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Pennsylvania State University, University Park
Abstract
Twelve Angus and 15 Hereford weanling purebred bulls, fed individually according to recommended nutrient allowances for fattening calves finished as short yearlings, were used to study prepuberal behavior and puberal characteristics. Only 20 of the 27 calves contributed information on characteristics at puberty; four were discarded for deficiencies affecting reproduction and three for reasons unrelated to reproduction. After puberty three bulls were removed from the experiment for reproductive defects.
No significant breed differences were observed in any characteristics studied. For the 20 bulls the average age in weeks for collection with artificial vagina of the first sperm, of the first motile sperm and of the first ejaculate meeting the minimum puberal criteria was 41±1, 43±1, and 45±1, respectively. Body weight at puberty averaged 697±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 first ejaculate were highly variable. First ejaculates for five of the 19 bulls tested, however, satisfactorily withstood freezing and 3 weeks of storage in liquid nitrogen.
Prior to puberty the majority of the 27 calves showed good mounting orientation during a series of weekly, 1-hr., group observations; 20 of the 27 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. Age at first mounting with protrusion in the exercise lot was of no value in predicting age at puberty.
The age at which the first motile sperm were obtained using the artificial vagina compared favorably with that reported using electroejaculation.
1 Authorized for publication as paper No. 2961 in the journal series of The Pennsylvania Agricultural Experiment Station.
2 Departments of Dairy and Poultry Science.
3 The assistance of P. J. Phillips, Jr., Department of Animal Industry and Nutrition, in procurement of the calves is gratefully acknowledged.
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