PHENOTYPIC AND GENETIC PARAMETER ESTIMATES FOR GESTATION LENGTH, CALVING EASE AND BIRTH WEIGHT IN SIMMENTAL CATTLE

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1 NOTES PHENOTYPIC AND GENETIC PARAMETER ESTIMATES FOR GESTATION LENGTH, CALVING EASE AND BIRTH WEIGHT IN SIMMENTAL CATTLE Variance components, heritabilit:ies and genetic and phenotypic correlations were estimated using progeny records of 73 sires on the Young Sire Proving Program (YSPP) of the Canadian Simmental Association. The YSPP was based on random mating of 58 test and 15 reference sires to cows in cooperating herds. Data were collected on several traits but the ones of interest in this study were gestation length (GL), calving ease (CE) and birth weight (BW). Variance and covariance components were estimated using Henderson's method 3. Heritability estimates were0.24,0.06 and 0.19 for GL, CE and BW, respectively. Genetic and phenotypic correlations were negative between GL and CE and CE and BW. Correlations between GL and BW were moderate and positive. Selection programs, utilizing large numbers of progeny per sire, would be effective but should incorporate the correlations between these traits. Key words: Heritabilities, genetic and phenotypic correlations, selection IParamdtres phdnotypiques et g6n6tiques estimatifs de la dur6e de la gestation, de la facilit6 de vdlage et du poids d la naissance chez les bovins Simmental.l Titre abr6g6: Parambtres estimatifs chez les bovins Simmental. Nous avons calcul6 les valeurs estimatives des composantes de la variance, de 1'h6ritabi- 1it6 et des corr6lations g6n6tiques et phdnotypiques )r partir des donn6es des tests sur descendance de 73 taureaux inscrits au Programme d'6preuve des jeunes g6niteurs (YSPP) de l'association canadienne Simmental. Le Programme YSPP 6tait fond6 sur I'accouplement au hasard de 58 taureaux d'6preuve et de 15 taureaux t6moins aux vaches des troupeaux parlicipants. Plusieurs caract6ristiques ont 6t6 6tudi6es mais celles qui nous int6ressaient dans la pr6sente 6tude 6taient la dur6e de la p6riode de gestation (GL), la facilit6 de velage (ce) et le poids d la naissance (Bw). Les composantes de Ia variance et de la covariance ont 6td calcul6es d I'aide de la m6thode 3 de Henderson. Les valeurs estimatives de l'h6ritabilit6 6taient de0,24,0,06 et 0,19 pour GL' CE et BW respectivement. Les corr6lations g6n6tiques et ph6notypiques entre GL et CE et entre CE et BW 6taient n6gatives. Les corr6lations entre GL et BW 6taient mod6r6es et positives. Les programmes de s6lection utilisant un grand nombre de descendants par taureau peuvent 6tre efficace mais ils devraient incorporer les corr6lations entre ces caract6ristiques. Mots cl6s: H6ritabilit6, correlations g6n6tiques et ph6notypiques' s6lection Expected Progeny Differences (EPD) are parameters is especially lacking for reproducrequired for genetic improvement programs tion and birth traits. The objective of this ru.h as young sire provlng programs. These study was to estimate phenotypic and genetic predicted values aie usually obtained from parameters of direct (sire) traits from the best linear unbiased prediction procedures Canadian Simmental Association Young Sire using mixed model equations (Henderson Proving Program (YSPP). 1963J. Variance components for random and Records from 4345 progeny of 15 reference residual effects are needed to obtain predic- sires and 58 young test sires during 1978 to tions of random effects from mixed linear 1982 were obtained from the YSPP. The models. However, estimates of the variance YSPP was an organized testing program components are used because true population administered by the Canadian Simmental parameters are never known. Knowledge of Association. Semen from test sires was can. J. Anim. sci.6e: zst-2s..mar. 1e88) *:Ti"i*#x:"T:;ffiJl;;:':; Ji"":: 291

