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Heterosis among Closed Lines of Hereford Cattle II. Postweaning Growth and Puberty in Heifers¹

Montana State University, Bozeman 59717

Abstract

Reciprocal crosses among five closed lines of Hereford cattle were made over a 3-year period. After weaning (initial weight), all heifer calves were fed as a group to gain approximately .6 kg/day and a final weight was taken after a 168-day postweaning period (final weight). Sterilized bulls were placed with the heifers to check for estrus beginning after January 1 when the heifers were approximately 10 months of age. Weight at first estrus was estimated from the 28-day weights nearest estrus. Line of sire significantly affected postweaning average daily gain (ADG) and final weight; line of dam significantly affected initial weight, postweaning ADG and final weight. Line of sire by line of dam affected (P<.05) final weight. Heterosis estimates were 11 kg (6%), .06 kg/day (11%) and 20 kg (7%) for initial weight, postweaning ADG and final weight, respectively. Line of sire significantly affected weight at first estrus and the percentage cycling at 12 and 13 months of age. Line of dam significantly affected age at first estrus, weight at first estrus and percentage cycling at 14 months of age. Line of sire by line of dam was not significant for the puberty traits. Heterosis estimates for the puberty traits were -11 days (–3%), 14 kg (5%), 5% (20%), 8% (16%) and -1 (–1%) for age at first estrus, weight at first estrus and the percentage cycling at 12, 13 and 14 months of age, respectively. Genetic correlations between transmitted and maternal effects were -.85 for initial weight, -.75 for final weight, -.87 for postweaning ADG, -.28 for age at first estrus, -.77 for weight at first estrus and -.98, -.66 and .25 for percentage cycling at 12, 13 and 14 months of age, respectively.

¹ Published with approval of the Director of the Montana Agricultural Experiment Station, Journal Series No. 893.

² Northern Agricultural Research Center, Havre, MT 59501.