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Journal of Dairy Science Vol. 57 No. 8 884-888
© 1974 by American Dairy Science Association ®
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Lactation Records of Jersey Cattle in Pennsylvania: Season of Calving, Phenotypic Trend, Heritability, and Genetic Trend1

R. N. Deb2,4, J. L. Gobble2, G. L. Hargrove3 and H. W. Thoele3

The Pennsylvania State University, University Park 16802

ABSTRACT

Lactation records of Jersey cows calving from August, 1961, to November, 1969, in Pennsylvania Dairy Herd Improvement Associations were standardized to 305-day, mature equivalent.

Lactation yield increased for cows that calved in late fall and winter compared to those that calved during summer. Cows in first lactation differed little from all cows in month of calving with respect to (1) high frequency of calving (August to November) and (2) high lactation yield (November through March). The phenotypic increase in milk yield for both first-lactation cows and all cows was 36 kg per year, an annual increase of .9% of the mature equivalent mean milk yield. Only one-half was genetic, suggesting improvement in management and nutrition. The phenotypic trend for fat yield was 1 kg per year with no genetic change. Percentage of fat declined .02% per year.

Heritabilities by intraclass correlations among paternal half-sisters from 7,667 first, 6,258 second, and 4,799 third lactations were .40, .27, and .23 for deviation of milk from herdmates; .31, .19, and .17 for deviation of fat from herdmates; and .67, .65, and .67 for percentage of fat. The decline of heritabilities of yield traits may be from selection (culling) after first lactation.

FOOTNOTES

1 Authorized for publication November 26, 1973 as Paper No. 4585 in the Journal Series of the Pennsylvania Agricultural Experiment Station.

2 Department of Animal Science.

3 Department of Dairy Science.

4 Present address: Nagpur Veterinary College, JP. O. Nagpur, Maharastra, India.






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