Effects of genotype, nutrition, and progesterone on uterine efficiency in the ewe Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dr26z268v

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  • Embryonic loss of potential lambs resulting in partial failure of multiple ovulations is a significant factor in the reproductive rate of prolific breeds. The roles of genetic and nutritional variation (and their possible interaction) on embryonic loss were studied by mating blackface and whiteface ewes of either high or low body condition to either Suffolk or Polypay rams. Variation in body condition was created by placing ewes on either high or low planes of nutrition for 13 weeks prior to breeding and the first 30 days of pregnancy with the goal of achieving mean body condition scores of 4.0 and 2.5, respectively. Low ewes were flushed to overcome expected depression in ovulation rate due to poor body condition. The actual difference achieved was 1.0 condition score units (and 11 kg) at the commencement of mating. Embryo loss was defined as difference between ovulation rate as measured by laparoscopy shortly post-mating, and litter size at term. Mean ovulation rate for ewes conceiving to first estrus was 2.34 for whiteface ewes and 2.02 for blackface ewes (p<.05). Mean ovulation rates for High and Low ewes were 2.10 and 2.20, respectively (p=.32). The potential role for progesterone insufficiency during critical times in early gestation was assessed from plasma samples collected at days 13 and 20 of gestation, and analyzed from ewes exhibiting embryo loss and contemporary ewes without loss. There was no evidence that genotype of either ewes or embryos, nutritional status, or progesterone levels had an effect on uterine efficiency in either twin- or triple-ovulating ewes. Plasma progesterone concentrations were affected by a genotype by ovulation rate interaction at both day 13 (p=.04) and at day 20 levels (p<.01). Day 20 concentrations were also affected by a genotype by litter size interaction (p<.01).
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