Metabolic and production responses to different porcine somatotropin injection regimes in pigs

Abstract

Thirty-two female crossbred pigs (initial weight 75 kg) were used in this experiment to investigate the effect of differing porcine somatotropin (pST) regimes on growth performance. Pigs were kept in individual pens and fed ad libitum a wheat-based diet formulated to contain 14.4 MJ DE/kg and 180 g ideal protein/kg. Treatments were daily injection with saline (Sal), daily injection with pST (5 mg) (D), bi-daily injection with pST (10 mg) (2D), and injection with pST (12 mg) every Monday, Wednesday, and Friday (MWF). On the days that pigs were not receiving pST they were injected with saline (0.5 mL). All pST regimes caused a reduction (P < 0.001) in feed intake and feed conversion ratio (FCR), although there was no significant effect on average daily gain. Feed intake decreased after the first injection and, for the D group, remained low and constant. Feed intake for the 2D group was also reduced but not to as great an extent as for the D group. Feed intake in the MWF group showed a clear temporal response, being low during the week but increasing over the latter part of the weekend. Thus, feed intake from Sunday until Monday mornings was 400 g greater (P < 0.001) than from Saturday until Sunday mornings. Therefore, it appears that the effects of pST on feed intake may be reduced when a 3-day interval is used between injections. Back fat was significantly reduced with all pST injection regimes, whereas estimated fat deposition was only significantly reduced in the D and 2D pigs. Plasma urea nitrogen was increased, whereas glucose was decreased during pST administration and the average concentrations of both metabolites during the first week of administration were strongly related (P < 0.001) to FCR over the full 3 weeks of the study (R = 0.733 and -0.683, respectively). Although daily injection with pST appears to give the greatest reduction in feed intake and fat deposition, an alternative pST injection regime involving less frequent pST injections can also improve growth performance similarly in finisher pigs.