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Synchronization of Estrus in Gilts with Allyl Trenbolone: Fecundity after Natural Service and Insemination with Frozen Semen^1,2,

US Department of Agriculture^,6, Beltsville, MD 20705; Miles City, MT 59301 and Montana State University, Bozeman 59717

Abstract

The synthetic progestogen, allyl trenbolone, was fed daily to 60 gilts at 15 mg/gilt for 18 days. Sixty-eight gilts that came into estrus the same week as treated gilts served as controls. Gilts were checked for estrus twice daily and were artificially inseminated with frozen semen or bred by natural service. All but two treated gilts returned to estrus between 4 and 7 days after withdrawal of allyl trenbolone (mean = 5.6; SD = .82). The farrowing rate among gilts inseminated with frozen semen was significantly lower than that among gilts bred by natural service (52.5 vs 89.6%). The farrowing rate among synchronized gilts was similar to that among untreated gilts (70.7 vs 73.5%). Average total and live litter sizes at birth and litter size at weaning were significantly smaller for untreated gilts inseminated with frozen semen than for synchronized gilts inseminated with frozen semen or those of untreated gilts bred by natural service. Average litter size for synchronized gilts bred by natural service was not significantly larger than that for synchronized gilts inseminated with frozen semen or that of untreated gilts bred by natural service.

¹ Publication has been approved by the Director of the Montana Agr. Exp. Sta., Journal Ser. No. 1058.

² We thank Dr. S. K. Webel, Reproductive Consulting Service, McHenry, IL, and The Roussel Uclaf Company, Paris, France, for supplying allyl trenbolone, and Dr. Caird E. Rexroad, Jr. for statistical analyses.

³ SEA, AR, Beltsville Agricultural Research Center, Reprod. Lab.

⁴ Livestock and Range Res. Sta., Miles City, MT.

⁵ Dept. of Anim. and Range Sci., Montana State Univ., Bozeman.

⁶ Mention of a trade name, proprietary product or vendor does not constitute a guarantee or warranty by the USDA and does not imply its approval to the exclusion of other products or vendors that may also be suitable.