458 - Growth Performance of Short Scrotum and Castrated Hair Sheep Lambs on Pasture During Different Seasons

Castrated lambs tend to grow slower compared to intact males. Rendering lambs short scrotum offers an opportunity to achieve comparable growth to an intact lamb while allowing them to be co-grazed with ewe lambs. Here we evaluated lamb growth in a mixed flock of castrated (CA), short-scrotum (SS) and female (FE) Barbados Blackbelly and St. Croix hair sheep lambs. Lambs were born in December (n = 30) and April (n = 45) from the same ewe flock mated to different sires each season. Ram lambs were either rendered short scrotum or completely castrated using elastrator bands at weaning, and all lambs transitioned in dry lot for 2 mo before return to pasture. Lambs co-grazed in a rotational pasture system and were moved based on visual assessment of forage availability and were provided bermudagrass hay when forage availability was limited. Lambs were supplemented with soy hull at 3% BW to ensure diet continuity between forage environments. Ewe lambs were grown to target weights of 35 kg and males to 40 kg. Data were analyzed for sex class, breed, and season as main effects. Pasture ADG was higher (P < 0.001) in SS (132 g/d) than in CA (102 g/d) and FE (96 g/d) lambs. Age at target weight tended to be earlier (P < 0.1) in SS (261 d) than CA (291 d). December-born lambs had higher pen ADG (236 vs. 135 g/d; P< 0.001) than April-born lambs, but had similar pasture ADG (102 vs. 108 g/d). In contrast, St. Croix lambs had similar pre-pasture growth to Blackbelly lambs, but higher pasture ADG (118 vs. 94 g/d; P < 0.001) and reached target weight 40 d earlier (P < 0.001). Data indicate that the forage environment allowed differences in growth potential derived from sex type and breed to be expressed, but that soy hull supplementation likely masked seasonal differences associated with forage quality.