Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/10/2005
Publication Date: 4/2/2005
Citation: Stellflug, J.N., Cockett, N.E., Lewis, G.S. 2005 The relationship between sexual behavior classifications of rams and lambs sired in a competitive breeding environment. Proceedings of the Western Section of the American Society of Animal Science. 55:65-68. Interpretive Summary: The relationship of three different classifications of rams and lambs sired were determined in a competitive breeding environment to evaluate ram sexual behavior tests. The individual sexual partner preference tests conducted with two restrained rams and two restrained estrual females did not predict breeding performance of male-oriented rams. However, serving capacity tests conducted with three unrestrained estrual ewes did predict breeding performance of high and low sexual performance female-oriented rams. Exclusively male-oriented rams, as identified in sexual partner preference tests before the breeding trial, bred ewes under competitive conditions, sired as many lambs as low sexual performance rams, but did not sire as many lambs as high sexual performance rams. Thus sexual partner preference tests used to identify male-oriented rams did not predict breeding performance in a competitive breeding environment. Serving capacity tests can be used to classify high and low sexual performance rams and show a close relationship to breeding performance. Under the conditions of this study where 10 to 12 ewes needed to be serviced daily in each breeding pen, low performance and male-oriented rams did not have an adverse impact on the outcome of the breeding period because together low performance and male-oriented rams bred as many ewes as the high performance ram alone. Therefore, we suggest that serving capacity tests should be used to select high performance rams and reduce the number of rams with marginal sexual performance.
Technical Abstract: The objective for this study was to determine the relationship between three sexual classes of rams and lambs sired in a competitive breeding environment. Fifteen, 2- to 3-yr-old white-face rams classified as female-oriented, with high (HPFOR) or low (LPFOR) sexual performance, or male-oriented (MOR) were used in a multiple-sire breeding arrangement. Five flocks of approximately 200 ewes each were exposed for 21 d to three rams per flock consisting of one ram from each of the classes. Rams were initially blocked for sexual class, and those with similar genetic relationships were assigned to different pens. Genomic DNA was prepared from blood collected from rams, ewes, and lambs. Up to four microsatellite markers were used to assign sire parentage within pens. Sexual partner preference tests (PREFT) used to identify MOR did not accurately predict sexual performance during competitive breeding. In contrast to only mounting and servicing males in PREFT before breeding, MOR sired 480 lambs from 330 ewes. Serving capacity tests (SCT) predicted sexual performance of HPFOR and LPFOR. The HPFOR impregnated more ewes (499 vs 258; P < 0.05) and sired more lambs (756 vs 357; P < 0.05) than LPFOR, respectively. The LPFOR and MOR did not differ for ewes impregnated or lambs sired. We conclude 1) that the PREFT used to classify MOR did not predict their breeding performance in competitive breeding; 2) that SCT did predict that HPFOR rams would impregnate more ewes than LPFOR and sire more lambs than did either LPFOR or MOR; and 3) under conditions of this study, LPFOR and MOR did not have an adverse impact on the overall breeding outcome. Combined LPFOR and MOR sired as many lambs as HPFOR, thus requiring twice as many rams to obtain equivalent breeding results as HPFOR. Therefore, we suggest that SCT should be used to select HPFOR and reduce the number of rams with marginal sexual performance.