Date of Award:

1984

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Animal, Dairy, and Veterinary Sciences

Advisor/Chair:

James A. Bennett

Abstract

Two biological types of cows, straig htbred Herefords (HxH) and Simmental-Hereford cros ses (SxH), of similar body condition were individually fed over a 10 week period to compare the biological types for maintenance and to determine the influence of milk production potential and of size. Cows were nonlactating and in the last part of the first trimester of pregnancy. During the first 5 weeks of the feeding experiment, one-half of each type was fed 75% of est imated maintenance while the other half was fed 125% of estimated maintenance. During the last 5 weeks of the experiment those fed at 75% of maintenance in the first 5 weeks were now fed 140% of maintenance while those fed 125% of maintenance in the first 5 weeks were now fed 65% of maintenance.

Maintenance requirement was estimated by two methods. The first method, regression of gain or loss on energy intake, showed a higher, but non-significant maintenance requirement for SxH (137.5 vs. 128.3 kcal ME/kg.75/day for SxH and HxH, respectively).

The second method, which involved estimating maintenance as the residual when energy associated with gain or loss in weight was subtracted or added to the total energy intake, gave maintenance values of 117.6 and 145.9 kcal ME/kg.75/day for HxH and SxH cows, respectively.

A comparison of gain in weight for amount of energy consumed, for cows having equal energy intake per unit of metabolic size, indicated that HxH cows used energy more efficiently than SxH cows (P<.20).

The SxH cows were higher in milk production but when the effects of biological type were removed milk production potential was not significant.

Size had a linear, negative effect upon maintenance requirement even though weight was expressed as wkg.75. When the .75 exponent was replaced by either .7, .73, or .78, size was still significant and negative.

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