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Effects of a "step-up" ractopamine feeding program, gender and social rank on growth performance, hoof lesions and Enterobacteriaceae shedding in finishing pigs

R. Poletto^*,, M. H. Rostagno^*, B. T. Richert and J. N. Marchant-Forde^*

^* USDA-ARS Livestock Behavior Research Unit, West Lafayette, IN 47907 Department of Animal Sciences, Purdue University, West Lafayette, IN 47907

Jeremy.Marchant-Forde{at}ars.usda.gov

Abstract

Increasing concern for animal well-being and food safety has stimulated the investigation of feed additives such as ractopamine (RAC), a β-agonist widely used to improve production performance of finishing pigs. The objective of this study was to determine effects of RAC feeding, delivered as a "step-up" program (5 mg/kg for 2 wk followed by 10 mg/kg for 2 wk), on growth performance, Enterobacteriaceae shedding, including Salmonella, and hoof lesions, also taking into account gender and social rank of pigs. A total of 64 barrows and gilts (balanced by treatment and gender) were assigned to pens of 4 (by gender) as either control (CTL) or RAC treatment. Social ranks (dominant, intermediate, and subordinate) of pigs in each pen were determined by behavioral observation during 48 h post-mixing. Fecal samples were collected once/wk for 5 wk. At slaughter, the 32 dominant and subordinate barrows and gilts (16/gender) were examined for hoof lesions and luminal contents from ileum, cecum, and rectum were collected. Pigs fed RAC had increased growth performance (P < 0.05) with social rank of animals affecting overall ADG (P < 0.05). Gilts gained more backfat than barrows when comparing to baseline values at both 10^th and last ribs (P < 0.05), while loin eye area increased at similar rate for both barrows and gilts (P > 0.10). No significant effect of RAC feeding was found on backfat or loin eye area (P > 0.10). At slaughter, RAC-fed pigs had greater live BW (P < 0.05). Despite the positive effects of RAC feeding on growth performance, pigs fed the compound had a greater frequency of front and rear hoof lesions as did barrows and dominant individuals (P < 0.05). Detectable levels of Salmonella shedding were not identified at any time during the experiment. Enterobacteriaceae shedding levels from RAC-fed pigs peaked at the first week of feeding, and progressively decreased until slaughter. At slaughter, rectal and cecal Enterobacteriaceae levels were lower in RAC-fed pigs than in CTL pigs (P < 0.05). Social rank tended to affect gut Enterobacteriaceae populations of barrows more than in gilts (P < 0.10). The effects of RAC feeding on hoof soundness and Enterobacteriaceae populations in the gastrointestinal tract of finishing pigs warrant further investigation. It is also proposed that the integration of the individuals’ social rank status into future studies should be considered, as it may affect treatment responses.

Key Words: Enterobacteriaceae • hoof soundness • performance • ractopamine • social rank • swine

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