Ar. Gilmour et al., GENETIC-PARAMETERS FOR ULTRASOUND FAT DEPTH AND EYE MUSCLE MEASUREMENTS IN LIVE POLL DORSET SHEEP, Australian Journal of Agricultural Research, 45(6), 1994, pp. 1281-1291
The study was conducted to estimate heritabilities and genetic correla
tions for liveweight, fat depth at the C site and eye muscle depth, wi
dth and area measured by B mode ultrasound on live young sheep. Record
s on 4338 animals were available for analysis, representing 161 sires
and 79 management/sex groups. The management groups were allocated to
young (5-9 months), medium (10-13 months) and old (14-18 months) data
sets for analysis, representing 89, 82 and 19 sires respectively. The
heritabilities of liveweight, ultrasonic fat depth and ultrasonic eye
muscle measurements were estimated after adjusting for management/sex
group, birth and rearing type, age class of dam and age of the animal.
The heritability estimates for the three age data sets respectively w
ere: for liveweight 0.19+/-0.06, 0.11+/-0.06 and 0.37+/-0.18; for fat
depth 0.01+/-0.03, 0.18+/-0.07 and 0.28+/-0.15; and for eye muscle dep
th 0.15+/-0.05, 0.11+/-0.06 and 0.16+/-0.11. After adjusting for sex/m
anagement group and liveweight within sex (the other factors listed ab
ove being no longer significant), heritability estimates were: for adj
usted fat depth 0.11+/-0.05, 0.33+/-0.09 and 0.29+/-0.16 and for adjus
ted eye muscle depth 0.15+/-0.06, 0.15+/-0.06 and 0.19+/-0.12. The her
itability estimates for eye muscle area, estimated as the area of an e
llipse with dimensions equal to the measured depth and width, were abo
ut 10% lower than for eye muscle depth, but the genetic correlations w
ith depth, in each case were 0.94 or higher. The heritability estimate
s for eye muscle width were less than 0.05 in young and medium age ani
mals and 0.12 to 0.15 in old animals with high genetic correlations wi
th depth which were not different from 1.00. Ultrasound measurements o
f fat depth at the GR site were available on 2065 lambs under 8 months
of age representing 76 sires in 33 groups. The heritability estimates
for fat depth adjusted for liveweight, at the GR and C sites in these
lambs were both 0.10+/-0.05 with the genetic correlation between site
s being 0.76+/-0.19. There is potential for including eye muscle depth
in selection indices to improve leanness. Ultrasound measurement of e
ye muscle width and area will not improve prediction of eye muscle ove
r that attained by measuring eye muscle depth. Predicted responses in
liveweight, fat depth and eye muscle depth for five breeding objective
s for terminal sires, using the appropriate LAMBPLAN selection indices
, are shown and discussed.