Sex and porcine somatotropin impact on variation in growth performance and back fat thickness

Abstract

Managing variation in carcass weight and composition is an enormous challenge for the pig producer. A means of improving growth performance and reducing back fat is porcine exogenous somatotropin (pST) treatment. It is possible that this technology may also reduce variation in these important growth and carcass parameters. This study was conducted to provide data on the effect of sex and pST on variation in growth and carcass characteristics. Sixteen on-farm studies involving 1495 pigs were conducted in various states within Australia. On each farm, groups of pigs were randomly assigned within sex to one of 2 management regimes (control or pST regime). The control regime consisted of feeding the typical finisher diet used on that farm while the pST regime involved feeding the typical grower diet used on the farm combined with daily injections of pST (5 mg/day). Data from individual pigs were collated and the summary descriptive statistics derived for each treatment group on each farm were then analysed. Daily liveweight gain was lower and feed conversion ratio (FCR) and back fat at the P2 site were higher in gilts than in boars. The pST regime increased average mean daily gain and reduced feed intake, FCR and back fat at the P2 site. The coefficient of variation (CV) around live daily gain was lower in gilts than in boars (19.3 v 22.3% for gilts and boars, respectively, P<0.001) and in pigs treated with the pST regime (22.1 v. 19.9% for the control and pST regimes, respectively, P<0.001). The CV around liveweight was higher in the control boars than in any of the other treatment groups as indicated by the main (P<0.001) and interactive (P<0.001) effects of both sex and pST regime. The coefficient of variation around P2 was reduced by pST (16.2 v. 14.2%, P<0.001) but was not different between gilts and boars. There was an interaction (P = 0.025) between pST regime and sex with the average kurtosis for the P2 distribution positive in gilts treated with pST but slightly negative in all the other groups. The distributions were on average skewed to the right, particularly in gilts (P = 0.017) and in pigs treated with pST (P<0.001). In conclusion, these data demonstrate that as well as improving mean final liveweight and P2 back fat, pST treatment can also reduce variation in these key production parameters that form the basis for economic returns to the producer.