inbreeding ClassAverage F F = 0 0<F≤6.25 6.25<F≤12.5 12.5<F≤25 F>25

Charolais Carcass Measures 0.73 10.65 86.23 1.77 0.99 0.36 Live Measures 0.56 14.02 84.10 1.26 0.45 0.17 Dams1 0.57 15.77 82.59 1.12 0.40 0.13 Calves2 0.70 10.71 86.60 1.47 0.82 0.40Limousin Carcass Measures 0.88 17.76 78.73 1.27 1.40 0.85 Live Measures 0.56 23.78 74.21 1.19 0.59 0.22 Dams 0.56 29.35 68.51 1.33 0.67 0.14 Calves 0.68 17.06 80.41 1.32 0.81 0.40Simmental Carcass Measures 2.11 8.43 85.08 4.41 1.82 0.26 Live Measures 1.87 10.69 83.68 4.29 1.15 0.19 Dams 1.56 21.82 73.28 3.67 1.06 0.17 Calves 1.98 10.10 83.66 4.44 1.48 0.32Hereford Carcass Measures 2.29 6.00 86.00 5.79 1.58 0.63 Live Measures 2.07 7.67 86.16 5.20 0.73 0.24 Dams 1.57 20.23 74.38 4.21 0.96 0.22 Calves 2.21 6.36 86.90 4.57 1.61 0.56Angus Carcass Measures 1.64 23.67 71.48 3.67 0.83 0.36 Live Measures 1.38 25.10 71.20 2.38 0.92 0.40 Dams 1.48 25.58 71.22 2.59 0.43 0.18 Calves 1.54 19.78 76.57 2.57 0.77 0.31

1 Data set investigating the effect of dam inbreeding on calving performance2 Data set investigating the effect of calf inbreeding on calving performance




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Table 5. Unadjusted trait means (SD in parenthesis), and linear regression solutions (SE in parenthesis) and P-values for the effect of inbreeding on carcass weight (kg), fat score (score units), and conformation score (score units), and average daily carcass gain (ADCG (kg)) in Charolais, Limousin, Simmental, Hereford, and Angus

Charolais Limousin Simmental Hereford AngusCarcass Weight Mean 394 (83.67) 382 (83.79) 378 (78.18) 331 (77.86) 334 (79.50 Linear -0.87 (0.437) -0.85 (0.459) 0.07 (0.787) -1.9 (0.612) -1.8 (0.871) P-value <0.05 0.07 0.92 <0.01 <0.05Carcass fat score Mean 5.8 (2.55) 5.8 (2.45) 6.5 (2.57) 8.9 (2.50) 8.2 (2.64) Linear 0 (0.014) 0.01 (0.015) 0.03 (0.032) -0.06 (0.022) -0.09 (0.031) P-value 0.74 0.35 0.36 <0.01 <0.01Carcass conformation score Mean 9.5 (1.85) 10.0 (1.89) 8.8 (1.90) 7.2 (1.74) 7.2 (1.76) Linear 0.002 (0.011) -0.015 (0.012) 0.000 (0.022) 0.005 (0.017) -0.044 (0.023) P-value 0.82 0.21 1.00 0.78 0.06ADCG Mean 0.55 (0.168) 0.53 (0.160) 0.55 (0.168) 0.44 (0.125) 0.42 (0.106) Linear1 0.05 (0.079) -0.14 (0.084) -0.23 (0.173) 0.02 (0.100) -0.16 (0.122) P-value 0.54 0.09 0.18 0.82 0.181 Linear solutions of ADCG*100




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Table 6. Linear regression solutions1 (score units; SE in parenthesis) for the effect of inbreeding on live measures in Charolais, Limousin, Simmental, Hereford, and Angus

