Progress with selection to change age at puberty and
reproductive rate in Angus cattle.
C.A. Morris and J.A. Wilson
AgResearch, Ruakura, Agricultural Research Centre, Private Bag
3123, Hamilton.
Proceedings of the New Zealand Society of Animal Production. 1997,
57: 9-11
Trying to improve beef cow pregnancy rate by genetic selection
within a breed is generally considered to be slow and difficult. In a
novel approach, the present study involves selecting to change age at
puberty in heifers and then exploiting the genetic correlation with
lifetime pregnancy rate. Angus herds were established from a common
foundation population in the early 1980s, and were then selected from
1984 (first calves born in 1985) for reduced age at puberty (AGE-) or
increased age at puberty (AGE+), with a control herd for comparison.
Relative to the AGE+ herd, heifers born in the AGE- herd in 1993 to 1995
were 81 days (=19%) younger at puberty (P<0.001), and their
half-brothers had a 1.8 cm (=6.0%) greater scrotal circumference at 8,
10 and 12 months of age (P<0.001). Corresponding live weights in the
AGE- herd were 18% less at puberty (P<0.001), not significantly
different between herds at birth, weaning or 8 months of age, and 2.4%
higher as yearlings (P<0.05) than in the AGE+ herd. Conception rates for
the 1992 to 1996 matings were 91.4 and 64.6% (P<0.001) for AGE- and AGE+
yearling heifers, but not yet significant at 89.9 and 85.6%,
respectively, for older cows. Restricted maximum likelihood estimates of
heritability for transformed age at puberty and scrotal circumference
(mean of 3 measurements), using all herds and years of data, were
0.27±0.04 and 0.48±0.05, with a genetic correlation of -0.30±0.10.
Phenotypic standard deviations for age at puberty in the AGE- and AGE+
herds were 51 days for each herd. Within-herd heritabilities for age at
puberty were 0.32±0.11 and 0.13±0.14 for the AGE- and AGE+ herds
respectively.
Keywords: NZSAPAB;
cattle; puberty; age; selection; scrotal circumference.
Last Updated 12-09-1998
