Genetic, Environmental and Phenotypic Relationships among Gestation Length, Birth Weight, Growth Traits and Age at First Calving in Beef Cattle

Abstract

Data on the Red Angus, Angus and Hereford herds of Pioneer Hi-Bred International, Inc., Des Moines, Iowa, collected from 1968 to 1976, were analyzed for relationships among gestation length, birth weight, prenatal gain (birth weight adjusted for gestation length), growth traits and age at first calving. A total of 5,691 calf records, 1,783 listing gestation length, were included in the study. Paternal half-sib analyses and least-squares procedures were used to compute heritability estimates and genetic, environmental and phenotypic correlations among traits. Genetic correlations among growth traits, including prenatal gain, were high in all cases. Heritability estimates for gestation length and birth weight were .36 and .43, respectively, for bull calves and .37 and .35 for heifer calves. Genetic correlations between these traits were .25 and .22 for bull and heifer calves, respectively. Gestation length was negatively correlated (genetically) with all growth traits except birth weight. This result suggests that faster growing fetuses may trigger parturition earlier than average. Age at first calving was negatively correlated (genetically) with growth traits, indicating a favorable relationship between growth and early reproduction. Analysis of several selection indexes combining either birth weight and yearling weight or gestation length and yearling weight indicated that continued response to selection for growth without excessive increase in birth weight is feasible. Selection for growth and moderate birth weight would be more effective than selection for growth and shorter gestation, suggesting that the former method would both shorten gestation and alter the growth curve. Repeatability estimates for gestation length and birth weight were .20 and .22, respectively. Maternal effects accounted for approximately 10% of the variation in each trait.

Direct genetic and maternal variance and covariance component estimates from Angus and Hereford field data

“…The estimates reported by Everett and Magee (1965), Burfening et al (1981), and Bourdon and Brinks (1982) generally concur with Koch's averages but still show variety. Brown and Galvez (1969) disagreed slightly from Vesely and Robison (1971) report variances for direct effect that were higher than most others reviewed.…”

“…From the values in Table 1, the conclusion is drawn that relatively higher proportion of direct than maternal variance exists for birth weight, agreeing with general conclusions of Bourdon and Brinks (1982). They concluded that direct effects for birth weight account for three to four times more variation than do maternal effects.…”

“…Bourdon and Brinks (1982) decided to assume r. .. = 0 because of lack of literature A'M evidence to the contrary. These results would concur with conclusions ffom this study.…”

“…Both researchers nonetheless indicated that the correlations should be treated as rough estimates due to the approximate nature of the method. Bourdon and Brinks (1982) even made the assumption that the covariance of direct and maternal birth weight was zero because of the absence of convincing evidence to the contrary.…”

Análise genética de algumas características reprodutivas e suas relações com o desempenho ponderal na raça Nelore

“…Vários trabalhos relatam correlação positiva entre DG e PESNAS (Lôbo et al, 2000), indicando que a duração de gestação mais longa está associada a maior peso ao nascer, conseqüentemente maior DG estaria ligada à maior dificuldade de parto (McGuirk et al, 1999). São poucos os resultados encontrados sobre correlação entre DG e outras características de desempenho ponderal, mas alguns deles diferem do que foi obtido no presente estudo, ao apresentarem correlação negativa entre DG e peso à desmama, peso a um ano, ganhos de peso do nascimento à desmama, da desmama a um ano e na pós-desmama (Bourdon & Brinks, 1982). Pelos resultados obtidos pode-se supor que a seleção para PESDES, PESSOB e GP345 resultaria em aumento da DG e do PESNAS.…”