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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #138441
Title: INFLUENCE OF CLASSIFICATION LEVELS OF RAM SEXUAL ACTIVITY ON SPRING BREEDING EWES

Author
item Stellflug, John

Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2002
Publication Date: 4/15/2002
Citation: Animal Reproduction Sciences. 2002. v. 70. p. 203-214.

Interpretive Summary: We used Polypay ram lambs (7 to 8 months of age) and mature rams (19 to 20 months of age) to evaluate effect of level of male sexual performance on reproduction of Polypay ewes at spring breeding when reproduction is generally reduced because of seasonal effects. The sexual performance score of males was determined by observing the number of ejaculations during 7 to 18, 30-minute tests with ewes in estrus from January to early March before a late March to April breeding time. In the first study, ram lambs with high and low sexual performance scores (high performance and low performance) were individually exposed to approximately 30 Polypay ewes. In the second two studies, high and low performance mature rams were individually exposed to approximately 30 Polypay ewes for two years in each study. In Expt. 1, lambing rates using high versus low performance ram lambs did not differ (65.8 versus 53.0, respectively). Prolificacy was increased by 0.1 lambs in ewes bred by low performance ram lambs. Total number of lambs born per ewe present at lambing, and lambing distribution were not altered by high and low performance ram lambs. In Expt. 2, lambing rates using high versus low performance mature rams did not differ (58.7 versus 60.1). In Expt.3, lambing rates using high versus low performance mature rams did not differ (74.3 versus 69.0). In addition, high compared to low performance mature rams did not affect other reproductive variables. Present studies indicate that high and low performance ram lambs and mature rams did not alter lambing rates or lambing distribution in late March to April. Thus, high and low performance, Polypay rams and ram lambs that are sexually active and have average quality semen can provide a source of rams for ambient spring breeding but there was no advantage to using high performance instead of sexually active low performance ram lambs or rams.

Technical Abstract: Polypay ram lambs (7 to 8 mo) and mature rams (19 to 20 mo) were used to evaluate effect of level of male sexual performance on reproduction of Polypay ewes at spring breeding. In Expt. 1, ram lambs with high (1.8 +/- 0.3; n = 5) and low (0.9 +/- 0.2; n = 5) sexual performance scores (HP and LP; mean " SEM) were used in single sire breeding. Ewes (n = 305) were stratified by age to pens. For Expt. 2 and 3, two replicates were conducted with mature rams in single sire pens. For Expt. 2, HP rams (n = 5) had 3.2 to 4.1 +/- 0.2 and LP rams (n = 8) had 1.7 to 1.9 "0.4 sexual performance scores based on 9, 30-min serving capacity tests (SCT). Ewes (n = 152 to 153/yr) were stratified by age to pens. For Expt. 3, HP rams (n = 6) had 3.6 to 3.8 +/- 0.2 and LP rams (n = 10) had 2.1 to 2.5 +/- 0.1 sexual performance scores based on 18, 30-min SCT. Ewes (n = 229 in 1996 and 244 in 1997) were stratified by age to breeding pens. In Expt. 1, lambing rates using HP vs. LP ram lambs did not differ (65.8 vs. 53.0; P = 0.20). Prolificacy tended (P = 0.06) to be increased by 0.1 lambs in ewes bred by LP ram lambs. Total number of lambs born per ewe present at lambing, and lambing distribution were not altered by HP and LP ram lambs. In Expt. 2, lambing rates using HP vs. LP mature rams did not differ (58.7 vs. 60.1; P = 0.78). In Expt.3, lambing rates using HP vs. LP mature rams did not differ (74.3 vs. 69.0; P = 0.35). There was no difference (P > 0.10) between years for Expt. 2 or Expt. 3 and mature HP and LP rams did not affect the other reproductive variables monitored. Analysis of the combined data for Expt. 2 and 3 indicated only a year difference (P < 0.001) in lambing rates and total lambs born. Present studies indicate that HP and LP ram lambs and mature rams did not alter lambing rates or lambing distribution in late March to April. Thus, HP and LP, Polypay rams and ram lambs that are sexually active and have average quality semen can provide a source of rams for ambient spring breeding but there was no advantage to using HP instead of sexually active LP ram lambs or rams.