FACTORS INFLUENCING THE GROWTH OF LAMBS REARED ARTIFICIALLY OR WITH THEIR DAMS

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Abstract
Over a 3-yr period, weights of 236 lambs reared artificially with liquid plus solid diet from 2 to 70 days and 298 lambs creep-fed a solid diet and reared with their dams from birth to 70 days were recorded at birth, 35, 70 and 140 days of age. Included were 400 lambs of the Suffolk (SU) and Shropshire (SH) breeds and their reciprocal crosses and 134 lambs of the Ottawa (MM) synthetic strain. There were significant interactions of rearing system with year (P < 0.01) in growth rate up to 140 days of age, and with breed of lamb (P < 0.01), sex (P < 0.05) and type of birth (P < 0.01) up to 70 days. Ram lambs gained more than ewe lambs, but the difference was less in artificial rearing. Singles gained more (P < 0.01) than twins up to 70 days when reared with their dams, but not when reared artificially. Significant (P < 0.01) age of dam effects on body weight persisted up to 70 days for lambs reared artificially and up to 140 days for lambs reared with their dams. The overall mean 140-day weights did not differ significantly in the two systems. Breed means and standard errors of 140-day wt for lambs reared artificially and for lambs reared with their dams were, respectively: MM, 29.7 ± 1.08 and 29.7 ± 0.96 kg; SU, 29.9 ± 1.08 and 32.7 ± 0.95 kg; SH, 24.1 ± 1.31 and 26.2 ± 1.14 kg; SU (sire) × SH (dam), 31.0 ± 1.30 and 30.7 ± 1.08 kg; and SH × SU, 28.9 ± 1.20 and 32.8 ± 1.03 kg.

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