Doctoral Dissertations

Date of Award

12-1981

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

Will T. Butts

Committee Members

J.W. Holloway, J.B. McLaren, J.W. Philpot, D.O. Richardson

Abstract

Mature Angus and Hereford cows raising straightbred and reciprocal cross calves were individually fed during their lactations. A total of 92 preweaning lactations and 66 postweaning growth curves were observed. Cows were offered, ad libitum, a diet of grass silage and alfalfa pellets were added as an energy source when needed. Calves were creep fed alfalfa pellets from approximately 80 days of age until weaning. Following weaning calves were individually fed a complete growing and finishing ration until the calves were slaughtered at their maximum efficiency point (MEP). Unit TDN was the sum of cow and calf TDN. Cow-calf unit weaning efficiency was calculated as the ratio of unit TDN to calf weaning weight. Cow-calf unit efficiency, calf age and calf weight were determined for endpoints at 12 mm fat and at MEP. Calf fat was determined at MEP. Postweaning efficiency, postweaning ADG and daily postweaning TDN were determined from weaning to 12 mm fat and MEP, respectively. Angus cow units were more efficient than were Hereford cow units (P<.001) but the effect was reduced when the covariates, milk production and calf weaning weight were added to the basic model. Crossbred calves were slightly heavier (P<.10) at weaning than straightbreds, but because of their higher calf TDN intake, they could not be declared more (P<.10) efficient. Calf weaning weight accounted for about 51 percent of the variation in cow-calf unit efficiency. Calves with improved efficiencies at weaning consumed (P<.001) more daily postweaning TDN. Younger calves were associated (P<.10) with improved postweaning ADG. When adjusted for calf weaning age crossbreds were heavier (P<.05) than straightbreds. Calves of Hereford sires were more efficient (P .01) than calves of Angus sires. Calf weight, at each respective endpoint, adjusted for calf weaning age, increased (P<.05) as cow-calf unit efficiency improved. Units with younger calves at each endpoint tended to be more efficient (P<.10) than units with older calves. Units with smaller cows were more efficient (P<.05) at MEP and (P<.10) at 12 mm fat than were units with larger cows.

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