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Reproductive Performance of Suffolk and Suffolk-Cross Ewes and Ewe Lambs Exposed to Vasectomized Rams before Breeding¹

Purdue University^,4, West Lafayette, IN 47907

Abstract

Multiparous Suffolk and Suffolk-cross ewes were randomly allotted to treatments within breed and year to measure effects of ram exposure, during transition from anestrus to breeding activity, on reproductive performance. Treatments were: 1) ewes joined with two mature vasectomized Rambouillet rams for 15 d before breeding (DC), 2) ewes maintained across a net wire fence from two vasectomized rams for 15 d before breeding (FC) and 3) ewes maintained approximately 400 m away from rams (NC). At the end of the 15 d, all ewes were placed in one pasture and mated to three fertile Suffolk rams during a 34-d breeding season. A total of 96 Suffolk and 177 Suffolk-cross ewes was utilized during the 3-yr experiment. A greater (P<.05) prebreeding ovulation percentage was observed in DC and FC than in NC ewes. Mating and lambing occurred approximately 6 d earlier for DC or FC ewes than for NC ewes. A similarly designed experiment was conducted using Suffolk and Suffolk-cross ewe lambs allotted to treatments within breed and year to measure effects of ram exposure during the natural breeding season, but prior to breeding. Treatment differences were not detected (P>.05) for date of first observed estrus, date of lambing, percentage of ewes lambing in the first 17 d of the lambing season, number of lambs born per ewe lamb exposed or number of lambs born per ewe lamb giving birth.

¹ Journal paper no. 11059, Purdue Univ. Agric. Exp. Sta.

² Address reprint requests to this author.

³ Present address: Dept. of Anim. Sci., Univ. of Idaho, Moscow 83843.

⁴ Dept. of Anim. Sci. Appreciation is expressed to Dr. G. D. Niswender, Colorado State Univ., for supplying antisera to progesterone. We also thank G. R. Kelly, N. T. Kelly and R. A. Yoder for their assistance with data collection and M. E. Einstein for assistance with statistical analysis. Funded in part by a gift from the Indiana Sheep Breeders Assoc.