96. Agro-byproduct Supplementation During Late Gestation and Lactation in Landrace Hair Sheep During Different Seasons Managed Under Accelerated Mating on Pasture

Abstract Forage-based production systems are limited by seasonal fluctuations in forage quality and quantity, and may not always meet the nutritional requirements of all stages of production. This study evaluated the use of agro-byproduct (soy hull and corn gluten feed) supplementation to fill increased nutritional demands during late gestation and lactation in Barbados Blackbelly (BB) and St. Croix (STX) hair ewes managed under accelerated mating in a forage-based system. Ewes were bred in March, July, and November in 25-d breeding seasons in two single-sire groups to like breed sires, and subsequently managed as one group. Pregnant ewes (30-36 per season) were allocated balanced by breed, parity and fetal numbers to either soy hull (SH) or soy hull/ corn gluten feed (CG/SH; 50:50 mix) supplementation starting the last trimester. Ewes rotationally grazed or were provided hay on pastures divided into 6 sections (0.13 ha; 3 sections of 5 - 6 ewes per supplement type). Ewes were supplemented at either 0.75% BW (gestation) or 1.5% BW (lactation) as a group. Ewes lambed on pasture and lambs were weaned around 63 d. Data were collected on ewe body weight changes and reproductive performance. Data were analyzed in a model with supplement type, mating season, and breed as main effects, and values are presented as least squares means. Supplement type had no effect on ewe BW daily gain during late gestation or lactation, litter size a birth and weaning, and litter ADG at any stage of production, regardless of breed or mating season. Mating season affected (P < 0.001) late gestation ADG and was highest following July mating (182 g/d), intermediate in March (144 g/d) and lowest in November (101 g/d), but had no effect on lactation ADG. Litter birth weight was higher (P < 0.05) following November (5.4 kg) and July (5.3 kg) than March mating (4.4 kg). Litter weaning weight and pre-weaning ADG was higher (P < 0.05) following November (20.4 kg and 240 g/d) than March mating (16.3 kg and 188 g/d) with July being intermediate (18.4 kg and 221 g/d). Similarly, litter size at birth and weaning was higher (P < 0.05) following November mating (1.87 and 1.69) than in July (1.56 and 1.49) and March (1.42 and 1.31). Body weight tended to be higher in STX than BB prepartum (51.7 vs. 48.2; P < 0.1) and postpartum (45.9 vs.42.4 kg; P < 0.05), but was not different between breeds at weaning. Breed did not affect gestation weight gain, but lactation BW loss was more severe in STX (-71 g/d) than BB (-46 g/d). Findings indicate no differences between supplement types in growth and reproductive performance of landrace hair sheep during different seasons despite the higher crude protein content of the agro-byproduct mix.