2 292 CANADIAN JOURNAL OF ANIMAL SCIENCE participation although a testing charge was levied against owners of the test sires. Reference sires were chosen by the test administrator based on weaning weight EPD, semen cost and availability and breeder acceptability. Semen was distributed to the cooperating herds by the test administrator with each herd using at least two test sires and one reference sire each year. Each cooperator agreed to use the semen randomly across the cow herd and to raise all calves under similar management conditions. Cooperators measured several variables but for the purposes of this study data were used on gestation length (GL), calving ease (CE) and birth weight (BW). The mean values for birth weight and gestation length were 39.6 kg and d, respectively. Calving ease was reported as unassisted, easy pull, hard pull or surgical and converted to numerical scores of 100, 50, 30 and 0, respectively (Tong et a. 1977). Forty-eight percent of the first calf heifers and 82% of the mature cows were classed as unassisted births. Data were classified into five breed of dam groups (50% Simmental,15% or greater Simmental, 50% or 15% British breeds, 100% British breeds or miscellaneous). In cases where dams could be classified into two groups (e.g. 50% Simmental or 50% British) the group choice was based on breed of sire of the dam. Four age of dam groups ( < 31, 3l-42, arrd >54 mo) were used in classifying the data. The sex ofeach calfand the herd-year in which it was born and raised were also recorded. For more detail on breed of dam, age of dam, sex of calf effects and distribution of records within these subclasses see Kemp et al. (1984). Matings were randomized over all age of dam and breed of dam groups. Pedigree information was supplied for each of the 73 sires used in the program. The mixed linear model used for variance component estimation was y:xh*wm1-zs*e where y was a vector of GL, CE, or BW, h was a vector of fixed herd-year effects, m was a vector of hxed breed of dam by age of dam by sex of calf subclass effects, s was a vector of random sire effects and e was a vector of random residual effects. Seasonal effects were assumed to be eliminated by the h effects because calvings in any herd year combination were within a short time period. The X, W and Z were known incidence matrices of zeros and ones. Expectations were E v s e Xh*Wm wrth variance-covariance matrix random effects 0 0 Ao.t 0 lo.t of the where A represents the numerator relationship matrix due to sires and maternal grandsires and I was an identity matrix of appropriate order. Variance components were estimated using Henderson's Method 3 (Henderson 1953) and heritabilities were calculated using paternal half-sib analysis. Standard quadratic forms of Henderson's Method 3 were adjusted to include the relationship matrix. Estimates were also computed using Henderson's new method (Method 4), MIVQUE, REML and ML with the same model. These resulted in essentially identical estimates for all parameters with each method. Therefore, estimates from Henderson's Method 3 are presented because of the general familiarity of readers with this method and the absence of any selection occurring in the dataset since it was from an organized and well-controlled young sire proving program. Covariance components were estimated by using the summed traits method as follows, o,,r:0.5(o?,*rr-4-q, where o21^+r; refers to the variance compo-

3 KEMP ET AL, PARAMETER ESTIMATES IN SIMMENTAL CATTLE 293 Table l Heritabilities, genetic and phenotypic correlation estimatesti Trait Gestation length Calving ease Birth Weight Gestation Calving Birth length ease weight o testimated using Henderson's Method 3. {Heritabilities on diagonal, genetic correlations above and phenotypic correlations below diagonal. nent that results from summing traits x and y. Sire variance estimates were 2.5 &, 4.1 pts2 and 1.1 kg2 for GL, CE and BW, respectively. Phenotypic variance estimates for GL, CE and BW were 413 d2, pts2 and 23.3 kgz, respectively. Sire variance estimates for GL were similar to estimates reported by Wray et al. (1986) and Azzam and Nielsen (1987) but larger than estimates by Burfening et al. (1981). The heritability estimate (Table l) for GL was similar to the estimate reported by Burfening et al. (1981) but smaller than estimates of Bourdon and Brinks (1982), Wray et al. (1986) and Azzam and Nielsen (1987). Heritability estimates for CE from Schaeffer and Wilton (1981), for male calves, Burfening et al. (1981) and unpublished reports from the Simmental Sire Selector (1987) agreed closely with the estimate from this study. Bourdon and Brinks (1982) reported a larger BW heritability estimate than was determined from this study which was similar to the estimates from Burfening et al. (1981) and the Simmental Sire Selector (1987). The CE scoring system must be remembered when interpreting the correlations (Table 1) involving this trait. The moderate negative genetic and small negative phenotypic correlations between GL and CE agree closely with the estimates of Burfening et al. (1981). These correlations suggest that as GL increases, the probability ofa difhcult calving also increases but there appears to be a large environmental effect. The moderate positive genetic correlation between GL and BW is in general agreement with estimates from other studies. However, Burfening et al. (1981) reported a larger value and Bourdon and Brinks (1982) estimated a slightly smaller genetic correlation than was found in this study. The low positive phenotypic correlation between GL and BW was similar to estimates by Burfening et al. (198 1) and Bourdon and Brinks (1982). These correlations suggest that selection for a shorter gestation length would result in lower birth weights and lessdiff,rcult calvings. However, one would expect that responses to this type of selection may be small due to opposing natural tendencies of gestation time and perhaps a minimum birth weight under which survival could become an overriding factor. The large negative genetic and moderate negative phenotypic correlations between CE and BW were very similar to values reported by Burfening et al. (1981) and Schaeffer and Wilton (1981). The actual genetic correlation was outside the acceptable range but supported the strong relationship between the two traits previously reported. These results imply that selection for lighter birth weights would reduce calving difficulty, but again environmental influences do exist. Variance components specihc to every dataset and analysis model should be estimated for use in obtaining solutions. The parameter estimates presented in this paper would give an indication of the magnitude and relationships between the traits for most datasets. Since the estimates are outside the parameter space and the variance covariance matrices are not positive defrnite, their use in models for other datasets is questionable. The results of this study indicate that selection programs for CE, GL and BW could be effective but large numbers of progeny per sire would be required for accurate genetic evaluations. As well, since calving ease.would probably be the trait of most interest, and because it has low heritability, its improvement through selection should consider the correlated influences of gestation length and birth weight using multiple trait models. Selection and evaluation programs that do not account for these effects may result in selec-

