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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #148327
Title: GENETIC CORRELATION OF RAM SEXUAL PERFORMANCE WITH EWE REPRODUCTION TRAITS FOR FOUR SHEEP BREEDS

Author
item Snowder, Gary
item Stellflug, John
item Van Vleck, Lloyd

Submitted to: Applied Animal Behaviour Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2004
Publication Date: 4/13/2004
Citation: Snowder, G.D., Stellflug, J.N., Van Vleck, L.D. 2004. Genetic correlation of ran sexual performance with ewe reprodictive traits of four sheep breeds. Applied Animal Behaviour Science. 88:253-261.

Interpretive Summary: Sexually mature rams can be classified by their level of sexual activity when exposed to breeding ewes. Differences between high and low sexually active rams have been shown to be genetically influenced. This study determined if ewe reproduction can be genetically improved by selecting rams for their sexual activity classification. Statistical analyses were performed on a large data set of 4,685 records for sexual performance scores of rams and 35,154 records of reproductive performance of ewes from four sheep breeds. The genetic relationship between ram sexual activity and ewe reproductive traits was near zero for most breeds. Direct selection of the ewe to increase reproductive rate is a more practical approach than selecting for rams with high sexual activity at mating.

Technical Abstract: Rams express differences in sexual performance during the breeding season. Breeding rams with high sexual performance scores as measured during a sexual performance test can improve flock fertility. Whether selecting rams for high sexual performance score will indirectly improve ewe reproductive performance is not known. The objective of this study was to estimate the genetic correlation between sexual performance scores of rams and reproduction of ewes. Sexual performance scores of rams and reproductive performance (number of lambs born per ewe exposed and number of lambs weaned per ewe exposed) from four breeds were analyzed with univariate and bivariate animal models using REML. A total of 4,685 records for sexual performance scores of rams were obtained from the U.S. Sheep Experiment Station (Columbia, n = 807; Polypay, n = 1,668; Rambouillet, n = 1,208; and Targhee, n = 1,002). Reproductive performance of ewes was based on 35,154 records (Columbia, n = 7,693; Polypay, n = 9,229; Rambouillet, n = 10,954; and Targhee, n = 7,278). Estimates of heritability for sexual performance score of rams were larger for the Columbia (0.31 ± 0.09) and Polypay (0.30 ± 0.08) than that for Rambouillet (0.14 ± 0.07) and Targhee breeds (0.17 ± 0.08). Overall breed heritability estimate was 0.22 ± 0.04. Heritability estimates for number of lambs born were larger (0.05 to 0.11) than for number of lambs weaned (0.02 to 0.05). Estimates of genetic correlation between sexual performance score and number of lambs born were near zero (-0.09 to 0.02) except for the Columbia breed (rg = 0.24 ± 0.20). Estimates of genetic correlation between sexual performance score of the ram and number of lambs weaned varied by breed (Columbia, 0.28 ± 0.26; Polypay, 0.00 ± 0.25; Rambouillet, -0.17 ± 0.25; and Targhee, 0.32 ± 0.28). Overall breed genetic correlations of sexual performance of rams with number of lambs born and weaned were 0.00 ± 0.10 and 0.00 ± 0.12, respectively. Because of the low heritability of ewe reproductive traits and their apparently nil to low genetic correlation with sexual performance scores of rams, selection and use of rams with high sexual performance scores would not be expected to result in much indirect response for improved reproduction of ewes.