Ewe fertility in the STAR accelerated lambing system

• Published in: Journal of animal science 1996-07, Vol.74 (7), p.1511-1522
• Main Authors: Lewis, R. M, Notter, D. R, Hogue, D. E, Magee, B. H
• Format: Article
• Language: English
• Subjects: Aging - physiology; Animal Husbandry - methods; Animal Husbandry - standards; Animal productions; Animal reproduction; Animals; Biological and medical sciences; brebis; Breeding - methods; Breeding - standards; breeding seasons; breeds animals; critere de selection; criterios de seleccion; Environment; epoca de apareamiento; ewes; Female; Fertility; Fertility - physiology; forecasting; Fundamental and applied biological sciences. Psychology; lactation number; Linear Models; Male; Models, Biological; new york; nueva york; numero de lactacion; numero de lactation; oveja; parto; parturition; performance de reproduction; Periodicity; Pregnancy; puerperio; puerperium; race animal; razas animales; reproductive performance; reproductividad; saison d' accouplement; seasonal variation; Seasons; selection criteria; Sheep; Sheep - genetics; Sheep - physiology; technique de prevision; tecnicas de prediccion; Terrestrial animal productions; Time Factors; variacion estacional; variation saisonniere; Vertebrates
• ISSN: 0021-8812; 1525-3163; 0021-8812
• DOI: 10.2527/1996.7471511x

Effects of environmental factors such as ewe age, season of exposure, and time from lambing to exposure on fertility were evaluated using records on 1,084 Dorset ewes in the STAR accelerated lambing system. The STAR program consisted of five 30-d concurrent breeding and lambing periods per year beginning on January 1, March 15, May 27, August 8, and October 20. Fertility in the flock changed in a cyclic and predictable fashion during the year. Changes in prolificacy were less consistent but also tended to show cyclic variation. Matings that occurred within the typical breeding season (August, October, and January) were more fertile than those occurring in March and June. However, fertility also varied with the age of the ewe and the time since the ewe's last lambing. Except in June, fertility at the first postpartum mating increased as ewes aged. In March and June matings, adult ewes that had just weaned lambs were less fertile than ewes that had failed to conceive in the previous season and therefore had longer postpartum intervals. However, in October and January, ewes that had just weaned lambs were more fertile. A matrix of expected pregnancy rates, or probabilities of fertility, was constructed using a mixed GLM to describe the combined effect of season, ewe age, and time since lambing on ewe fertility in accelerated lambing.