At Mount Derrimut Field Station from 1982 to 1985, growth and body
composition was studied in
three groups of wethers from the same flock. A control group (C) and a
restricted group (R) were
housed from the age of 1 day until slaughtered. The first slaughter was at
the age of c. 1 year (reported
elsewhere) and the second at the age of c. 3 years. Apart from the
first 36 days, when group R was
fed a severely restricted ration, both groups were fed a high quality diet
ad libitum throughout the
experiment. At the end of the second year, a group of 2-year-old wethers (G)
was introduced, to
compare the growth of these sheep with those in groups C and R. Group G sheep
were reared on their
dams, kept as grazing animals and killed at the second slaughter.
At the age of c. 3 years there was no significant difference
between groups C and R for mean fleece-free body weights, but the sheep in
group G were significantly lighter (P<0·01) in spite of reaching
mature size for grazing sheep in the general flock.
After the age of 7 months there was no significant difference between
groups C and R in rate of
wool production. Rate of wool production in group G sheep was not significantly
different from that
of sheep in the other groups except during the last 6 months, when they produced
significantly less wool (P<0·05).
Regression analyses for surface and X-ray measurements against fleece-free
body weight
(independent variable) showed no differences between groups C and R, except
for width of
metacarpal (X-ray measurement). In this case, the regression coefficients
were different (P<0·01)
but, at slaughter, actual bone measurements were the same. Both X-ray
measurements and those at
dissection showed that the metacarpals of group G were significantly
(P<0·05) longer and narrower,
and had a narrower cortex, than those in the other two groups
(P<0·05).
There were no significant differences between groups C and R in mean
weight and chemical
composition of the parts and tissues examined; however, the carcass fat content
of sheep in group G
was significantly less (P<0·01) than in the other two groups.
The sheep in group G had higher
weights (P<0·01) for the brain, the digestive tract
(DT), kidneys and liver than those in groups C and R.
Cell size in the semitendinosus muscle, as indicated by the
protein[ratio ]DNA ratio, increased (P<0·01)
between the first and second slaughters. There were no differences between
groups in protein[ratio ]DNA
ratios, but the DNA and protein contents were significantly higher
(P<0·05) in the kidneys and liver
in group G than in the other groups. Although the weights of the semitendinosus
muscle were heavier
(P<0·01) in groups C and R than in group G, on a
fat-free basis, there were no significant differences
between treatments in muscle weight or in DNA and protein contents.
It is concluded that sheep will make a complete recovery after a severe
nutritional check in early
post-natal life if given the opportunity to do so. Even though large
differences in body weight may
develop between sheep, this appears to have little effect on mature
skeletal dimensions. However, at
maturity, with grazing sheep that grow relatively slowly, the metacarpals
are likely to be narrower and
longer than those of the same genotype fed to grow faster. Even with sheep fed
ad libitum throughout
life, the use of X-ray and surface measurements in young sheep at a
particular body weight are
unlikely to be useful for the accurate prediction of mature body weight.
