Porcine somatotropin improves growth in finishing pigs without altering calpain 3 (p34) or alpha-actin mRNA abundance and has a differential effect on calpastatin transcription products

The objective of this study was to determine whether the improvements in growth and efficiency of gain achieved by recombinant porcine somatotropin (pST) are associated with altered expression of the p94, calpastatin, or alpha-actin genes in porcine longissimus (LD) muscle. Forty-eight barrows (initial 64.2 to 67.4 kg BW) were assigned to four treatments (n = 12) arranged as a 2 X 2 factorial in a randomized complete block design. Factors were duration of treatment (3 or 6 wk) and pST administration (0 or 3 mg(.)pig-1(.)d-1). Plasma samples were obtained 24 h after the first pST injection and at the end of the each treatment period for assays of selected variables. The LD samples were obtained at 3 and 6 wk of pST treatment. Northern blot analysis of calpastatin expression in LD muscle revealed three distinct transcription products of approximately 8.5 (CPST I), 5.5 (CPST II), and 2.5 (CPST III) kb; CPST II was reduced (P .02) 33 and 61% by pST at 3 and 6 wk, respectively, whereas CPST I and III were not influenced (P .12). Neither alpha-actin nor p94 was responsive to pST injection. As expected, pST resulted in higher (50%, P .02) plasma insulin within 24 h and one- and twofold higher (P .01) concentrations at 3 and 6 wk, respectively. Glucose was increased (P .01) at 3 (15%) and 6 (10%) wk, whereas urea nitrogen was reduced (32 to 36%, P .01). The efficacy of pST was evident in that ADG was improved (P .01) 11 to 13% independent of time. Likewise, feed intake was reduced (P .01) 10 to 11% and gain: feed improved (P .01) approximately 26% for pigs receiving pST independent of time. These data indicate that the enhanced muscle growth achieved by pST is not associated with altered expression of p94 or alpha-actin, or an increase in the abundance of any calpastatin transcription product