Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/14/2005
Publication Date: 2/8/2006
Citation: Stellflug, J.N., Cockett, N.E., Lewis, G.S. 2006. The relationship between sexual behavior classifications of rams and lambs sired in a competitive breeding environment. Journal of Animal Science. 84:463-468. Interpretive Summary: This research indicates that individual sexual partner preference tests do not predict breeding performance of male-oriented rams. However, individual serving capacity tests do predict breeding performance of high and low sexual performance female-oriented rams. Exclusively male-oriented rams, as identified in preference tests before a breeding trial, will breed ewes under competitive conditions, sire as many lambs as low performance rams, but not sire as many lambs as high performance rams. Combined, low performance and male-oriented rams may breed as many ewes and sire as many lambs as a single high performance ram. Therefore, we suggest that serving capacity tests should be used to select high performance rams, reduce the number of rams with marginal sexual performance, and make decisions on the number of rams needed.
Technical Abstract: The objectives for this study were to 1) determine the relationship between sexual performance class and lambs sired in a competitive mating environment and 2) determine whether the male-oriented ram test is valid. Fifteen 2- to 3-yr-old white-faced rams classified as female-oriented, with high or low sexual performance, or male-oriented were used in a multiple-sire breeding arrangement. Five groups of approximately 200 ewes each were exposed for 21 d to three rams per group consisting of one ram from each class. Rams were blocked for sexual class, and those with similar genetic relationship were assigned to different pens. Genomic DNA was prepared from blood collected from 15 rams, 934 ewes, and 1,757 lambs. Up to four microsatellite markers were used to determine a lamb’s sire. Of 884 ewes with identifiable lambs (known sires), 178 ewes had single lambs, 408 had multiples sired with one ram, and 298 had multiples sired with more than one ram. Sexual partner preference test used to identify male-oriented rams did not accurately predict their sexual performance during competitive breeding. In contrast to only mounting and servicing males in preference tests before breeding, male-oriented rams sired 480 lambs from 330 ewes. Serving capacity tests predicted sexual performance of high and low sexual performance rams. High performance rams impregnated more ewes (499 vs. 258; P < 0.05) and sired more lambs (756 vs. 357; P < 0.05) than did low performance rams, respectively. Low performance and male-oriented rams did not differ for ewes impregnated or lambs sired. We conclude 1) that sexual partner preference tests used to classify male-oriented rams did not predict their breeding performance in a competitive breeding environment; 2) that serving capacity tests did predict that high performance rams would impregnate more ewes than low performance rams and sire more lambs than either low performance or male-oriented rams; 3) under the conditions of this study, low performance and male-oriented rams did not have an adverse impact on the overall breeding outcome. Combined, low performance and male-oriented rams sired 81 more lambs than did high performance rams, but this required twice as many rams to obtain approximately equal breeding results. Therefore, we suggest that serving capacity tests should be used to select high performance rams, reduce number of rams with marginal sexual performance, and make decisions on ram numbers needed.