Date of Award
Master of Science
E.R. Lidvall Jr
J.B. McLaren, L. Keller
A study involving 69 experimental boars was conducted to compare tested boars indexed at weights of 200 and 250 pounds, and in an effort to develop reasonable minimum standards for average daily gain, feed per hundred-weight of gain and backfat probe fatness of boars tested to a live weight of 250 pounds. Linear measurements of length, muscular growth and fat deposition were obtained with a steel tape and a somascope at weights of 200 and 250 pounds on 40 boars from the 1970 spring and 29 boars from the 1970 fall testing periods at the UT Swine Testing Station.
Rank correlation coefficients of 0.56 and 0.64 were obtained between indices calculated from the values of traits measured at 200 and at 250 pounds for the spring and fall test periods, respectively. Change in backfat thickness resulted in a greater change in rank among the boars than did changes in other components of the index. Rank correlation coefficients of 0.47 (spring test) and 0.13 (fall test) were obtained between fat thickness at 200 and 250 pounds. Similar correlations for average daily gain and feed efficiency between 200 and 250 pounds were 0.90 (spring) and 0.20 (fall), and 0.70 (spring) and 0.99 (fall), respectively.
Average daily gain of the boars from start of test to 200 pounds was 1.79. The average daily gain of the same boars from start of test to 250 pounds was 1.86 pounds per day. Comparable figures for feed per hundred-weight of gain and backfat probes were 270 and 284, and 0.86 and 1.06, respectively. These data suggest that minimum standards for tested boars indexed at a heavier weight of 250 pounds should be a minimum of 1.70 pounds ADG, a maximum feed efficiency of 305 in spring tests and 315 pounds of feed per cwt gain during the fall test with a maximum fat probe of 1.3 inches.
Hampshire boars were leaner at both weights than were Yorkshire and Duroc boars; however, Hampshires also had a greater difference between fat thickness over the midline and at the probe site. This difference of about .05 inches of backfat would result in an advantage of four points in the selection index.
These data indicate that certain genetic differences are more apparent in boars indexed at a weight of 250 pounds as compared to a lighter weight of 200 pounds. The swine industry continues to market hogs at an average weight of about 230 pounds. Therefore, testing of prospective boars for breeding purposes may need to be continued to weights beyond 200 pounds and selection of boars made at the heavier weight if maximum accuracy is to be attained in identification of superior germ plasma.
Dixon, Marion Cornelius, "A comparison of test station standards for boars indexed at weights of 200 and 250 pounds. " Master's Thesis, University of Tennessee, 1972.