Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Animal Science

Major Professor

W.T. Butts Jr.

Committee Members

D.O. Richardson, R.A. McLean, S.L. Hansard, & J.A. Corrick


Angus cow-calf pairs were individually fed over a five-year period. Data from 62 mature cows and 114 calves were obtained. Cows varied in initial weight and production potential. Cows were fed grass silage, ad libitum, throughout gestation and lactation. Calves were fed a complete finishing and growing ration post weaning. Efficiency of cow-calf units was defined as the ratio of the yearly TDN intake of the cow plus the pre-and post weaning TDN intake of the calves. Second-order polynomials were fitted through the biweekly efficiency ratios for individual calves and solved to determine the most efficient point. This efficiency was also calculated for two constant fat thicknesses and evaluated. The TDN efficiency for three carcass components: separable muscle, protein, and energy were also determined.

At weaning, year and initial cow weight influenced cow annual TDN intake and cow-calf unit intake. Year, sex of calf, and initial cow weight affected weaning TDN efficiency. Calf age and weight at weaning positively influenced weaning TDN efficiency, in the pressure of initial cow weight.

Postweaning, a 100-unit increase in initial cow weight was associated with an average 2-unit increase in TDN consumption. Unit efficiency was positively influenced postweaning by initial cow weight, indicating that lighter cows were slightly more efficient than heavier cows. The average ages for the slaughter calves at 8mm, 12mm, and the most efficient point was 394, 440, and 462 days. Older and/or heavier calves at weaning were associated with improved unit efficiency.

The most efficient point of the carcass components of separable muscle, protein, and energy was 478, 429, and 505 days of age, respectively. Corresponding 12th rib fat estimates for carcass muscle, protein, and energy at the most efficient point were 17,11, and 20mm, respectively. The average product yield at the most efficient point was 147 kg carcass muscle, 34 kg protein, and 1146 Mcal energy. Analysis revealed that heavier weaning weights would increase the yield of carcass muscle, protein, and energy at the most efficient point. More efficient carcass component production was associated with older and/or heavier calves at weaning, from a given size cow. The general conclusion from a cow-calf unit standpoint, was that calves slaughtered at 12mm fat cover seemed to be the most ideal when efficiency of production, based on liveweight and carcass weight, was considered.

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