Responses to selection for lean tissue growth in Dorset Down sheep
S.J. Nsoso, P.R. Beatson, M.J. Young, C.M. Logan
Animal and Veterinary Sciences Group, Lincoln University,
Canterbury, New Zealand.
Proceedings of the New Zealand Society of Animal Production 1994,
54: 255-260
Responses to selection using a lean tissue growth index were estimated
from performance data of the Lincoln University Dorset Down flock. Data
were available for ewes (n=922) born in the years 1984 - 1991 and rams
(n=816) born in 1984 - 1992. Data were from two closed lines, one control and
the other selected for high lean tissue growth. Initially selection was on the
basis of an index comprising measurements of live weight and fat depth.
Subsequently muscle depth was incorporated into the index. Ewes and rams
born in spring each year were run separately at pasture from weaning (late
summer) onwards. Performance testing was in the following autumn for ewes
and winter for rams. Measurements were live weight and in vivo ultrasonic
fat and muscle depths. Responses were calculated from regression of the
difference between the line means for breeding value against time. Breeding
value estimates were derived by AIREML analyses.
Both sexes exhibited desirable responses in all component traits: rams;
+0.290kg/yr, +0.019mm/yr and -0.013mm/yr and ewes; +0.154kg/yr,
+0.028mm/yr and -0.028mm/yr for live weight, muscle and fat depths
respectively. Increases in muscle depth occurred after it was incorporated
into the selection index.
Keywords: NZSAPAB;
selection response; lean tissue growth; live weight; fat and muscle
depths.
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Last Updated 25-01-1997
