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Title: Effect of feeding ractopamine hydrochloride on growth performance and responses to handling and transport in heavy-weight pigs

Author
item PETERSON, C - University Of Illinois
item PILCHER, C - University Of Illinois
item ROTHE, H - University Of Illinois
item Marchant-Forde, Jeremy
item RITTER, M - Elanco Animal Health, Inc
item CARR, S - Elanco Animal Health, Inc
item PULS, C - University Of Illinois
item ELLILS, M - University Of Illinois

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2014
Publication Date: 2/5/2015
Citation: Peterson, C.M., Pilcher, C.M., Rothe, H.M., Marchant Forde, J.N., Ritter, M.J., Carr, S.N., Puls, C.L., Ellils, M. 2015. Effect of feeding ractopamine hydrochloride on growth performance and responses to handling and transport in heavy-weight pigs. Journal of Animal Science. 93(3):1239-1249. DOI: 10.2527/jas.2014-8303.

Interpretive Summary: Beta-agonists, such as ractopamine hydrochloride, are often used in food animal production to improve feed efficiency and increase the amount of lean tissue and decrease the amount of fat in the carcass at slaughter. However, in pigs, they have also been implicated in having negative effects on welfare, with the pigs becoming harder to handle, having elevated level of stress hormones and being more prone to stress during transportation. The current experiment investigated the effects of feeding different levels of ractopamine (0 vs. 5 vs. 7.5 mg/kg), and subjecting the pigs to different levels of handling intensity (gentle vs. moderate vs. aggressive) followed by 1 hour transportation. The results showed that pigs fed either of the ractopmaine diets did gain more weight and had better feed efficiency. However, pigs fed RAC at 7.5 mg/kg had higher plasma epinephrine concentrations and higher percentage of pigs showing skin discoloration after handling and higher incidences of being non-ambulatory during handling and transportation, regardless of handling intensity. Aggressive handling increased blood acidity and increased stress hormone concentrations. It also increased open mouth breathing and skin discoloration. These results suggest that feeding ractopamine at 5 mg/kg did not adversely affect the pigs' physiological responses to handling and transportation, but the increased dose of 7.5 mg/kg did result in increased indicators of poorer welfare and should be subject to further study.

Technical Abstract: The impact of feeding ractopamine hydrochloride (RAC) on growth performance and responses to handling and transport in heavy BW pigs was evaluated in a study carried out as a split-plot design with a 3 × 3 factorial arrangement of treatments: 1) RAC level (0 vs. 5 vs. 7.5 mg/kg); 2) Handling Intensity (HI; gentle vs. moderate vs. aggressive); RAC level was the main plot and HI was the subplot. A total of 288 pigs housed in groups of 8 were used to evaluate growth performance over a 28-d RAC feeding period (98.5 ± 4.58 kg to 131.5 ± 7.45 BW). On d 29 of the study, the HI treatment was applied to 216 pigs (6/pen; 2/pen/HI). This was followed by transportation for 1 h on a livestock trailer at the end of which pigs were subjected to a final handling procedure. Blood samples (to measure acid-base, cortisol, and catecholamine levels) were collected and rectal temperature was measured 2 h before (baseline) the HI treatment and after the final handling procedure (final). Feeding RAC (5 and 7.5 mg/kg) improved (P < 0.01) ADG (9.9 and 9.0% for 5 and 7.5 mg/kg RAC, respectively) and G:F (8.8 and 11.8%, respectively) compared to controls, with no differences (P > 0.05) between the 2 RAC levels. Increasing the intensity of handling decreased (P < 0.001) final blood pH, bicarbonate, and base excess and increased (P < 0.001) final plasma cortisol and norepinephrine levels. Aggressive compared to Gentle handling increased (P < 0.05) the incidence of pigs exhibiting open-mouth breathing and skin discoloration after the final handling procedure but had no effect (P > 0.05) on the incidence on non-ambulatory, non-injured pigs. There was no effect (P > 0.05) of feeding RAC on final rectal temperature or blood-acid base measurements. Feeding 7.5, but not 5.0, compared to 0 mg/kg RAC increased (P < 0.05) final plasma epinephrine levels and the incidence of non-ambulatory, non-injured pigs. This study confirms the improved growth performance of pigs fed RAC and the negative effects of aggressive handling on physical, metabolic, and physiological responses of pigs. It also suggests that pigs fed 5 compared to 0 mg/kg RAC showed similar responses to transport and handling. However, pigs fed 7.5 mg/kg of RAC had a greater incidence of non-ambulatory, non-injured pigs when subjected to the handling / transport model used in this study and this warrants further research.