Abstract
Pasture-based sheep production may require supplementation during periods of reduced forage quality and quantity, and periods of high nutritional demands. This experiment compared soy hull to a more traditional corn-based supplement for hair sheep ewes managed in a pasture-based accelerated mating system. Growth performance and fitness of the lambs was evaluated. Ewes (Barbados Blackbelly and St. Croix; 30 -36 per season) 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 corn/soybean meal (CS) or soy hull (SH) supplementation starting the last trimester. Ewes were supplemented at either 0.75% BW (gestation) or 1.5% BW (lactation). 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). Lambs were born on pasture, had access to the supplement provided to their dams and were weaned around 9 wk. Lamb birth and weaning weights were recorded, and fecal egg counts (FEC), packed cell volume (PCV), and body condition (BC) were determined at weaning. Data (n = 175) were analyzed in a model with supplement type, mating season, breed, sex, and birth type as main effects. FEC were log-transformed before analysis (means reported). Lambs with access to the CS tended (P < 0.1) to have a higher 60-d adjusted weaning weight (11.8 vs. 11.5 kg), pre-weaning ADG (148 vs. 135 g/d), and BC (1.82 vs. 1.64) compared to SH lambs. There was no effect of supplement type on FEC and PCV. Mating season had a significant P < 0.01) effect on lamb weaning weight (April: 12.4 kg; August: 11.4 kg; December: 10.5 kg) and pre-weaning growth and ADG was higher (P < 0.001) in April-born (155 g/d) compared to December-born lambs (126 g/d), with August-born lambs being intermediate (144 g/d). There was a supplement type x season interaction (P < 0.05) for weaning weight and ADG with lower growth performance in SH-supplemented lambs in July, and increased growth in CS-supplemented lambs in November. Lamb survival to weaning tended (P = 0.08) to be higher in SH-supplemented (92.1%) than CS-supplemented (83.7%) lambs. There was no effect of season on BC, FEC, and PCV. St. Croix lambs had higher (P < 0.05) birth and weaning weights, but not pre-weaning ADG than Barbados Blackbelly lambs, and lower PCV (P < 0.05). There was no effect of breed on FEC. The season by supplement type interaction suggested an influence of forage environment on the supplementation response. Soy hull supplementation caused a nominal reduction in pre-weaning growth of lambs, but improved in lamb survival and presents a viable supplement in a forage-based production system.