Masters Theses

Date of Award

12-1979

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

E. R. Lidvall

Committee Members

W. T. Butts Jr., W. R. Backus

Abstract

Data from 687 steer calves of two breed groups, British (Angus, Hereford, Angus X Hereford) and Charolais crosses, formed the basis of this study. The steers were purchased through East Tennessee Graded Feeder Calf sales and represented Prime, Choice and Good grades with a mean weight of 566 lbs. The steers were fed ad libitum corn silage for a 3-4-week period while being allowed to adjust and recover from the stresses of weaning and shipment. Following the adjustment period, the steers were weighed, photographed, sonorayed for fat thickness, measured for shoulder width and subjectively evaluated independently by committees of 10, 16 and 14 graders in 1976, 1977 and 1978, respectively. All steers were subjectively scored on a 1-15 basis for height, length, overall frame size, general trimness, head shape and muscle expression. Fat thickness was estimated in millimeters, age in months and predicted slaughter weight in pounds. For analyses, each year the graders were divided into three categories according to their training and experience. In 1976 and 1977, approximately 30 days prior to the scoring by the committees, the steers were scored by an experienced grader who was a member of the evaluation committee. The 1976 steers were randomly divided within breed and feeder grade into two ration groups of high and medium levels of energy. The steers were weighed and sonorayed for fat thickness at 14-day intervals until they reached 12 mm of fat thickness at which time they were slaughtered. Days on feed were calculated, and the carcass traits of weight, yield grade and quality grade were recorded. It was found by multiple regression analysis that models describing frame, fat and muscle accounted for 58%, 43% and 19% of the variation, respectively. Graders utilized height, depth and fat in estimating frame and fat, while width was the major factor in estimating muscle. Length and weight did not affect graders in their evaluations. There was more agreement among graders within grader category for frame and muscle, while there was greater agreement for fat among grader categories. Increases in R-squares of .01, .01 and .02 for frame, fat and muscle, respectively, were found when height-grader interactions were added to the models. Similar increases of .02, .03 and .03 in R-squares were attained when breed group-grader interactions were added to models for frame, fat and muscle, respectively. These small increases would indicate that graders handled the effects of height and breed group in a like manner. Partial regression coefficients indicated that larger framed steers were evaluated as being taller, slightly longer, shallower, narrower and leaner. When estimated fat increased, calves were seen as being lower set, slightly shorter, deeper, wider and fatter. Steers that were scored high for muscle (muscle expression) were evaluated as being lower set, longer, shallower and wider by the graders. Coefficients of correlation among graders were performed on a within-year and within year-breed group basis to further define agreement among graders. Coefficients for frame score ranged from .70-.95, .51-.86 and .58-.96 within year and .54-.93, .45-.89 and .56-.96 within year-breed group for 1976, 1977 and 1978, respectively. Somewhat less agreement was found for estimated fat where coefficients ranged from .45-.79, .20-.76 and .38-.85 within year and .34-.73, .14-.71 and .29-.83 within year and breed group for 1976, 1977 and 1978, respectively. Considerably less agreement was found for muscle score where coefficients ranged from .14-.58, -.07-.57 and .16-.72 within year and .13-.59, -.09-.61 and .16-.70 within year and breed group for 1976, 1977 and 1978, respectively. Coefficients of determination between scoring times by one grader in 1976 and 1977 indicated that steers were more accurately redescribed for body dimension rather than for fat, trimness and muscle expression. The failure to accurately describe fat, trimness and muscle expression may be due, in large measure, to weight gain and environmental influences during the 30-day period between evaluations. R-squares for grader predictions of carcass weight and days on feed were .57-.62 and .52-.56, respectively. R-squares for yield grade, .07-.14, and carcass quality grade, .06-.10, were smaller; however, the steers were slaughtered on a fat constant basis, thus reducing the total variation. Although grader experiences and the weighting of variables by the graders varied, similar variation was explained.

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