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Selection practices in dairy herds. 1. First lactation performance and survival to the second lactation

Published online by Cambridge University Press:  02 September 2010

C. J. M. Hinks
C. J. M. Hinks
Affiliation:
Institute of Animal Genetics, Edinburgh†
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Extract

1. The relationship between first lactation performance and the ability of individual animals to survive to the second lactation has been examined in Friesian and Ayrshire populations in an attempt to isolate the main determinants of survival, and to rationalise an apparently complicated selection procedure.

2. Low milk yield was the most important single cause of culling in the first lactation, though the two breeds differed considerably in the relative importance of milk yield in the selection programme. Natural wastage, caused by factors beyond the control of the farmer, accounted for the disposal of 5·7% of the population during the first lactation. Selection for butterfat was marginal in both populations, and could only be detected at extreme butterfat percentages, where high butterfat tended to compensate for a poor milk yield, and low butterfat to confirm a decision to cull an average yielding animal. Survival was not significantly affected either by the size of the herd or by the age at calving.

3. The proportion culled, and the intensity and effectiveness of selection for milk yield, were inversely related to the level of herd performance, and were greater in summer calving animals than in winter calvers.

4. The analysis indicated that selection for milk yield in different environments could be adequately described in terms of the Normal Curve. Yield-survival curves were computed and compared for groups of animals in different herd and calving season environments. When milk yield was expressed in terms of the deviation from the herd-year average, it was found that summer calvers, and animals in low yielding herds, had to demonstrate a productive capacity of far greater individual merit, if their chances of survival were to match those of their winter calving herdmates, and those of their contemporaries in higher yielding herds. When milk yield was expressed in absolute terms the survival of individual animals of similar yield was comparable in all herd and season environments. It was concluded that all the herds included in the analysis had been subject to the same absolute standards of milk yield in the selection of first calvers.

Type
Research Article
Information
Animal Production , Volume 8 , Issue 3 , October 1966 , pp. 467 - 480
Copyright
Copyright © British Society of Animal Science 1966

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References

REFERENCES

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