@article{milagres_dillard_robison_1979, title={HERITABILITY ESTIMATES FOR SOME MEASURES OF REPRODUCTION IN HEREFORD HEIFERS}, volume={49}, ISSN={["0021-8812"]}, DOI={10.2527/jas1979.493668x}, abstractNote={Records on 491 Hereford cows were analyzed to estimate heritabilities of some measures of reproduction in the first calving. Estimates were obtained from paternal half-sibs by both analysis of variance (ANOVA) and chi-square (X2)- Heritabilities estimated from ANOVA and from X2 for binary variables were corrected to a normal basis (ANOVA—C and X2 —C). For calving rate at 2 years of age the heritabilities were .01 ± .02 (ANOVA), .02 ± .04 (ANOVA-C), .13 ± .09 (X2) and .22 ± .12 (X2—C). When heifers that failed to calve at both 2 and 3 years of age (barren) were excluded from the data, estimated heritabilities were .21 ± .13 (ANOVA), .45 ± .19 (ANOVA-C), .22 ± .14 (X2) and .48 ± .20 (X2 —C). The heritability of barrenness was .0 ± .04 (ANOVA), .16 + .10 (X2) and .33 ± .15 (X2 —C). Analysis of perinatal survival evaluated as a characteristic of the dam yielded heritability estimates of .64 ± .21 (ANOVA), 1.25 ± .35 (ANOVA—C), .61 + .25 (X2) and 1.19 ± .34 (X2 —C). Heritability of services per conception for the first calving was estimated at .64 ± .29.}, number={3}, journal={JOURNAL OF ANIMAL SCIENCE}, author={MILAGRES, JC and DILLARD, EU and ROBISON, OW}, year={1979}, pages={668–674} }
@article{milagres_dillard_robison_1979, title={INFLUENCES OF AGE AND EARLY GROWTH ON REPRODUCTIVE-PERFORMANCE OF YEARLING HEREFORD HEIFERS}, volume={48}, ISSN={["0021-8812"]}, DOI={10.2527/jas1979.4851089x}, abstractNote={Reproductive performance of 477 Hereford cows entering the breeding herd as yearlings was studied. Variables considered were herd, year, age of dam, birth weight, weaning weight, yearling weight, weight at the beginning of the breeding season, weight at conception and weight at calving of the heifer, age of the heifer at the beginning of the breeding season, age in days at conception and weight of the calf born to the 2-year-old heifer. Age of the heifer at the beginning of the breeding season had a significant quadratic effect (P<.01) on calving rate at 2 years of age. Calving rate increased at a diminishing rate as heifers advanced from 303 to 438 days of age. Of the body weights analyzed, yearling weight had the most important effect (P<.01) on early calving. Only 19% of the variation in calving rate could be accounted for by all 11 variables included in the model. Calf survival in the first calving was quadratically affected (P<.01) by age of the heifer at conception. Heavier yearlings had a lower proportion (P<.01) of dead calves in the first calving. In contrast, weaning weight of the heifer was negatively associated (P<.01) with calf livability in the first calving. Mortality increased with birth weight of the calf (P<.01). Heavier calves had a high probability of failing to survive. A full model containing 18 variables explained about 25% of the variation in perinatal calf mortality. The number of services per conception was not affected by any of the body weights studied nor by age at the start of the breeding season. In this study 67% of the heifers inseminateed calved at 2 years of age, but only 85% of those calving gave birth to calves that were alive at 24 hours.}, number={5}, journal={JOURNAL OF ANIMAL SCIENCE}, author={MILAGRES, JC and DILLARD, EU and ROBISON, OW}, year={1979}, pages={1089–1095} }