EFFECT OF EARLY AND LATE EXPOSURE TO ESTRUAL EWES ON RAM SEXUAL PERFORMANCE CLASSIFICATIONS.

Authors: Stellflug, John; Lewis, Gregory

Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2006
Publication Date: 2/10/2006
Citation: Stellflug, J.N., Lewis, G.S. 2007. Effect of early and late exposure to estrual ewes on ram sexual performance classifications. Animal Reproduction Sciences. 97:295-302.

Interpretive Summary: The early exposure of 7 to 8 mo-old ram lambs to estrual ewes improves sexual performance in serving capacity tests at 16 to 19 mo of age in most rams. However, a late exposure of 3 d just before the sexual performance tests had minimal influence on sexual performance. The combination of early and late exposure to estrual ewes was similar to results with early exposure alone. Thus early exposure was more important than the late exposure to estrual ewes for improving sexual performance test scores. This technique helps reduce the number of serving capacity tests required to identify high sexual performance rams that breed approximately twice as many ewes and sire twice as many lambs as low performance rams.

Technical Abstract: This study was conducted to determine whether exposure of ram lambs to estrual ewes during their first autumn and again as adults just before serving capacity tests (SCT) affected the outcome of the sexual performance tests. Treatments were either early exposure of Polypay ram lambs (i.e., 7- to 8-mo-old rams with ewes for 17 d [EXE; n = 30] or no exposure early [N-EXE; n = 30]), and late exposure (i.e., 16- to 19-mo-old rams with ewes for 3 d [EXL]) or no exposure [N-EXL] to estrual ewes in a 2 x 2 factorial arrangement (EXE + EXL, EXE + N-EXL, N-EXE + EXL, N-EXE + N-EXL). Three SCT with induced estrual ewes were conducted immediately after the early exposure period for individual EXE rams. Three sham sexual performance tests (i.e., 3 ram lambs placed in test pens for 30-min without ewes) were conducted with N-EXE rams. Both groups of rams were given SCT at 16- to 19-mo of age to determine sexual performance. Just before nine 30-min SCT, one half of the rams from each early exposure treatment were assigned to late exposure treatments (i.e., exposure vs. no exposure). Specific sexual behaviors (e.g., sniffs, flehmens, foreleg kicks, vocals, mount attempts, mounts, and ejaculations) were recorded during the 9 SCT. The sniffs, flehmens, foreleg kicks, vocals, and mount attempts were added without being weighted and analyzed as courtships. Sexual performance data were analyzed with Mixed model procedures for repeated measures. During SCT, the early exposed rams (EXE) rams exhibited more courtships (40.3 ± 8.0 vs 23.4 ± 4.6; P < 0.05; LSM ± estimated SE), mounts (11.3 ± 1.0 vs 7.7 ± 0.9; P < 0.01), and ejaculations (2.4 ± 0.2 vs 1.5 ± 0.2; P < 0.01) than the not exposed early rams, respectively. The main effect for late exposure was not significant. We conclude that early exposure of 7- to 8- mo-old ram lambs to estrual ewes improves sexual performance in SCT at 16- to 19-mo of age in most rams. Late exposure to estrual ewes 3 d before SCT did not improve sexual performance scores. Thus early exposure was a more important experience than late exposure to estrual ewes for improving ram sexual performance in serving capacity tests.