PSXII-29 - Evaluation of Barbados Blackbelly and St. Croix sheep under accelerated lambing using purebred and terminal sire mating: Lamb survival and body weight

Objectives were to evaluate lamb survival and body weight (BW) under an accelerated, pasture-lambing system. Lambs were born to Barbados Blackbelly (BB) or St. Croix dams (SC) mated within breed (purebred) or to Dorset (terminal) in single sire mating groups. Lambs were born in April (2013 and 2015), December (2013 and 2015), and August (2014 and 2016) and weaned at 9 weeks of age. Traits considered were BW at birth (BW₀; n = 959), 65-d adjusted weaning BW (BW₆₅; n = 788), and survival to weaning (n = 959). Data were analyzed with fixed effects of dam age, sex, birth type, dam breed (BB vs SC), dam mating system (purebred vs terminal), birth month-year, and significant two-way interactions and a random dam effect. Dam breed did not impact BW₆₅ (P = 0.09). While BW₀ was greater for lambs born to SC than BB dams (3.44 vs 3.23 kg; P < 0.01), survival to weaning was greater for lambs born to BB than SC dams (0.93 vs. 0.87; P = 0.02). The dam mating system x birth month-year interaction was significant for both BW traits (P ≤ 0.01). Within birth month-year, BW₀ was 18 to 24% greater and BW₆₅ was 12 to 24% greater for terminal than purebred lambs (P < 0.01). However, BW₀ differences between dam mating systems were greatest for August born lambs whereas BW₆₅ differences were greatest for April born lambs. Lamb survival was not affected by dam mating system or birth month-year (P ≥ 0.27). Using a terminal sire improved BW without affecting survival of lambs reared by landrace hair sheep dams, making this a viable management tool to increase productivity of forage-based production systems.