Trait2 Charolais Limousin Simmental Hereford AngusMuscular Loin development -2.3 (0.46)*** -2.3 (0.36)*** -1.1 (0.94) -1.4 ( 1.05) 2.6 (1.78) Hindquarter development -2.0 (0.44)*** -1.5 (0.35)*** -2.9 (0.89) ** 1.3 ( 1.01) 1.7 (1.37) Width at withers -2.7 (0.47)*** -1.6 (0.36)*** -3.4 (0.98)*** -1.5 ( 1.08) -0.3 (1.61) Width behind withers -2.4 (0.44)*** -1.5 (0.35)*** -2.1 (0.94) * -1.3 (-1.30) -0.6 (1.55) Width at hips -1.7 (0.28)*** -1.1 (0.22)*** -1.3 (0.54) * -0.8 ( 0.76) -0.1 (1.24) Depth of rump -1.7 (0.43)*** -0.9 (0.32) ** -1.4 (0.72) * -1.2 ( 0.82) 1.2 (1.22) Condition score -0.8 (0.57) -0.8 (0.37) * -1.3 (0.88) 0.0 ( 1.01) 4.8 (1.75) **Skeletal Length of bone -1.6 (0.29)*** -0.4 (0.17) * -0.9 (0.53) -0.5 ( 0.77) 0.7 (1.14) Length of back -1.2 (0.30)*** -1.4 (0.23)*** -1.3 (0.60) * -1.3 ( 0.94) 1.3 (1.20) Length of pelvis -1.4 (0.30)*** -0.7 (0.22) ** -1.4 (0.56) * 0.0 ( 0.95) 2.9 (1.23) * Height at withers -1.9 (0.37)*** -1.5 (0.25)*** -1.2 (0.61) * -0.5 ( 0.88) 1.1 (1.25)Other Locomotion -0.7 (0.53) -0.5 (0.37) -1.0 (0.87) 1.3 ( 1.67) -0.9 (1.14) Scrotal circumference -1.2 (0.85) -0.9 (0.57) -1.6 (1.40) -2.8 ( 1.16) * -0.3 (2.02)

Docility 0.0 (0.54) -0.1 (0.29) -0.2 (1.10) -0.7 ( 0.94) 0.7 (1.62)1 Significance levels for linear solutions denoted by * (P<0.05), ** (P<0.01), *** (P<0.001) 2ICBF (2003)




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Table 7. Incidence of perinatal mortality (%), dystocia1 (%), and twinning (%)Perinatal mortality Dystocia TwinningDams2 Calves3 Dams Calves Dams Calves

Charolais 2.99 1.89 27.58 27.52 6.56 7.32Limousin 3.00 2.14 12.81 12.71 2.15 2.25Simmental 3.04 1.72 16.41 16.61 6.66 8.60Hereford 2.23 1.49 17.22 17.51 4.33 4.27Angus 1.82 1.16 9.17 8.94 3.47 3.53

1 Dystocia was analyzed as a binary variable (0 for unassisted calving, 1 for assisted calving)2 Data set investigating the effect of dam inbreeding on calving performance3 Data set investigating the effect of calf inbreeding on calving performance




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Table 8. Linear regression solutions (*1000; SE in parenthesis) for the effect of calf inbreeding1 on perinatal mortality (%) across different parities and sexes for Charolais and Hereford, and the solution by sex for Simmental

Charolais Simmental2 HerefordP<0.001 P=0.01 P=0.001

Parity Male Female Male Female Male Female1 10.9 (1.24)*** 0.7 (1.21) -0.83 (1.214) 4.46 (1.769)** -1.8 (1.73) 6.3 (1.58)***2 3.5 (1.25) ** 0.9 (1.43) 0.1 (1.61) 4.5 (2.40)3 0.5 (1.31) -3.1 (1.66) -1.9 (1.65) 1.9 (2.23)4 1.1 (1.40) -0.8 (2.32) -1.1 (1.73) 0.2 (2.62)5 -0.4 (1.12) 0.1 (1.29) 0.8 (1.37) -0.6 (2.04)

1Within-group regression coefficients significantly different from zero are denoted by * (P<0.05), ** (P<0.01), *** (P<0.001)2Solutions for Simmental are representative of all dam parities




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