The influence of breeding intensity on above- and below-average sexual performance rams in single- and multiple-sire breeding environments.

Authors: Stellflug, John; COCKETT, NOELLE - UTAH STATE UNIVERSITY; Lewis, Gregory

Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2007
Publication Date: 8/7/2007
Citation: Stellflug, J.N., Cockett, N.E., Lewis, G.S. 2007.The influence of breeding intensity on above- and below-average sexual performance rams in single- and multiple-sire breeding environments. Animal Reproduction Sciences. doi:10.1016/j.anireprosci.2007.02.017

Interpretive Summary: Sexual classifications based on serving capacity tests are related to the breeding performance of rams in certain breeding environments. When breeding intensity is high, rams ranked above the average serving capacity test scores impregnate more ewes and sire more lambs than rams ranked below the average test scores. When only a small number of ewes are in estrus daily, below-average rams perform as well as above-average rams in multiple-sire breeding and single-sire breeding environments. We suggest that, when breeding intensity is expected to be high, serving capacity tests should be used to select above-average serving capacity rams so that the number of rams required to impregnate a large number of ewes during a brief breeding period can be reduced.

Technical Abstract: Two studies were conducted to evaluate the relationship between serving capacity scores and breeding performance of rams. The first study was conducted to determine whether rams with above or below mean serving capacity scores could perform equally in high and low breeding intensity, single-sire mating schemes. The second study was conducted to determine whether rams with above and below mean serving capacity scores could perform equally well when only one or two ewes were in estrus daily in a multiple-sire breeding scheme (two rams/pen). Rams (n = 68) were ranked according to average number of ejaculations recorded in serving capacity tests. Sixteen rams with highest scores (above-average) and 16 rams with lowest scores (below-average) were identified for breeding. Half of above-average and half of below-average rams were used in the two studies. For Study 1, each ram was individually introduced to 23 estrus-induced ewes for 9 d to simulate high breeding intensity. Rams were given a 5-d rest before they were individually introduced to 23 to 24 naturally cyclic ewes for 17 d (low breeding intensity). For Study 2, 16 rams were paired across ram types, and each pair competed for 20 ewes for 18 d (8 pens). For Study 1, ewe fertility (ewes lambing/ewes present at lambing) and number of lambs born was greater (P < 0.001) for above-average (0.67 ± 0.03 and 27.6 ± 1.2, respectively) than for below-average rams (0.39 ± 0.07 and 15.3 ± 2.7) with high breeding intensity. Ewe fertility and lambs born did not differ for above-average (0.91 ± 0.03 and 37.8 ± 1.9, respectively) and below-average rams (0.86 ± 0.03 and 39.0 ± 1.9) with low breeding intensity. For Study 2, number of ewes lambing (99 ± 8.0 versus 72 ± 13.6; P = 0.12) and number of lambs sired (148 ± 18.3 versus 101 ± 22.8; P = 0.15) did not differ between above- and below-average rams, respectively, in direct competition. Sexual classifications based on serving capacity tests are related to breeding performance of rams in certain breeding environments. When breeding intensity is high, above-average rams impregnate more ewes and sire more lambs than below-average rams. When only a small number of ewes are in estrus daily, below-average rams perform as well as above-average rams in multiple-sire and single-sire breeding environments. We suggest that above-average rams should be used to reduce number of rams required when breeding intensity is high.