Effect of Pre-natal Runting on the Post-natal Development of Skeletal Muscles in Swine and Rats2

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Abstract
Pre-natal runt and high-weight (birth), litter-mate control animals were selected at day of birth from swine and rat litters. All animals were suckled normally and then fed an adequate diet. The runt pigs required a significantly longer time (23 days) to reach 106 kg than their control littermates. In swine, runts had significantly lower body weights and, in general, smaller muscles but no difference in muscle fiber diameters at day of birth. Runt pigs at similar adult weights to the control pigs had larger muscle fiber diameters in two of four muscles studied and larger quantities of intramuscular lipid in three of the four muscles. In two of the muscles where length (based on bone length) and fat-free weight were similar between runt and control pigs, it was possible to infer that the significantly larger muscle fiber diameter in the muscles of the runt pigs must have been associated with fewer muscle cells. At a similar adult body weight, runt and control pigs had similar loineye areas, average backfat thickness, quantity of perirenal fat, and weight or length of three bones. The adrenal weight was significantly heavier in the adult control compared to the runt pigs. Runt and control rats studied at three different body weights had similar muscle weights, muscle fiber diameters and bone lengths. Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.