Masters Theses

Date of Award

3-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

E. R. Lidvall

Committee Members

H. Dwight Loveday, W. R. Backus

Abstract

Data from 144 steer calves of two breed groups, Hereford and Continental (Charolais and Simmental crosses), formed the basis of this study. The steers were purchased through graded feeder calf sales in Tennessee and were considered representative of their respective breed group.

The steers were randomly divided by breed into three frame groups; small, average and large. Within each frame-breed group, animals were randomly assigned to one of three diet groups representing three levels of energy. Treatment one consisted of whole shelled corn supplemented with Tend-R-Leen ® fed throughout the study. Treatment two groups were fed corn silage and a concentrate mixture of ground shelled corn and a commercial protein supplement. Steers in treatment three were fed a protein supplemented corn silage until 75% of the predicted slaughter weight had been obtained and then switched to the whole shelled corn and Tend-R-Leen ® diet utilized in treatment one.

The steers were weighed and u1trasonica1 1y evaluated for 12th rib fat thickness at 14 day intervals until reaching 12 mm of subcutaneous fat at which time they were slaughtered. Days on feed and average daily gain were calculated and the carcass traits of 12th rib fat, ribeye area, internal fat deposition, marbling score, quality grade and yield grade were recorded.

It was found by least squares analysis that breed group influenced (P<.001) final weight and days required to reach the desired compositional endpoint. Cattle of Continental breeding displayed heavier slaughter weights and required more time to reach the 12 mm slaughter point. No differences in average daily gain were found (P>.10) between the two breed groups.

Least squares analysis revealed that variation in dietary energy levels accounted for significant variation (P<.01) for both breed groups in the performance traits measured. Increasing the level of energy in the diet resulted in a decrease in final weight and shortened the time required to reach the compositional endpoint, while increasing the average daily gain. Dividing the diet into two stages, as in treatment three, resulted in an increase in days on feed with no advantage in final weight or average daily gain when compared to treatment two.

For the carcass traits measured, least squares analysis reveals breed group affects (P<.05) 12th rib fat, ribeye area and internal fat. Steers of Continental breeding had less subcutaneous fat, larger ribeye areas and greater internal fat deposition than cattle of Hereford type. However, when ribeye area is expressed on a 100 kg carcass weight basis there was no difference (P<.10) found between groups. No differences were found in marbling score, quality grade or yield grade. Dietary energy levels were revealed through least squares analysis to impact on the carcass traits recorded. Use of the high energy shelled corn ration in treatments one and three resulted in increased ribeye area and more desirable yield grades than treatment two. Increasing the level of energy in the diet also resulted in increased 12th rib fat, decreased internal fat and higher quality grades. Energy level did not influence marbling scores, nor was there a difference noted in ribeye area when compared on an equivalent carcass weight basis.

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