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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #328815
Title: Do ewes born with a male co-twin have greater longevity with lambing over time?

Author
item GROGEN, DELANE - Wingate University
item BROWN, J. ALISON - Wingate University
item Taylor, Joshua - Bret

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2016
Publication Date: 5/1/2016
Citation: Grogen, D.N., Brown, J., Taylor, J.B. 2016. Do ewes born with a male co-twin have greater longevity with lambing over time?. Journal of Animal Science Supplement. 94(5):9-10.

Interpretive Summary: Based on a recent analysis of historical records, ewes born with a ram as a co-twin had greater lifetime reproductive performance than ewes born with a co-twin ewe. We are interested in determining what component(s) of lifetime reproductive performance may be associated with a ewe’s co-twin sex. As an initial indicator of longevity in the flock, we hypothesized that co-twin sex will affect the number of years a ewe remains in the flock as a productive ewe, or in other words, giving birth every year throughout her lifetime. Using the USDA, ARS, US Sheep Experiment Station database, lambing records from 1994 to 1997 were queried of ewes that were either born with a male or female co-twin. A total of 4,442 ewes were identified, and breeds included Columbia, Polypay, Rambouillet, and Targhee. Based on the data, the sex of the ewe’s co-twin did not influence the years that a ewe remained in the flock as a productive ewe. Therefore, we concluded that the positive effect of a ewe being born with a co-twin male is more likely associated other factors of reproductive performance, such as ovulation rate.

Technical Abstract: Based on a recent analysis of historical records, ewes born co-twin to a ram had greater lifetime reproductive performance than ewes born co-twin to a ewe. We are interested in determining what component(s) of lifetime reproductive performance may be associated with a ewe’s co-twin sex. As an initial indicator of longevity in the flock, we hypothesized that co-twin sex will affect the age at which ewes consistently appear in the lambing records (i.e., recorded as having lambed). Therefore, the objective was to determine the percentage of ewes, born with a female or male co-twin, that appear in the lambing records at ages 2 to 7 yr. Using the USDA, ARS, US Sheep Experiment Station database, lambing records from 1994 to 1997 were queried of ewes that were either born with a male or female co-twin. A total of 4,442 ewes were identified, and breeds included Columbia (n = 417), Polypay (n = 627), Rambouillet (n = 446), and Targhee (n = 427). For each age class, Chi square analysis was used to compare the expected percentage of ewes lambing that were either born to a female or male co-twin. Of ewes born as a twin and subsequently recorded as having lambed, we expected that within each age class (2 to 7 yr) 50% of the ewes were originally born as a female co-twin to a female (FF) and 50% born as a female co-twin to a male (FM). The observed percentage of FF (52.7%) or FM (47.3%) ewes did not differ, regardless of age or breed ('2 = 52.3,df 41, a = 0.05, p = 0.11). Within breed, no differences between percentages were observed in Columbia (FF = 53.8% and FM = 46.2%; '2 = 52.9, df = 41, a = 0.05, p = 0.11), Rambouillet (FF = 55.2% and FM = 44.8%; '2 = 34.2, df = 39, a = 0.05, p = 0.69), and Targhee (FF = 46.3% and FM = 53.7%; '2 = 45.5, df 41, a = 0.05, p = 0.36) ewes regardless of age. However, Polypay ewes had a greater female to male co-twin ratio (FF = 54.6% and FM = 45.4% ; '2 59.2, df =41, a = 0.05, p = 0.03) regardless of year and at age 2 (FF = 55% and FM =45% ; '2 = 15.7, df =5, a = 0.05, p = 0.008), but no differences were found at any other age. Data suggested the ratio of ewes having a female or male co-twin did not vary from the expected ratio, thus ewes having a male co-twin did not have greater longevity with lambing compared to ewes with a female co-twin. However, this ratio may be influenced by breed.