The growth of 26 castrated ram lambs was severely restricted for the first 5 weeks of post-natal life. Subsequently, these lambs (group R) were fed ad libitum on the same high quality diets as fed to a control group of 26 similar lambs (group C) from birth.
At regular intervals lambs were weighed, X-rayed and surface measurements were aken. At the age of 12–14 months, covering the body-weight range of 63–83 kg, ten animals from each group were slaughtered for dissection and measurement. These data were used to compare the skeletal growth of the two groups of animals. Measurements of skeletal dimensions by dissection were compared with measurements obtained by surface and radiographic techniques. After slaughter, the brain, kidneys, liver, the left semitendinosus and gastrocnemius muscles from each lamb were used for the following analyses: dry matter, ash, fat, protein, DNA and RNA contents.
At the end of the period of feed restriction, there was a mean body-weight difference between groups of 9·2 kg (63%).This represented a weight for age difference of 36 days, which was reduced to 29 days at the conclusion of the experiment, restricted animals not having fully recovered from the period of underfeeding.
Clean wool production per day was significantly (P < 0·05) depressed by the restricted feeding, lambs in group C producing 11·07 g/day during the first shearing interval compared with 10·07 g/day from group R lambs. There was no difference between groups in clean wool produced during the second shearing interval.
Restricted feeding caused a reduction in the rate of bone growth but, during subsequent regrowth (apart from minor exceptions), it did not disrupt the relationship of skeletal dimensions to fleece-free body weight (FFBW). Surface measurements showed that during recovery, group R animals were significantly narrower (P < 0·05) at the hips and wider (P < 0·05) at the shoulders than group C animals. The results obtained from the radiographs for length of foreleg were similar to those obtained from surface measurements. Metacarpal width (measured at two sites) and weight were significantly greater in group R than in group C animals. With the exception of width at hips and although not statistically significant (P > 0·05), the skeletal measurements of group R were slightly greater than those of group C animals. This may have been due to the slightly greater age of group R at slaughter and to an effect of restricted feeding.
There was no significant difference between groups R and C in the DNA content of the tissues investigated. Neither was there any difference between the groups in cell size as indicated by the protein: DNA and tissue weight: DNA ratios. Even though hyperplasia and hypertrophy were slowed by the period of restricted feeding, this effect was transient, full recovery apparently occurring as indicated by tissue weights and composition at the time of slaughter. The RNA and the protein contents of the tissues were similar in both groups. In addition, the similarity of the RNA:DNA ratios suggests that tissues in each group possessed the same capacity to synthesize protein.
In practical terms, the recovery of group R was associated with a time lag in reaching any particular body weight and a loss of wool production. Both of these consequences are of economic importance. At the time the experiment ended, no skeletal stunting was evident in these sheep and, apparently, they had recovered in terms of cellular growth.