Post-weaning Growth and Carcass Traits of St. Croix White and Dorper X St. Croix White Lambs Grazing Pasture During the Dry and Wet Seasons in the U.S. Virgin Islands

This study was conducted to evaluate post-weaning growth, carcass traits and parasite burdens St. Croix White (STX) and Dorper X St. Croix White (DRP) lambs grazing guinea grass pastures during the wet and dry seasons. Lambs (77 d of age) were placed in guinea grass pastures (0.5 ha) in a rotational grazing system. Fecal egg count (FEC), packed cell volume (PCV) and BW were measured weekly. Lambs were slaughtered at a BW of 30 kg. Carcass weight, fat thickness, rib eye area (REA), KPH and leg circumference were measured. Data were analyzed by SAS procedures. Total rainfall was 647.7 mm and 1495.3 mm for the dry and wet seasons, respectively. Forage availability was 432.5 ± 64.6 kg DM/ha and 1051.0 ± 261.9 kg DM/ha during the dry and wet seasons, respectively. The DRP lambs reached target weight sooner (P < 0.0008) than STX lambs (178.2 ± 6.3 d vs. 210.9 ± 6.7 d, respectively). Average daily gain was higher (P < 0.0002) for DRP than for STX lambs (90.3 ± 1.9 g/d vs. 79.1 ± 2.0 g/d, respectively). Carcass weight was not different (P > 0.10) between breed type (13.5 ± 0.1 kg). The REA of DRP lambs was greater (P < 0.01) than that of STX lambs (9.36 ± 0.19 cm2 vs. 8.63 ± 0.21 cm2, respectively). Fat thickness was greater (P < 0.02) in DRP than in STX lambs (1.92 ± 0.10 mm vs. 1.57 ± 0.10 mm, respectively). Leg circumference was larger (P < 0.03) for DRP than for STX lambs (38.2 ± 0.3 cm vs. 37.3 ± 0.3 cm, respectively). There was no difference (P > 0.10) between DRP and STX lambs in FEC or PCV. Dorper-sired lambs reared under an extensive management system will reach market weight sooner than St. Croix White lambs and can tolerate parasite burdens similar to those found in the indigenous hair sheep in the U.S. Virgin Islands.