Genetically
size-scaled growth and composition
of Dorset and Suffolk Rams
A.M. Oberbauer†, A.M. Arnold‡ and M.L. Thonney§
(Anim. Prod. 59:223-234, 1994) Department of Animal Science, 114 Morrison Hall, Cornell University,
Ithaca, NY 14853-4801, USA
Abstract
Abstract
Thirty-four Dorset Rams and 34 Suffolk rams were slaughtered
in pairs within breed at birth, weaning, at monthly intervals to
420 days and then at bimonthly intervals until 600 days to compare
factors used to estimate mature size and to determine how genetic
size-scaling affects the comparison of body composition between
breeds. At equal empty body weights there were no detectable differences
between the breeds in amounts of water, protein or ash but Dorsets
contained more lipid. Dorset and Suffolk asymptotic values of water
(40 and 61 kg), water-plus-protein-plus-ash (51 and 77 kg), metacarpal
bone length (127 and 147 mm) and metacarpal bone weight (59 and
101 g) were used to estimate mature size. Regardless of the estimator
of mature size, there were no significant differences between breeds
in the degree of maturity of water, protein or ash, with the exception
of small differences in protein for two of the mature size indicators.
Because lipid appeared to accumulate without limit in these sheep,
the mature body was assumed to contain 300 g lipid per kg. Using
this proportion to estimate amount of mature lipid, there was a
higher degree of maturity of lipid for Suffolk than for Dorset
rams at equal degrees of maturity of water, water-plus-protein-plus
ash or metacarpal bone weight. Thus, Dorsets with greater lipid
content at equivalent empty body weights were leaner than Suffolks
when adjusted for mature size. The similarity in water, protein
and ash content among breeds of diverse mature size, when adjusted
for genetic size using a wide variety of mature size estimators,
implies that the genetic size-scaling rules apply within sheep
breeds if any lipid-independent estimator of mature size is used.
Keywords: body composition, growth, sheep, size-scaling.
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