4 294 CANADIAN JOURNAL OF ANIMAL SCIENCE tion of below average animals with lowered response to selection. The authors are grateful to the Canadian Simmental Association for supplying the data and the Natural Sciences and Engineering Research Council of Canada for financial assistance. Azzam, S. M. and Nielsen, M. K Generic parameters for gestation length, birth date and frrst breeding date in beef cattle. J. Anim. Sci. 64: 348. Bourdon, R. M. and Brinks, J. S Genetic, environmental and phenotypic relationships among gestation length, birth weight, growth traits and age at first calving in beef cattle. J. Anim. Sci. 55: 543. Burfening, P. J,, Kress, D. D., Friedrich, R. L. and Vaniman, D. D Phenotypic and genetic relationships between calving ease, gestation length, birth weight and preweaning growth. J. Anim. Sci. 47: 595. Burfening, P. J., Kress, D. D, and Friedrich, R. L Calving ease and growth rate of Simmental-sired calves. III. Direct and maternal effects. J. Anim. Sci. 53: Henderson, C. R Estimation of variance and covariance components. Biometrics 9: 226. Henderson, C. R Selection index and expected genetic advance. Pages 14l-163 in Statistical genetics and plant breeding. National Academy of Science-National Research Council, Washington, D. C. Publ Kemp, R. A., Schaeffer, L. R. and Wilton, J. W Comparison of beef sire evaluation models for an organized progeny test. J. Anim. Sci. 58:1313. Schaeffer, L. R. and Wilton, J. W Comparison of single and multiple trait beef sire evaluations. Can. J. Anim. Sci. 61: 565. Simmental Sire Selector American Simmental Association, Bozeman, Mont. Tong, A. K. W., Wilton, J. W. and Schaeffer, L. R Application of a scoring procedure and transformation to dairy type classifications and beef ease of calving categorical data. Can. J. Anim. Sci.57: 1. Wray, N. R., Quass, R. L. and Pollak, E. J Direct and maternal additive genetic variance components of gestation length in Simmental cattle. J. Anim. Sci. 63 (Suppl. l): 197. R. A. KEMPI, J. W. WILTON, and L. R. SCHAEFFER Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada NIG 2W1. Received 27 July accedted 26 Oct rpresent address (R.A.K.): Department of Meat and Animal Science, 1675 Observatory Drive, University of Wisconsin-Madison, Madison, WI 53706, U.S.A.

5 This article has been cited by: 1. J. Jamrozik, S.P. Miller Genetic evaluation of calving ease in Canadian Simmentals using birth weight and gestation length as correlated traits. Livestock Science 162, [CrossRef] 2. P. R. Amer, R. Crump, G. Simm A terminal sire selection index for UK beef cattle. Animal Science 67, [CrossRef]