The effects of porcine somatotropin, gender and porcine stress syndrome on growth, carcass composition and pork quality

Lacombe breed pigs (72 gilts, 72 barrows) of three genotypes with respect to the porcine stress syndrome (normal, heterozygous, or homozygous for the halothane gene), were treated from 57 to 106 kg body weight with daily injections of 0.9% saline containing 0 or 3 mg of recombinant porcine somatotropin (pST) in a randomized block design. Pigs receiving pST had lower average daily feed intakes (ADF), greater average daily gains (ADG) and lower feed conversion efficiencies (FCE). Gilts relative to barrows had lower ADG, ADF and higher FCE. Gilts versus barrows and pigs treated with pST had reduced fat depths and greater loin depths at the 10th rib. Pigs homozygous for the halothane gene had reduced loin lean structure and color scores, greater light reflectance (L*), and lower soluble protein contents as expected, and these genotypic effects did not interact with pST treatment. Sex by pST treatment interactions (P < 0.05) were found for loin depth, moisture content, color score and L* values indicating barrows respond more favorably to pST treatment than gilts. Generally, pST treatment, gilts relative to barrows, and possession of the halothane gene increased carcass lean and reduced subcutaneous fat levels. Sex by pST treatment interactions were found for picnic lean (lower shoulder; P < 0.05), ham lean (P < 0.05), and total carcass lean (P = 0.09) further supporting the theory that barrows benefit more than gilts to pST treatment. No significant interactions were found between genotype and pST treatment for any qualitative muscle traits. Thus, pST treatment had no direct effect on meat quality and was not found to interact with the halothane gene. However, pST interactions with sex indicated barrows respond quantitatively and qualitatively more favorably than gilts to pST treatment. Key words: Somatotropin, porcine somatotropin, pork, porcine stress syndrome, stress, pigs, growth