Doctoral Dissertations

Date of Award

12-1972

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

William R. Backus

Committee Members

J. B. McLaren, S. L. Hansard, K. M. Barth, W. W. Overcast, R. E. Beauchene, R. S. Dotson

Abstract

Data from 145 weanling Hereford heifers were used to determine the relationship of feeder grade, weight, fat thickness and measures of skeletal size and shape to feedlot performance and carcass characteristics. Data from this group of animals (lOGD Heifers) were also used to derive a more objective method of lotting feeder cattle into outcome groups based on the magnitude of canonical variable index scores. An independent group of 103 Hereford heifers (IT Heifers) were used to test the application of the index scores and outcome grouping technique derived from the lOGD Heifers. Feeder grades were Medium, Good and Choice for both the lOGD Heifers and the IT Heifers. Animals were randomly allotted by grade and weight to pens of six heifers each. They were fed a ration of ad libitum corn silage treated at ensiling with 10 lb. each of urea and limestone plus 6 lb. per head, per day of concentrate designed to supply adequate protein for a roughage phase. They were removed from test and sent to slaughter at predesignated fat thickness levels. Those heifers which did not reach the predesignated fat thickness level by the end of roughage phase were then fed a finishing ration of eight parts ground shelled corn to one part 41 percent cottonseed meal plus 4 lb. of hay per day. They were weighed and sonorayed at 28 and 14 day intervals during the roughage and finishing phases, respectively. Photographic measurements of skeletal size were taken at the beginning and end of testing. Canonical correlation analyses showed a highly significant (P > .0001) relationship (R=.76) between feeder grade and weight and days and weight to a constant compositional end-point of 10 mm. fat thickness, A highly significant (P > .0001) relationship (R=.77) was also found between initial subcutaneous fat thickness, weight, and measures of skeletal size and days and weight to 10 mm. fat thickness. In a comparison of the total variation in feedlot performance accounted for by these analyses, the system using initial fat thickness, weight and measures of skeletal size accounted for 5.4 percent more variation in days and weight to 10 mm, fat thickness than the historic feeder grade and weight method. Lotting feeder cattle into outcome groups of various skeletal sizes and fatness has implications for improving present feeder cattle marketing and feedlot management practices of Hereford heifers. Heifers in outcome groups describing heavier, larger framed animals, regardless of initial fatness, required fewer days to reach 10 mm. fat thickness and were heavier at this point than lighter, smaller framed heifers. Heifers in outcome groups describing fatter animals, regardless of initial skeletal size, required less time in the feedlot to reach 10 mm, but, were lighter at this point than initially thinner calves. When these various kinds of cattle were fed to the same compositional endpoint, the variation in carcass quality and yield grade was eliminated.

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