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Title: Effects of a “step-up” ractopamine feeding program, sex and social rank on growth performance, hoof lesions, and Enterobacteriaceae shedding in finishing pigs

item Rostagno, Marcos
item Marchant, Jeremy

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2008
Publication Date: 1/1/2009
Citation: Poletto, R., Rostagno, M.H., Richert, B.T., Marchant Forde, J.N. 2009. Effects of a “step-up” ractopamine feeding program, sex and social rank on growth performance, hoof lesions, and Enterobacteriaceae shedding in finishing pigs . Journal of Animal Science. 87(1):304-313.

Interpretive Summary: Ractopamine is marketed under the trade name Paylean as a repartitioning agent for use in finishing pigs. It is a adrenergic agonist which alters cell metabolism to build up protein (or lean muscle) and decrease fat, resulting in a leaner carcass for the consumer and increasing feed conversion to give the producer economic benefits. However, our earlier work has shown that when it is fed to finishing pigs, they become more active, are harder to handle and have physiological changes indicative of increased stress, such as higher heart rates and higher circulating epinephrine levels. The aim of the current study was to see if ractopamine had an effect on pig health - specifically the shedding of bacteria associated with food safety and hoof health. We also investigated relationships of these measures with social status of the pig within its group and with gender. Our results confirmed that ractopamine did enhance production performance and growth and the benefits increased with increasing social status. We did not detect any shedding of Salmonella at any time point but we did find that overall Enterobacteriaceae shedding was higher in ractopamine-fed pigs than control-fed pigs. However, on the day of slaughter, shedding levels were actually less in ractopamine-fed pigs than control-fed pigs. Bacterial shedding was also higher in gilts than in barrows, but was not affected by social status. Ractopamine-fed pigs had more splits, cracks and bruises in their hooves, but these injuries did not result in increased incidence of clinical lameness. Altogether, these results imply that ractopamine influences intestinal microbial populations and fecal shedding of Enterobacteriaceae that can be pathogenic to animals and humans, but further research is required to quantify real risks to human health. Hoof structure may also be affected by a potential effect of ractopamine on hoof horn production, but again, further research is needed to elucidate any causal relationship between ractopamine and hoof health. Our results are therefore important to researchers as they highlight potential challenges for further study.

Technical Abstract: Increasing concern for animal well-being and food safety has driven the investigation of feed additives such as ractopamine (RAC), a ß-agonist widely used to improve production performance of finishing pigs. The objective of this study was to determine the effects of a “step-up” RAC feeding program (5 ppm/ 2wk followed by 10 ppm/2wk) on production performance, Enterobacteriaceae shedding, including Salmonella, and hoof lesions in relation to social rank. Sixty-four 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 post-mixing by behavioral observation. Fecal samples were collected once/wk for 5 wk. At slaughter, 32 dominant and subordinate barrows and gilts (16/gender) were examined for hoof lesions and carcass yield, and luminal contents from ileum, cecum and rectum were collected. RAC-fed gilts and barrows showed enhanced performance and growth (P < 0.05). Increasing social rank of animals also tended to enhance performance (P < 0.1). Gilts gained more backfat depth when comparing to baseline values at both 10th and last ribs, while loin eye area increased at similar rate for both barrows and gilts (P < 0.05); however, no significant effect of RAC feeding was found on these measures (P > 0.1). At slaughter, RAC-fed pigs had higher live BW, HCW (P < 0.05) but only numerically greater carcass yield. Despite the positive effects of RAC feeding on growth performance, pigs fed the compound showed higher 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. However, animals fed RAC peaked Enterobacteriaceae shedding levels during the first week of feeding, but progressively decreased until slaughter, when rectal and cecal levels were lower than in CTL pigs (P < 0.05). Social rank tended to affect gut Enterobacteriaceae populations of barrows more than gilts (P < 0.1). Additional research is needed to further explore the effects of RAC feeding on hoof soundness and Enterobacteriaceae populations in the gastrointestinal tract of finishing pigs. It is also proposed to integrate individuals’ social rank when possible, as it may interfere with treatment responses.