Removal of both zinc oxide and avilamycin from the post-weaning piglet diet: consequences for performance through to slaughter

Avilamycin (AGP) and zinc oxide (ZnO) are both frequently included in the post-weaning piglet diet to enhance growth performance and prevent diarrhoea. This study investigated what effect removing these compounds from the post-weaning diet would have on the growth performance and faecal microbiota of weaned piglets. Fifty-two crossbred piglets (JSR Healthbred) were allocated, at weaning, to one of two dietary treatments on the basis of weight, litter origin and gender. The diets were (i) control (no supplemented ZnO or AGP); (ii) ZnO + AGP (supplemented with 3100 mg ZnO per kg food and 40 mg avilamycin per kg food). These diets were offered ad libitum for 20 days post weaning. Thereafter, the pigs received the same non-supplemented grower and finisher diets ad libitum. All piglets were individually weighed, and faecal samples were obtained from pre-selected piglets, at various time points throughout the trial period. Ten-fold serial dilutions of faecal material were cultured on specific media to enumerate aerobes, anaerobes, Lactobacillus spp. and Escherichia coli. ZnO + AGP supplementation enhanced weaned piglet average daily food intake (ADFI) (P < 0.001), average daily live-weight gain (ADG) (P < 0.001) and food conversion ratio (FCR) (P < 0.01) during the initial 20 days post weaning. Piglets previously supplemented with ZnO + AGP gained more weight per day during the non-supplemented grower phase (days 21 to 60) than their control counterparts (741.5 v. 672.5 g per pig per day) (P < 0.01). The bacteriological data showed that ZnO + AGP piglets had lower counts of anaerobic bacteria in their faeces than control piglets (P < 0.01). These findings indicate that dietary AGP + ZnO may enhance growth by reducing gastro-intestinal bacterial populations, and that their removal from the post-weaning diet will increase days to slaughter.