Doctoral Dissertations

Date of Award

3-1971

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

R.R. Shrode

Committee Members

C.S. Hobbs, Wm. R. Backus, S.A. Griffin, L.M. Josephson, D.O. Richardson

Abstract

A study involving 36 experimental and 8 observation pigs was conducted to acquire basic knowledge concerning body composition and development patterns of the growing meat-type pig. Linear measurements of muscle, fat, and bone were obtained on two boars, two barrows, and two gilts from each of six litters at three-week intervals up to a weight of 175 pounds and at two-week intervals up to 225 pounds when half of the pigs were slaughtered. Measurements were continued at two-week intervals on the remaining pigs to their slaughter weight of 300 pounds. A boar, gilt, and barrow from each litter were slaughtered at 225 pounds, and the remaining littermates were slaughtered at 300 pounds. Specific gravity, routine carcass data, pork quality determinations, and chemical composition data were obtained on each carcass. In addition, chemical composition data were collected on three pigs comparable to the experimental pigs at each of the observation weights of 75 and 150 pounds.

Boars had a higher accumulative average daily gain than barrows and gilts up to 225 pounds, and barrows gained faster than gilts. The advantage of boars over barrows and gilts became more evident at weights beyond 225 pounds. Boars converted feed more efficiently than barrows. The feed efficiency advantage for boars over barrows and gilts was much greater at 300 than at 225 pounds as boars were only slightly less efficient between 225 and 300 pounds than from 75 to 225 pounds.

Both skeleton and muscle had attained a greater percentage of their final 225- or 300-pound measurement at 75 pounds than had fat. The rate of increase of skeletal size was slower than muscular growth, and both skeleton and muscle developed at a slower rate than fat from 75 to 300 pounds.

The rate of increase in fat depth became more rapid at weights beyond 150 pounds, and, also, differences among individuals and sexes became more apparent. The rapid growth and increase in variation among individuals was largely due to the rapid rate of increase in depth of the second and third fat layers. About 75 to 80 percent of the third fat layer depth at 300 pounds was deposited between 225 and 300 pounds.

Ultrasonic estimates and carcass measures of fatness at the tenthand last-rib areas were highly correlated with percent lean cuts, percent ether extract, and percent protein in the carcass. Measurements obtained over the 1. dorsi on both the live animal and carcass were more highly correlated with carcass composition than were midline measurements of live-animal and carcass fatness. At 225 pounds, correlations involving depth of the first two fat layers were higher than those that included all three fat layers. However, at 300 pounds correlations including layers 1, 2, and 3 were as high or higher than those with only layers 1 and 2 included.

The percentages of total body length constituted by each body section (poll to scapula, scapula to last rib, last rib to illium, and illium to root of tail) were similar at all weights.

Correlations between carcass length and measures of fatness and muscling were of much greater magnitude at 300 than at 225 pounds. This indicates that the pigs which continued to grow skeleton from 225 to 300 pounds remained lean and continued to grow muscle; whereas, pigs that had a slower increase in skeletal growth tended to become fat and also had a slower rate of muscular growth than the longer pigs.

These data indicate that individual differences become more evident at heavier weights and that these differences are more observable by practical methods of live-animal evaluation at the heavier weights. Therefore, for most effective results, selection of prospective breeding animals, especially boars, should be conducted at weights beyond 200 pounds.

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