Hybrid vigor and lamb production part 2 effects on survival and growth of 1st cross lambs and on wool and body measurements of hogget ewes
Mcguirk, B.J.; Bourke, M.E.; Manwaring, J.M.
Australian Journal of Experimental Agriculture and Animal Husbandry 18(95): 753-763
Drops (5) of Border Leicester (BB), Merino (MM), Border Leicester .times. Merino (BM) and Merino .times. Border Leicester (MB) lambs were compared to estimate hybrid vigor effects on lamb survival and growth, and on the wool and body measurements of ewe hoggets. Hybrid vigor was estimated as the percentage superiority of the crossbreds 1/2(MB + BM) over the average of the purebred 1/2(BB + MM) flocks. Hybrid vigor was observed for lamb survival, with the crossbreds superior by 10% in lambs weaned/lamb born (P < 0.05). The crossbred lambs were heavier at birth (4%) and weaning (6%) and crossbred wether lambs were 11% heavier at slaughter (all P < 0.05). The crossbred ewes were significantly superior to the average of the purebred flocks in both greasy (8%) and clean fleece wt (12%), liveweight (12%) and chest depth (5%) (all P < 0.05). There is no evidence that the crossbreds are superior in any component of wool production/unit area of the skin; fiber length, fiber diameter or follicle density. The breeds and crosses apparently differ in their susceptibility to pneumonia and there may be heterosis for resistance. This siutation gives rise to heterosis for production characters and the heterosis estimates obtained are applicable to first-cross flocks derived from Border Leicester studs which are susceptible to pneumonia. Lamb survival to weaning was higher for purebred Merinos (88%) than for purebred Border Leicesters (73%, P < 0.05). The Border Leicester lambs were heavier at all ages and in all yr, though the magnitude of their superiority varied significantly between yr (P < 0.05). This breed .times. yr interaction was also significant for clean fleece wt, but the average production of the 2 groups was similar over the 5 yr. Variation, measured as the coefficient of variation, was generally lower within the crossbred blocks for those characters where hybrid vigor effects were observed, but these differences were not statistically significant.