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Correlated responses to selection for cow fertility in a tropical beef herd

Published online by Cambridge University Press:  02 September 2010

M. J. Mackinnon ,
D. J. S. Hetzel ,
N. J. Corbet ,
R. P. Bryan  and
R. Dixon
M. J. Mackinnon
Affiliation:
CSIRO, Division of Tropical Animal Production, Tropical Cattle Research Centre, North Rockhampton, Queensland 4702, Australia
D. J. S. Hetzel
Affiliation:
CSIRO, Division of Tropical Animal Production, Tropical Cattle Research Centre, North Rockhampton, Queensland 4702, Australia
N. J. Corbet
Affiliation:
CSIRO, Division of Tropical Animal Production, Tropical Cattle Research Centre, North Rockhampton, Queensland 4702, Australia
R. P. Bryan
Affiliation:
CSIRO, Division of Tropical Animal Production, Tropical Cattle Research Centre, North Rockhampton, Queensland 4702, Australia
R. Dixon
Affiliation:
CSIRO, Division of Tropical Crops and Pastures, Davies Laboratory, Townsville, Queensland 4814, Australia
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Abstract

Correlated responses to selection in a tropical beef herd for high (H) and low (L) estimated breeding value for pregnancy rate were measured over three calf crops. The H line calves were proportionately 0·04 lighter at weaning but during the ensuing dry season they lost less weight than L line animals, so that between the ages of 12 and 18 months there were no significant line differences in live weight. It was concluded that selection for cow fertility had not directly altered the progeny's growth rate. Tick resistance and heat tolerance also did not differ between the lines. However, resistance to worms was lower (P < 0·05) in the H line indicating genetic antagonism between cow fertility and worm resistance. Scrotal circumference and scrotal circumference adjusted for live weight were significantly higher in H line bulls between 9 and 18 months of age. Pregnancy rates of heifers in the H line were 0·12 higher than in the L line despite similar average live weights at mating. It is suggested that accelerated sexual maturity in both heifers and bulls has occurred as a result of selection for lifelong cow fertility.

Keywords

cattlefertilityselectiontropics
Type
Research Article
Information
Animal Production , Volume 50 , Issue 3 , June 1990 , pp. 417 - 424
Copyright
Copyright © British Society of Animal Science 1990

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