Prepuberal Behavior and Puberal Characteristics of Beef Bulls on High Nutrient Allowance

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Abstract
Twelve Angus and 15 Hereford weanling pure bred bulls were used to study prepuberal sexual behavior and physical and seminal characteristics at puberty. Only 20 of the 27 calves contributed information on characteristics at puberty; 4 were discarded for deficiencies affecting reproduction and 3 for reasons unrelated to reproduction. For the 20 bulls the average age in weeks for collection with artificial vagina of the 1st sperm, of the 1st motile sperm and of the 1st ejaculate meeting puberal criteria (minimum of 10% progressively motile sperm and 50 x 106 sperm) was 41 [plus or minus] 1, 43 [plus or minus] 1, and 45 [plus or minus] 1, respectively. Body weight at puberty averaged 697 [plus or minus] 24 lb.; the ranges in age and body weight were 39 to 52 weeks and 472 to 898 lb. Semen characteristics and freezability of the 1st ejaculate were highly variable. First ejaculates for 5 bulls, however, satisfactorily withstood freezing and 3 weeks of storage in liquid nitrogen. Prior to puberty, 20 of the 27 calves mounted at the rear of the stimulus animal more than 85% of the time. In general, there was no improvement in mounting orientation with mounting experience. The age at which the 1st motile sperm were obtained using the artificial vagina compared favorably with that reported using electroejaculation. No significant breed differences were observed.

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