Masters Theses

W. L. Bryson

Date of Award

12-1983

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Will T. Butts Jr.

Committee Members

J. W. Holloway, R. A. McLean

Abstract

One hundred thirteen Angus cow-calf pairs (62 mature cows and 25 sires) were individually fed ad libitum over a five year period. Variation in cow size and production potential was comparable to that of Tennessee Agricultural Experiment Station herds. Postweaning, calves were individually fed a complete growing and finishing ration. Unit efficiency (UNEFF) was defined as the ratio of cow TON consumption to calf weight. Prediction equations (Y = b₀ + b₁ (AGE) + b₂ (AGE)²) for weight, fat, postweaning gain, postweaning TON intake and unit efficiency was determined from biweekly weight, fat and feed consumption records. Instantaneous efficiency (INEFF) was the ratio of the rate of TON intake to the rate of gain at a given point (ratio of slopes of tangent lines to each respective equation). The most efficient point (MEP) was determined as the minimum of the equation for UNEFF. Factor analysis was performed to aid in the description of animals. Regression analysis was performed to determine relationships of preweaning cow-calf characteristics to characteristics at selected postweaning endpoints. Preweaning cow-calf characteristics explained appreciable variation in UNEFF, weight, and age, above that explained by year and sex, at MEP, 400 kg weight (WT400), 14 mm fat (FAT14), 207 days postweaning (207DAYS) or at an INEFF of nine kg TDN/kg gain (INEFF9). Cow weight at the previous weaning was negatively related (P<.05) to UNEFF at INEFF9 and to postweaning gain at WT400. Cow weight change from previous to current weaning was positively (P<.05) related to age, postweaning TON and INEFF at MEP. Cow fat positively affected age, fat and postweaning days at MEP (P<.05). Calf weight and postweaning gain, when evaluated at FAT14, were negatively affected (P<.05) by cow fat at previous weaning. Age at all endpoints was positively affected by weaning age (P<.001). Also younger calves at weaning gained more to WT400 (P<.001). Thinner calves at weaning were higher in INEFF at FAT14, but were lower in INEFF at MEP (P<.05). UNEFF at all endpoints was positively related to weaning efficiency (P<.001). Weaning efficiency also had a positive effect on gain at WT400 (P<.001) and INEFF at MEP (P< .05). Weaning efficiency showed a negative effect (P<.05) on instantaneous rate of gain (INGAIN) when evaluated at MEP, WT400 or 207DAYS. The variables not affected by sex were TON intake at 207DAYS; INEFF and postweaning gain at WT400; INEFF and INGAIN at FAT14; age, postweaning TON intake and days postweaning at MEP; and INGAIN, fat, age and postweaning days at INEFF9. Calf weaning weight had a positive effect on UNEFF, weight, postweaning TON, instantaneous intake and INEFF at MEP (P<.05). Calf weaning weight also had a positive effect on UNEFF, weight, postweaning TON and instantaneous intake at FAT14 (P<.05). Weaning age was a positive effect (P<.001) upon UNEFF, weight, postweaning TDN, fat and instantaneous rate of intake at 207DAYS. AT INEFF9, weaning weight was positively correlated with UNEFF, weight, instantaneous TDN intake and INGAIN and was negatively correlated with postweaning days (P< .05). At WT400, calf weaning weight had a negative (P <.05) effect on age, postweaning days, postweaning TDN, fat and INEFF and had positive effects on weight, instantaneous rate of intake and INGAIN. Preweaning cow-calf characteristics were relatively unimportant in explaining variation in all calf characteristics studied unless evaluated at 400 kg weight. This is interpreted to be attributed to relationship of these preweaning characteristics to physiological age. Preweaning characteristics of cow-calf pairs were importantly related across all endpoints only to calf age, weight and unit efficiency. These relationships were thought to reflect the part-whole aspects of these variables from weaning to postweaning. These results suggest that little biological antagonism exists between pre- and postweaning factors related to feed efficiency. Increased unit efficiency at weaning is favorably associated with unit efficiency at all endpoints studied and is either favorably associated with calf instantaneous efficiency evaluated at the most efficient point or is independent of that measure of efficiency at other endpoints. Preweaning pair characteristics were related to slaughter age and weight at all endpoints but were largely independent of level of calf fatness. Variation in preweaning characteristics and relationships between pre- and postweaning characteristics reported in this study provide producers an opportunity to select particular kinds of animals to achieve specific goals in specific production and economic situations.

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