New Zealand Journal of Agricultural Research abstracts
Patterns of change with growth for muscularity and other composition
characteristics of Southdown rams selected for high and low backfat depth
A. Y. ABDULLAH
R. W. PURCHAS
Department of Animal Science
Massey University
Private Bag 11222
Palmerston North, New Zealand
A. S. DAVIES
Department of Physiology and Anatomy
Massey University
Private Bag 11222
Palmerston North, New Zealand
Abstract Male Southdown sheep ranging in age from birth to
near maturity (c. 28 mo) from genetic lines selected for about five generations
for increased (n = 40) and decreased (n = 40) weight-adjusted
ultrasonic backfat depth were used to investigate patterns of change in
muscularity and other composition characteristics. Measures of muscularity in
terms of muscle depth relative to bone length were greater for the high-backfat
line in anatomical areas around or beside the femur, tibia, total pelvic limb,
humerus, and scapula, but not the radius/ulna. Levels of muscularity increased
at a decreasing rate with increasing carcass weight from about 1 to 36 kg in
all areas. Where there was a genetic line effect on muscularity, this tended to
be greater at higher carcass weights, with minimal differences at birth. Muscle
to bone ratios corresponding to these measures of muscularity showed similar
patterns of change and line differences. Leg bone weight was higher for the
low-backfat line; for the same femur length, a number of femur dimensions were
greater for that line. Carcass length at a set weight was greater for the
low-backfat line, and the allometric growth ratio (AGR) for length declined
with increasing carcass weight. Greater measures of fatness for the
high-backfat line only became apparent at carcass weights above about 10 kg and
AGRs for measures of fatness increased with increasing carcass weight. Some
non-carcass offal components (liver, spleen, heart) were heavier in rams of the
low-backfat line at the same carcass weight, and AGRs for liver and spleen
decreased with increasing carcass weight. It is concluded that, in addition to
decreases in fatness, selection for lower backfat depths in these Southdown
rams has led to a number of other undesirable composition changes including
lower levels of muscularity and muscle to bone ratios, changes in the shape of
the femur, and greater weights of some non-carcass components. Generally these
changes were more apparent at higher liveweights.
Keywords backfat selection lines; muscularity; sheep growth;
allometric growth; bone growth; Southdown rams
New Zealand Journal of Agricultural Research, 1998, Vol. 41: 367-376
0028-8233/98/4103-0367 $7.00/0 (c) The Royal Society of New Zealand
1998
PDF file of entire paper: medium quality (803K); (scanned from paper original: notes about this process)
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