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Fertility in a tropical beef herd divergently selected for pregnancy rate

Published online by Cambridge University Press:  02 September 2010

D. J. S. Hetzel ,
M. J. Mackinnon ,
R. Dixon  and
K. W. Entwistle
D. J. S. Hetzel
Affiliation:
CSIRO, Division of Tropical Animal Production, Tropical Cattle Research Centre, North Rockhampton, Queensland 4702, Australia
M. J. Mackinnon
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
K. W. Entwistle
Affiliation:
School of Tropical Veterinary Science, James Cook University of North Queensland, Townsville, Queensland 4811, Australia
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Abstract

Selection on the basis of estimated breeding value for cow fertility was successful in establishing two distinct lines of high (H) and low (L) fertility in a herd of Droughtmaster (Brahman × Shorthorn) cattle. The average difference in pregnancy rates over 3 years between the H and L line was 12% (P < 0·01) in the selected cows. In lactating cows this difference was 17% indicating that lactational anoestrus was an important component of the line difference in fertility. The total calf losses between confirmed pregnancy and weaning were 17%, but there were no line differences. Cow mortalities were 5% higher (P < 0·01) in pregnant cows than in empty cows but were similar in the H and L 'lines.

H cows were proportionately 0·06 lighter in body weight (P < 0·01) at mating and 0·075 lighter (P < 0·01) at weaning than L cows. Much of this difference was due to the greater number of calves carried and weaned by H cows during their lifetime. Smaller lactation effects on weight gains and weight losses in H cows indicated that these cows were less sensitive in terms of weight gain to seasonal fluctuations in nutrition. H cows conceived earlier than L cows in 2 out of the 3 years and reared calves which were proportionately 0·04 lighter at weaning (P < 0·01). It is suggested that lower milk production in H cows leading to shorter periods of lactational anoestrous, combined with lower sensitivity to nutritional stress, was responsible for their higher fertility.

Type
Research Article
Information
Animal Production , Volume 49 , Issue 1 , August 1989 , pp. 73 - 81
Copyright
Copyright © British Society of Animal Science 1989

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References

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