Doctoral Dissertations

Date of Award

3-1973

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

J. B. McLaren

Committee Members

Wm. R. Backus, Curtis C. Melton, Karl M. Barth, W. W. Overcast, Melvin Johnston

Abstract

Performance of 65 steers and heifers from Hereford (H) dams and sired by either a H, Maine-Anjou (MA), Simmental (S), Limousin (L) or a Charolais (C) bull or from Charolais X Hereford (CH) dams and sired by either a H or C bull was evaluated at various intervals from birth to weaning. Calves were born in February and March and nursed the cows without creep feed during the summer grazing season. Forty-five of these animals were selected at weaning and were fed a daily ration of 6 lb. shelled com, 3 lb. legume hay and late dent corn silage ad libitum per head (roughage feeding phase). Follow-ing the roughage phase, animals were fed a daily concentrate ration consisting of 2 lb. of shelled corn per 100 lb. of weight and 6 lb. of legume hay until the predetermined fat thickness level (0.40 in.) over the longissimus dorsi muscle was attained. Animals then were slaughtered and carcasses evaluated with respect to U.S.D.A. quality and retail yield traits. A representative retail cut from each carcass was subjected to organoleptic and chemical evaluations. Least squares procedures as described by Harvey (1960) were used to evaluate differences among breed groups with respect to growth rate, carcass traits and meat palatability. Orthogonal contrasts were used for mean separation when significant differences were observed. Three breed comparisons were of primary interest. These contrasts compared H calves to all F1 calves, MA X H calves to other F1 calves, and H X CH to C X CH calves. Hereford calves were fatter (P < .01) than F1 calves at the end of the roughage phase. Mean subcutaneous fat thickness for H calves was 0.36 in. MA X H, S X H and L X H measured about 0.18 in. fat thickness. C X H, H X CH and C X CH were intermediate with respect to fatness and averaged about 0.25 in. after 140-days roughage feeding. All animals with less than 0.40 in. subcutaneous fat were fed a concentrate ration until an estimated fat thickness of 0.40 in. was attained. H calves attained this predetermined level of fatness at a lighter (P < .05) weight, a younger (P < .05) age and required fewer (P < .01) days on feed than F1 calves. MA X H calves were heavier (P < .01) and had maintained a higher (P < .01) lifetime growth rate than the other F1 calves. No differences were found between F1 calves with respect to final age. Heifers fattened faster (P < .01) than steers and had lower (P < .01) total gains on feed. Differences in carcass dollar value were directly related to carcass weight. No breed or sex differences were found with respect to carcass value per cwt. All breeds were similar with respect to U.S.D.A. carcass quality grade and other quality attributes. Carcasses from MA X H, S X H and C X CH groups graded an average of low choice. All other breeds graded high good. Differences in estimates of carcass retail yield were associated with differences in carcass fatness and were significant (P < .01) between H X CH and C X CH carcasses and between steer and heifer carcasses; however, steers also had larger (P < .01) l. dorsi muscle areas and less (P < .01) actual kidney, heart and pelvic fat than heifers. No significant trends were found with respect to palatability or Warner-Bratzler shear of cooked meat from these animals. F1crosses were similar to H with respect to organoleptic scores; however, roasts from H carcasses had lower (P < .05) Warner-Bratzler shear values than roasts from F1 calves. Sex of calf significantly (P < .05) affected percent lipid in a sample of the l. dorsi muscle. Other sources of variation in muscle lipid content were not significant. A significant (P < .001) rank correlation of (r = 0.83) existed between rank of panel tenderness scores and rank of Warner-Bratzler shear values.

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