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Induced or Synchronized Puberty in Heifers¹

U. S. Department of Agriculture and Montana Agricultural Experiment Station, Miles City 59301

Abstract

Three experiments were conducted to examine different hormone treatments for their effectiveness in inducing or synchronizing a fertile estrus in prepuberal heifers. In experiments I and II, heifers which averaged 8.5 months of age and 249 kg in weight were given treatment E (5 mg E₂ß, experiment I), treatment PE (silastic rubber implant containing 2.1 g progesterone for 6 days and an injection of 5 mg E₂ß 24 hr after implant removal, experiments I and II) or treatment S-6 (6 mg SC-21009 progestogen implant for 6 days with an injection of 3 mg SC-21009 and 5 mg estradiol valerate at the time of implanting, experiment II). In experiment I, treatment PE increased the number of heifers showing estrus within 4 days (P<.01) and ovulating (P<.05). However, no significant differences in pregnancy rate were found after 4 or 45 days of breeding. In experiment II, more PE treated heifers than S-6 treated heifers were in estrus after 4 days (P<.01) but pregnancy rates were low and differences were small after 4 (P>.25) or 45 (P<12) days of breeding. In experiment III, heifers which averaged 13.7 months of age and 323 kg in weight were divided into puberal and prepuberal. The prepuberal heifers were given treatment S-9 (same as S-6 except implant period was 9 days) or SE (SC-21009 implant for 9 days with an injection of 5 mg E₂ß 24 hr after implant removal). Detection rate of the first estrus (after 4 days in prepuberal vs 22 days in puberal) was similar (P>.5) in all groups. Pregnancy rates were lower in SE heifers at the first estrus (P<.01) and after 45 days of breeding (P<.05). These data indicate that a fertile estrus can be hormonally induced or synchronized in prepuberal heifers of normal age (13 to 15 months) and to a lesser degree in very young heifers (<9 months).

¹ This study was a contribution to Western Regional Research Project W-112, Reproductive Performance in Beef Cattle. Publication has been approved by the Director of the Montana Agricultural Experiment Station, Journal Series No. 600.

² U. S. Range Livestock Experiment Station, U.S.D.A.-A.R.S., Miles City, MT 59301.

³ Montana Agricultural Experiment Station, Miles City, MT 59301.

⁴ Present address: East Texas Research and Extension Center, Drawer E, Overton, TX 75684.

⁵ Authors express appreciation to: G. D. Searle Co., Chicago, IL, for SC-21009 implants; Dr. G. D. Niswender, Colorado State University, for anti-bovine LH serum; Dr. L. E. Reichert, Jr., Emory University for purified bovine LH; Wayne Graves, Morris Krausz, Paul Ledbetter and Miss Ann Darling for technical assistance.

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