Ewe productivity and subsequent preweaning lamb performance in St. Croix sheep bred at different times during the year.
Seasonality of breeding was evaluated in 165 purebred St. Croix ewes over a period of 3 yr at a latitude of 35 degrees 6' N. Ewes were divided into six groups for breeding starting in August of 1989 and a group was exposed to rams every 2 mo throughout the experiment. Lambing percentage was lowest for spring breeding (P < .01), which resulted in lower numbers born and weaned per ewe exposed (P < .01) and lower litter birth and weaning weights per ewe exposed (P < .01). Except as compared with late winter breeding, number born per ewe lambing was also lower for the spring breeding (P < .01), indicating potentially lower ovulation rates at that time or higher embryonic losses through summer gestation. Mean litter weaning weights were lower for spring and fall breeding seasons (P < .05), probably due to lowered forage availability and quality during the preweaning period for these lambs. These data indicate that St. Croix are sufficiently aseasonal to be of benefit in an accelerated lambing program.
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South Central Family Farm Research Center, ARS, USDA, Booneville, AR 72927, USA.
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D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001131:Arkansas; D001724:Birth Weight / Q000502:physiology; D001947:Breeding; D005260:Female; D008297:Male; D012098:Reproduction / Q000502:physiology*; D012621:Seasons; D012756:Sheep / Q000254:growth & development / Q000502:physiology*