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Genetic Correlation between Type and Production in Jersey Cattle¹

Iowa State College, Ames³

ABSTRACT

The correlation between transmitting ability for type and transmitting ability for production was estimated as 0.18 from 2,786 daughter-dam pairs in the Jersey breed. The data came from 226 herds which had been on HIR test for at least 4 of the 5 yr. 1943 to 1947, inclusive. Additively genetic variation constituted about 18 per cent of the intra-herd and intra-year variance in single records of fat production and 14 per cent of the intra-herd differences in official type ratings.

Selection on the basis of type alone should therefore automatically bring about some genetic improvement in production. However, selection on type alone would require about 6 to 10 generations to obtain the improvement that selection on the basis of production would obtain in only one generation. Postponing selection until the daughter has at least one record of production will increase the genetic gain by 25 to 70 per cent, depending on the relative economic values of type and production.

The fraction of the intra-herd variance in average production (average of two records per cow) that could be attributed to yearly changes in the general environment of that herd was only 4.1 per cent. Such yearly changes are only minor obstacles to accuracy in selections. The yearly effects on production were largely eliminated by using the average of all records available on the cows studied.

Two selection indexes were developed for type and production from the estimates of the necessary parameters observed in this study. One of these gives type one-third as much attention as production, while the other gives both characters equal attention. Only information from the phenotypes of the cow and her dam were considered in constructing the indexes. Several of the combinations of information on the cow and her dam were found to yield progress about half as fast (R_IA is about 0.5) as if the exact Mendelian genotype of the cow were known.

¹ Journal paper no. J-1335 of the Iowa Agricultural Experiment Station, Ames. Project no. 1053.

² Present address: Associate Dairy Husbandman, University of Idaho.

³ The American Jersey Cattle Club permitted the use of its data and also helped meet the costs of the computations.

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