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Relationship between sexual behavior classifications of rams and lambs sired in a competitive breeding environment^1,2

J. N. Stellflug^3,*, N. E. Cockett and G. S. Lewis^*

^* USDA-ARS, US Sheep Experiment Station, Dubois, ID 83423; and and Utah State University, Logan, UT 84322-4700

³ Corresponding author: jstellflug{at}pw.ars.usda.gov

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 whitefaced rams classified as female-oriented, with high or low sexual performance, or classified as male-oriented were used in a multiple-sire breeding arrangement. Five groups of approximately 200 ewes each were exposed for 21 d to 3 rams per group consisting of 1 ram from each class. Rams were blocked for sexual class, and those with close 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 4 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 by 1 ram, and 298 had multiples sired by more than 1 ram. The sexual partner preference test used to identify male-oriented rams did not absolutely reflect 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 that 1) sexual partner preference tests used to classify male-oriented rams were not absolute in reflecting their breeding performance in a competitive breeding environment; 2) serving capacity tests predicted that high performance rams would breed more ewes than low performance rams and sire more lambs than either low performance or male-oriented rams; and 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.

Key Words: competitive mating • ewe lambing • lambs born • paternal typing • ram • sexual behavior

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