Doctoral Dissertations

Date of Award

8-1984

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

J.B. McLaren

Committee Members

Robert R. Rhrode, Monty J. Montgomery, John W. Philpot

Abstract

A total of 477 Holstein cows, with data on 1278 lactations, and 823 conformation classifications were used to study the effects of single-trait and multiple-trait sire selection on production and type classification traits.

The production traits studied were mature equivalent milk yield, mature equivalent fat-corrected milk yield, and mature equivalent butterfat yield. The type classification variables studied were total score, and the major breakdown scores, general appearance, dairy character, mammary score, and body capacity. Sires utilized in the mating plan were selected on the basis of either predicted differences for fat-corrected milk (production bulls) or a selection index composed of the predicted difference for fat-corrected milk and mammary scores (merit bulls).

Preliminary analyses of variance showed that the effects of month-fresh, line-year, sire, and lactation number (when applicable) were important in the analyses of both the production and type data.

Upon adjusting for relationships between sires using Henderson's BLUP procedures, analyses were performed again, and the estimates for line-year were regressed over time to establish genetic trends.

The results of the study indicated a positive trend from 1967 to 1982 in production traits, with daughters of the production bulls consistently producing at higher levels of milk and fat than daughters of the merit bulls. When all lactations were included in an analysis, the estimated difference between the lines was less than that estimated by an analysis of first lactation records only. However, the direction of the difference remained the same.

Estimate of type classification traits showed a negative trend over time, with daughters of the merit group consistently scoring higher than daughters of the producing group. There were little differences In the results when the analysis Included ratings made of first and second lactation cows or ratings at all ages.

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