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Effects of Plane of Nutrition and Phenobarbital During the Pre-Mating Period on Reproduction in ewes Fed Differentially During the Summer and Mated in the Fall

University of Illinois^3,4,, Urbana 61801

Abstract

An increased plane of nutrition of ewes before mating (flushing) has been associated with an increased number of lambs per ewe. The following study was done to investigate a possible mechanism for the flushing effect. During the summer, 98 Hampshire and Suffolk ewes grazed pastures with 50 of the ewes supplemented with .45 kg of corn grah·head_–1 ·d_–1. For approximately 12 d before fall mating, each ewe received daily either .45 kg of a corn grain-soybean oil meal mixture, an oral dose of 1 g phenobarbital or no treatment. Liver biopsies were collected from 23 ewes, representing all treatment combinations, 3 d after initiation of pre-mating treatment for determination of concentration of hepatic mixed function oxidase enzymes (MFO). Summer supplementation vs no summer supplementation resulted in ewes with heavier (P<.05) body weights near mating (75.6 vs 71.1 kg), higher (P<.01) mating condition scores (3.2 vs 2.9), a greater (P<.01) number of ovulations (1.99 vs 1.74), but little difference (P>.10) in number of lambs born per ewe lambing. Pre-mating treatment with phenobarbital or grain mix resulted in a greater number of ovulations (P<.01, P<.10, respectively) than no pre-mating treatment (2.14, 1.85, 1.60; respectively). Ewes given phenobarbital had more (P<.10) lambs per ewe than ewes given no treatment (1.71 vs 1.40). Both phenobarbital and grain mix resulted in a significant increase in concentration of MFO compared with no treatment. The flushing response may be associated with an increased concentration of MFO, which could increase the metabolism of steroids, lessening the inhibition to the hypothalamic-pituitary axis, and result in the secretion of more gonadotropins and an increased number of ovulations and lambs.

¹ Present address: Univ. of Arkansas Med. School, 4301 W. Markham St., Slot 518, Little Rock, AR 72205.

² Present address: Rt. 2, Box 34A, Centreville, MD 21617.

³ Dept. of Anim. Sci., 1207 W. Gregory Drive.

⁴ Leroy McFarland is acknowledged and thanked for care of experimental animals and Annette F. Holland, A. Carol Collins and Cathy Ndekwe for manuscript preparation.