Undernutrition of the Merino sheep and its sequelae. IV. Herbage consumption and utilization of feed for wool production followint growth restrictions imposed at two stages of early post-natal life in a Mediterranean environment

Abstract

Merino lambs grazing sown pastures in the Mediterranean type environment of southern Australia were subjected to contrasting growth conditions (restricted or continuous) during two periods of early life (birth to 6 months of age and 6–12 months). Thereafter all groups received equal nutritional opportunity and the sequelae to these periods of retarded growth were examined in terms of herbage intake, utilization of feed for wool production, and body weight. During the 28-month recovery period those sheep which received a growth handicap in the first 6 months of life (pre-weaning treatment) did not reduce the weight margin of 6.6 kg held by their previously better-fed mates. They consumed significantly less herbage on an absolute basis, but after adjustment for differences in metabolic size (W0.75) the feed consumption of the two groups was similar. By contrast, sheep which were subjected to growth restrictions during the second 6 months of life (post-weaning treatment) rapidly reduced the weight advantage of 8.1 kg (P < 0.01) held by their well-fed companions at the beginning of the recovery period. This capacity to compensate for the effects of previous undernutrition was associated with a significantly greater feed intake/liveweight0.75 ratio. The effects of pre-weaning and post-weaning nutrition on body weight, feed intake, and wool production were independent and additive, no interactions being observed. Groups subjected to a growth restriction during early post-natal life produced significantly less wool during the first shearing following rehabilitation, but this effect was not sustained. Undernutrition during early life did not impair the efficiency of conversion of feed to wool; differences in wool production were almost wholly due to differences in intake. Wool growth appeared to be less sensitive than body weight to the after-effects of periods of undernutrition in early life.