154 Growth, Libido, Semen Quality, and Reproductive Organ Weights of Hair Sheep Rams Rendered Short-Scrotum at Birth or Weaning

Abstract

Abstract Rendering male lambs short-scrotum interferes with testicular development and thermoregulation, and has been proposed as a management tool to control male reproduction. This study evaluated at the effect of timing of the procedure (birth or weaning) on growth rate, testis size, libido, ejaculate characteristics and carcass traits in male landrace hair sheep lambs. April- (n = 31) and August-born (n = 23) Barbados Blackbelly (BB) and St. Croix (SC) male hair sheep lambs, balanced by breed and birth type, were rendered short-scrotum (SS) using elastrator bands at birth (B) or weaning (W), or left intact (I). Lambs were born on pasture, weaned at 9 weeks, transitioned in pens for two months post weaning, and then rotationally grazed as a single group to a target weight of 40 kg. At 6-mo of age (peri-pubertal), and again at target weight (post-pubertal), mating behavior was recorded (day) and ejaculate samples collected (day 2). Mating behavior was recorded in a0-min test with males individually exposed to estrus-induced ewes pen. An initial attempt was made to collect semen using an estrus-induced teaser ewe, and if not successful, the semen sample was collected by electro-ejaculation. At target weight lambs were harvested, scrotal content collected, and carcass characteristics (April cohort) determined. Data were analyzed in a model with sex class, breed and cohort as main effects. Pen and pasture ADG (142 and 129 g/d, respectively) and age at target weight (287 d) was not affected (P > 0.1) by SS treatment. However, April-born lambs grew 19 g/d less (P < 0.01) and reached target weight 40 d later (P < 0.001) than August-born males. As for breed, STX had greater pasture ADG (139 vs 124 g/d; P < 0.05) and reached target age 19 days earlier (P< 0.05) than BB males. Libido (number of mounts and services) was not affected by SS treatment, breed or cohort. The frequency of ejaculates containing sperm was less (P < 0.001) in SS (26 to 33%) than intact males (97%) and increased with age in SS but not I males. Sperm concentration and motile sperm in ejaculates were greater (P< 0.05) in I than SS males. Testis and epididymis were larger (P < 0.001) in I (300 and 44.3 g) than in B (134 and 20.0 g) and W (154 and 23.8 g), which were not different. Cohort and breed had no effect (P > 0.1) on mating behavior, ejaculate characteristics, and organ weights. Results suggest that SS and its timing had no effect on growth rate or on mating behavior. Though the procedure depressed the presence of sperm in the ejaculate and decreased testis weight, the suppression was not complete, and caution is warranted in utilizing the technique to facilitate co-grazing ewe lambs.