HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Milagres, J. C. Articles by Robison, O. W. Search for Related Content PubMed Articles by Milagres, J. C. Articles by Robison, O. W.

Influences of Age and Early Growth on Reproductive Performance of Yearling Hereford Heifers^1,2,3,

North Carolina State University, Raleigh 27650

Abstract

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.

¹ Paper No. 5638 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh.

² The authors express their appreciation to the personnel of the Research Stations at Plymouth and Raleigh for their assistance in collecting the data.

³ Conducted in cooperation with the Southern Regional Project S-10. The Improvement of Beef Cattle for the Southern Region through Breeding Methods.

⁴ Present address: Universidade Federal de Vicosa, 36.570 - Vicosa - MG - Brasil.

⁵ Department of Animal Science.