Masters Theses

Date of Award

8-1990

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

W.R. Backus

Committee Members

R.R. Shrode, M.J. Riemann

Abstract

The selection practiced in the beef industry lacks uniformity because breeders are unaware of the potential effects on lifetime productivity when certain traits are emphasized in a selection program. This study involved data collected from 120 Angus and 90 Polled Hereford cows and their progeny (913 calves) over a five year period (1985 to 1989). Data were obtained from the calves at weaning, cows at weaning of calf, calves at a year of age, and from the 1988 calves at slaughter. These data were analyzed, and correlations involving both live-animal and carcass variables were calculated from the error line in an analysis conducted according to SAS (1985). The initial Angus cows were randomly divided into groups: control group in which no selection would be practiced, a group in which increased maternal milk production would be favored by selection (referred to as the "maternal" group), a group in which increased yearling weight would be favored by selection (referred to as the "yearling weight" group), and a group in which both of these criteria of selection would be used (referred to as the "composite" group). The Poiled Herefords, because of a smaller number of available cows, were divided into only three groups: control, maternal, yearling weight. Inferences were drawn as to the possible relative effectiveness of using either of these traits or a combination of them as the basis for selection. Changes in cow efficiency, defined as the ratio of adjusted 205-day weight of calf to actual cow weight at weaning of calf, in these selection systems were compared.

Upon visual evaluation of the means, it was apparent that the most efficient 1989 Angus group was the composite (50.3%). The most efficient 1989 Polled Hereford group was the control (39.5%). No complete comparison between the herds can be made due to absence of a composite group in the Polled Herefords. In both herds, the least efficient group was the maternal (45.7%, Angus and 38.2%, Polled Hereford). Trends toward improved cow efficiency were observed in the Angus herd between 1985 and 1989. Cows that failed to calve were the least efficient and in both herds, were fatter and heavier at time of calf weaning. In visually evaluating the mean adjusted 205-day weight, mean adjusted 365-day, and mean adjusted 550-day weight, there appeared to be some improvement between 1985 and 1989 in the Angus herd and less improvement in the Polled Hereford herd. One major problem when selecting solely for maternal milk production is that heifers tend to become too fat. There was an increase of .2 mm backfat in the Angus herd and .4 mm in the Polled Hereford herd. Carcass data from 1988 steers were analyzed, and the mean yield grade and quality grade of carcasses from the Angus composite group were 2.8 and high Select (11.8), respectively. The analysis of the carcass data was across herds. Yield grade was correlated with fat thickness (.89) and %KPH (.72). Quality grade was correlated with marbling (.7). Percentage cutability was correlated negatively with fat thickness (-.88) and yield grade (-.99).

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