Masters Theses

Date of Award

12-1973

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

D.O. Richardson

Committee Members

J.T. Miles, M.J. Montgomery

Abstract

Production and disposal data on 382 Holstein cows, that initiated 924 lactations during a nine year period, were analyzed to determine the effect of selection practices within a closed herd and to evaluate some alternative methods for selecting replacement heifers.

The average annual removal rate for this herd was 34.4 percent» The reasons for removal and percent of the total removals were; low production 48.7 percent; reproduction 16.0 percent; mastitis or udder problems 14.8 percent; disease or injury 8.8 percent; aborted 5.4 per cent; died 5,4 percent, and other reasons 0.9 percent. Cows removed for low production produced 24.2 percent less than the average of the herd.

Most removals for low production came within the first four lactations with involuntary reasons being more prevalent after the fourth lactation. Of the cows removed in the first lactation, 70.3 percent were for voluntary reasons. Cows removed voluntarily consistently produced below their herd mates. Involuntary removals produced more than their average herd mates through the first four lactations, then less in the remaining lactations.

Cows that calved in February and March, the highest production season, produced an average of 2,008 pounds mature equivalent fat corrected milk more than those that calved in August and September which was the lowest period.

The first lactation cows that survived culling produced 883 pounds mature equivalent fat corrected milk more than all herd mates and 396 pounds mature equivalent fat corrected milk more than heifers selected on pedigree merit when only heifers with average or above pedigree merit were used. This data strongly suggests that for the greatest genetic progress it is best to allow all healthy heifers to calve and remove those that do not produce acceptably.

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