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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Genetics and Animal Breeding » Research » Publications at this Location » Publication #170597
Title: INFLUENCE OF BODY WEIGHT, AGE, AND WEIGHT GAIN ON FERTILITY AND PROLIFICACY IN FOUR BREEDS OF EWE LAMBS

Author
item GASKINS, CHARLES - WASHINGTON STATE UNIV.
item Snowder, Gary
item WESTMAN, M. - BURNABY, BC, CANADA
item EVANS, M. - WASHINGTON STATE UNIV.

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2005
Publication Date: 7/3/2005
Citation: Gaskins, C.T., Snowder, G.D., Westman, M.K., Evans, M. 2005. Influence of body weight, age, and weight gain on fertility and prolificacy in four breeds of ewe lambs. Journal of Animal Science. 83:1680-1689.

Interpretive Summary: Reproduction is an important economic trait in sheep production. However, the reproductive performance of young ewes is typically much less compared to older ewes. Breeding ewes to lamb at 1 yr of age can significantly improve profitability for most sheep production systems. The main objective of this study was to evaluate the effect of age and weight on reproductive performance of ewe lambs. A second objective was to compare the effects of weight and age variables in four major sheep breeds (Columbia, Polypay, Rambouillet, and Targhee). A very large and reliable data set from the U.S. Sheep Experiment Station, Dubois, ID collected from 1984 through 1988 was analyzed. The results indicated that significant differences among breeds for fertility rates of young ewe lambs exist. The Polypay breed had an adjusted average fertility rate of 93% compared with lower fertility rates in Columbia, Targhee, and Rambouillet ewe lambs (50, 60, and 75%, respectively). Percent of multiple births, a measure of prolificacy, was also significantly higher in the Polypay (47%) than Columbia, Targhee, and Rambouillet (1, 13, and 14%, respectively). Production systems influenced by ewe lamb reproductive ability may desire to select the Polypay over other breeds. It was also found that heavier body weights of ewe lambs at breeding had a positive effect on fertility and percent of multiple births. Total weight gain of ewe lambs from weaning to breeding had positive effect only on fertility. When age and weight traits were analyzed within each breed, effects of age and weight varied among breeds. Increasing weight at breeding increased the probability of pregnancy in Rambouillet and Targhee ewe lambs. The probability of multiple births increased with age in the Rambouillet. Increasing weight at breeding significantly increased the probability of multiple births in all breeds. In conclusion, Polypay ewe lambs were superior in fertility and prolificacy to Columbia, Rambouillet, and Targhee under western range conditions. The manuscript provides estimates for age and weight thresholds that sheep producers may consider to improve reproductive performance of Columbia, Rambouillet, and Targhee ewe lambs.

Technical Abstract: Breeding ewes to lamb at 1 yr of age can significantly improve profitability for some production systems. The objective of this study was to evaluate the effect of age and weight at breeding and total post weaning weight gain on reproductive performance of ewe lambs. A second objective was to compare the effects of weight and age variables in four major sheep breeds (Columbia, Polypay, Rambouillet, and Targhee). Weights, ages, and the binary traits of fertility (pregnant or non-pregnant) and prolificacy (1 lamb born versus 2 or more) were collected on 2,055 ewe lambs at the U.S. Sheep Experiment Station, Dubois, ID from 1984 through 1988. The effects of age and weight at breeding and total weight gain from weaning to breeding on fertility and prolificacy were analyzed with a logit model in maximum likelihood analyses. Significant differences among breeds for fertility were identified with 93% fertility for Polypay ewe lambs compared with lower fertility rates in Columbia, Targhee, and Rambouillet ewe lambs (50, 60, and 75%, respectively). Percent of multiple births (prolificacy rate) was also significantly higher in the Polypay (47%) than Columbia, Targhee, and Rambouillet (1, 13, and 14%, respectively). Averaged across breeds, weight at breeding had a positive effect on fertility and prolificacy (P < 0.01), while total weight gain from weaning to breeding had positive effect only on fertility (P < 0.02). In separate analyses for each breed, increasing age and weight at breeding increased the probability of pregnancy in Rambouillet ewe lambs. The probability of pregnancy for Targhee ewe lambs increased with weight at breeding (P < 0.05). Increasing weight at breeding significantly increased the probability of multiple births in all breeds. Increasing total post weaning weight gain significantly increased the probabilities of multiple births in Rambouillet and Targhee ewe lambs. In conclusion, Polypay ewe lambs were superior in fertility and prolificacy to Columbia, Rambouillet, and Targhee under western range conditions. Improved reproductive performance of Columbia, Rambouillet, and Targhee ewe lambs may be achieved by increasing age and weight at breeding, and post weaning gain.