Masters Theses

Date of Award

8-1983

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

James Riemann

Committee Members

Sharon L. Melton, Curtis C. Melton, & W.R. Backus

Abstract

Eighty-one Hereford steers were backgrounded on fescue-orchard grass-clover pasture and then removed after summer grazing and assigned subjective scores for frame size and muscling. Steers were then fed whole shelled corn ad libitum for 0, 28, 56, 84, 112, and 140 days on feed (DOF), evaluated for performance traits and slaughtered. Carcass data were collected then the left side of each carcass was fabricated and evaluated for various yield, quality, chemical, physical, and palatability characteristics.

Large framed steers had heavier live weights (P<.05) and were taller at the withers (P<.05) than small framed steers throughout the forage feeding phase. All frame size groups were similar in ultrasonic fat thickness measurements during forage feeding.

During grain-finishing, the large framed steers were taller (P<.05) at the withers than the small-framed cattle through 140 DOF but past 28 DOF no advantage in frame size, with respect to live weights was discovered. Live fat thickness measurements did not differ (P>.05) among frame size groups. The small framed cattle gained slightly more during grain-finishing than the medium and large framed steers, but no difference (P>.05) was observed among frame size groups for average daily gain or feed efficiency.

Slaughter weight, wither height, fat thickness, and weight gain increased (P<.05) as DOF increased. Differences in average daily gain and feed efficiency were not related with time on feed.

Dressing percent, hot carcass weight, adjusted fat thickness, rib eye area and percentage of kidney, pelvic, and heart fat increased (P<.05) as the length of grain feeding time increased. Yield grade increased (P<.05) with time on feed, remaining within yield grade (1) through 5 DOF, then increased within yield grade (2) through 140 DOF. Marbling degree and quality grade increased (P<.05) as a result of increased grain feeding time. Mean quality grade of low Choice was obtained after 140 DOF. Lean color scores were not affected (P>.05) by DOF, but lean firmness scores increased (P<.05) and external fat generally became whiter as a result of increased DOF.

The proportion of various wholesale cut weights to side weight was affected slightly by live animal frame size except for the proportion of the wholesale round which was higher (P<.05) for the large frame size group than the small. The proportions of wholesale cuts were affected by DOF. Chuck, round, and foreshank proportion of the side weight were found to decrease (P<.05) as DOF increased whereas proportion of the rib, brisket, plate, and flank cuts increased (P<.05) as DOF increased. Proportion of the loin neither increased or decreased, over time, during grain-finishing.

The Biceps femoris muscle weight and area, and femur length were found to increase (P<.05) as DOF increased, but femur weights were similar after 28 DOF. Muscle: bone ratio increased (P<.05) from 0 to 140 DOF but had a low correlation with live animal measurements and muscling score.

Moisture percentage of the longissimus muscle decreased (P<.05) and ether extract increased as DOF increased but not linearly with DOF. Nonvolatile cooking loss was affected (P<.01) by DOF and increased with increased grain feeding time, but volatile and total cooking loss were not influenced (P>.05) by DOF. Nonvolatile cooking loss was more closely correlated with carcass fat thickness than marbling degree but both were significant relationships (P<.001).

Taste panel scores for all palatability traits generally increased (P<.05) as DOF increased and steaks from forage-fed steers (0 DOF) were less desirable for flavor, juiciness, and overall acceptability than steaks from grain-fed steers. Tenderness scores through 112 DOF were not significantly different (P>.05) but steaks from steers fed 140 DOF were rated as being more tender (P<.05) than steaks from all other DOF groups. Warner-Bratzler shear values were not affected (P>.05) by length of grain feeding but steaks from 140 DOF group steers had the lowest shear values.

Steaks from carcasses with .2 in. of fat or less had lower (P<.05) scores for flavor and overall acceptability than those with more than .2 in. of external fat. However, carcasses with more than .2 in. of fat had little advantage in tenderness over carcasses having .2 in. of fat or less.

Scores for palatability traits improved as marbling degree increased from practically devoid through small, but steaks with modest marbling had lower flavor and juiciness scores and were significantly less tender (P<.05), according to taste panel evaluations than were Good or Standard grade steaks. Flavor and juiciness ratings were lower (P<.05) for steaks from Standard grade carcasses. Marbling was more closely correlated with taste panel flavor scores than tenderness scores.

It was concluded that subjective scores for frame size and muscling have little, if any, benefit in the selection of steers for increased performance. Grain feeding for 140 days, minimum, is required for Hereford steers to reach the low Choice carcass grade. However, feeding steers past 84 days on corn appears to benefit the palatability of beef top loin steaks slightly.

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