Effect of Feed Intake and Exogenous Porcine Somatotropin on Longissimus Muscle Fiber Characteristics of Pigs Weighing 55 Kilograms Live Weight

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Abstract
Thirty two barrows were used in a 2 × 3 factorial arrangement to evaluate the effects of porcine somatotropin (pST) administration (USDA-pGH-B1; 0 and 100 µgºkg BW−1 · d−1) and feed intake (FI; ad libitum [A], 1.64 [R1:80% of A] and 1.38 [R2:60% of A] kg/d) on longissimus (LM) muscle fiber characteristics of pigs growing from 25 to 55 kg live weight. The administration of pST resulted in an increase (P < .05) in muscle fiber size (all three fiber types) and shear-force (17.1%). The percentage of muscle fiber types was not affected by pST treatment. Feeding of the diet at restricted levels (R1 and R2) resulted in smaller (P < .05) βR and αW fibers compared with feeding ad libitum. Pigs with ad libitum access to their diet had fewer aR fibers and more aW fibers in the LM compared with those fed at R1 and R2 levels. Restricted feed intake (R1 and R2) resulted in lower (P < .05) shear-force values compared with ad libitum feeding. The present study indicates that pST administration of young barrows results in an increase in muscle hypertrophy. Restricted FI reduces both transformation from αR to αW fibers and muscle fiber hypertrophy. Copyright © 1988. American Society of Animal Science . Copyright 1988 by American Society of Animal Science