Abstract:
The growth of Merino lambs was retarded under field conditions at two stages during the first year of life, and for the 6 years following the removal of growth restrictions the residual effects of the treatments were measured in terms of body weight, body size, wool production, teeth development and wear, and mortalities.Growth during the recovery period differed according to previous treatment. The effects of retarded growth during the first 6 months of life (pre-weaning treatment) persisted for 56 months whereas undernutrition during the second 6 months of life (post-weaning treatment) lasted for only 11 months. Each effect was independent and additive. Generous feeding during the post-weaning period produced transitory benefits but did not compensate for poor nutrition during the suckling period. All groups ultimately attained normal adult weight and stature.Pre-weaning undernutrition had as its sequel a significant reduction in clean wool production (total 620 g) during the first 23 months of the recovery period; no residual effect of post-weaning undernutrition was detectable during the early part of the recovery period. However, comparisons of the total clean wool production of the treatment groups for the 6-year recovery period provided no evidence of significant differences other than those due to sex. Wethers produced 13% (2.74 kg) more clean wool than ewes and were 15% heavier in body weight. There were no differences between the groups in respect of mortalities. Retarded growth delayed the eruption of the permanent incisors by up to 16 weeks. Teeth losses were similar in all groups.