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Influence of Biostimulation by Mature Bulls on Occurrence of Puberty in Beef Heifers^1,2,

Montana State University, Bozeman 59717

Abstract

The objective of this study was to determine if biostimulation of prepuberal beef heifers by mature bulls would alter proportions of heifers exhibiting puberty, or age or weight at puberty. Angus (A), AxHereford (H) and TarentaisexHA heifers (n = 103) were stratified by age and weight within breed-type and location of birth and allotted randomly to the following treatments: 1) heifers exposed to mature bulls (T1; n = 52) or 2) heifers isolated from bulls (T2; n = 51). At the start of the experiment, heifers in T1 and T2 were 287 ± 2 and 286 ± 2 d of age, respectively. Male-to-female ratio for T1 was 1:26. Heifers in T1 and T2 were maintained in drylots separated by .5 km. Heifers were observed for estrus twice daily for 152 d. Puberty was characterized by the following criteria: 1) behavioral estrus, 2) presence of a palpable corpus luteum (d 9; estrus = d 0) and 3) a rise in serum progesterone above 1 ng/ml (d 9). Proportions of heifers reaching puberty by 11, 12, 13, 14 and 15 mo of age did not differ (P>.10) between treatments. Percentages of heifers reaching puberty by the end of the experiment were 84 and 89% for T1 and T2, respectively. Age and weight at puberty did not differ (P>.10) between treatments and averaged 370 ± 7 d and 293 ± 4 kg, respectively. Results from this experiment indicated that presence of mature bulls did not alter proportions of beef heifers reaching puberty, or age and weight at puberty.

¹ Published with the approval of the Director of the Montana Agr. Exp. Sta. as Journal Series No. 1869. The authors gratefully acknowledge that this research was supported in part by a grant from the Natl. Assoc. of Animal Breeders, Coordinated Research Program, Columbia, MO 65205.

² This study was a contribution to the Western Region Project, W112 and was presented in part at the 1985 Annu. Meet. of the West. Sec. of the Amer. Soc. of Anim. Sci.

³ Present address: Dept. of Anim. Sci., Univ. of Nebraska, Lincoln, NE 68583.

⁴ Address rerpint requests to James G. Berardinelli, Dept. of Anim. and Range Sci., 119 Linfield Hall, Montana State Univ., Bozeman, MT 59717.

⁵ Present address: Amer. Simmental Assoc., 1 Simmental Way, Bozeman, MT 59715.