Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science

First Advisor

Lauren L. Christian


Ninety-six crossbred pigs of known stress-susceptibility genotype were used to determine effects of a recombinantly-derived analog of porcine somatotropin (rpST) on performance traits, quantitative and qualitative carcass characteristics and leg soundness. Feed consumption was significantly reduced with rpST and feed conversion improved across all genotypes. A treatment x genotype interaction suggested greater rpST-elicited improvement in feed efficiency within stress-negative genotype. Barrows also responded in a differential manner to rpST with a more definitive improvement in feed conversion relative to controls than was observed for treated gilts. Treatment with rpST increased lean accretion and reduced fat deposition of all genotypes as depicted by increased longissimus muscle areas and reduced average backfat thicknesses. Lean, bone and skin weights increased as a percentage of side weight while adipose tissue decreased in carcasses from treated animals. Proximate analysis of dissected lean and adipose tissues revealed increased percent protein and moisture but a reduction in percent lipid associated with rpST-treatment. Trimmed wholesale cuts of the ham, loin, Boston butt and picnic shoulder also increased as a proportion of side carcass weight due to the repartitioning effect of rpST. Qualitative muscle trait measurements of ultimate pH, visual color, reflectance and transmittance values improved markedly within animals of the stress-positive genotype receiving rpST;Front leg structure and movement as well as rear leg movement scores were observed reflecting a less smooth, more choppy stride for rpST-treated animals. Enhanced muscle development within shoulder and ham regions was the primary cause of this reduced mobility. Rear hock angulation and rear toe size did not differ between rpST-treated groups. Higher composite osteochondrosis score in the forelimb of treated animal resulted from greater incidence of joint lesions at the proximal humerus and proximal radius-ulna locations. Osteochondrosis values were similar for the distal humerus and distal radius-ulna and for the composite value generated from the four joint surface evaluations of hind limb;In summary, rpST improved feed:gain and lean:fat ratios within treated animals, had a beneficial effect on several muscle quality characteristics of the stress-positive genotype, and slightly reduced fore- and rear-leg mobility.



Digital Repository @ Iowa State University,

Copyright Owner

Chris Lee Skaggs



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165 pages