THE EFFECTS OF RACTOPAMINE ON BEHAVIOR AND PHYSIOLOGY OF FINISHING PIGS

Authors: Marchant, Jeremy; Lay Jr, Donald; PAJOR, E - PURDUE UNIVERSITY; RICHERT, B - PURDUE UNIVERSITY; SCHINCKEL, A - PURDUE UNIVERSITY

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2002
Publication Date: 2/1/2003
Citation: MARCHANT FORDE, J.N., LAY JR, D.C., PAJOR, E.A., RICHERT, B.T., SCHINCKEL, A.P. THE EFFECTS OF RACTOPAMINE ON BEHAVIOR AND PHYSIOLOGY OF FINISHING PIGS. JOURNAL OF ANIMAL SCIENCE. 2003. V 81. P. 416-422.

Interpretive Summary: Since gaining FDA approval in 1999, ractopamine has been increasingly fed to finishing pigs as a repartitioning agent - that is, a compound that promotes deposition of lean tissue at the expense of fat. Whereas ractopamine has been shown to give substantial improvements in weight gain and lean tissue growth, it has also been accompanied by unsubstantiated, anecdotal reports of effects on the behavior of the pigs, making them 'hyperactive' and more susceptible to transport stress. If proven, this will have undoubted implications for the animals' well-being. Our aims therefore, were to examine the behavior and physiology of finishing pigs during the conventional ractopamine administration period and in response to stressors encountered during routine handling, weighing and during transport. We monitored 24h behavior over the course of 4 weeks and also measured behavior during routine handling and weighing at weekly intervals. We took blood samples and recorded heart rate in the home pen and in response to transportation. We found that there were differences in 24h behavioral time budgets, with the ractopamine-fed pigs being more active and alert and taking longer to lie down after being disturbed. However, these differences were only apparent during the first 2 weeks. In contrast, ractopamine pigs remained more difficult to handle over the entire 4-week period. At the end of the 4-week period, they also had higher heart rates than control-fed pigs and higher levels of circulating stress hormones. We conclude therefore, that feeding ractopamine to pigs does affect behavior and physiology. Pigs that are more difficult to move are more likely to be subjected to rough handling and increased stress during transportation, implying reduced welfare, increased workload for the handlers and, potentially, poorer meat quality. However, for this conclusion to be applicable to the finishing pig population in general, other genetic lines should be tested.

Technical Abstract: The objectives of this study were to examine the effects of ractopamine (RAC) on behavior and physiology of pigs during handling and transport. Twenty-four groups of 3 gilts were randomly assigned to one of two treatments, four weeks prior to slaughter; 1) finishing feed plus RAC (10 ppm), 2) finishing feed alone. Pigs were housed in the same building in adjacent pens, with fully slatted floors and access to feed and water ad libitum. Behavioral time budgets were determined in 6 pens per treatment over a single 24-hour period during each week. Behavioral responses of these pigs to routine handling and weighing were determined at the start of the trial and at the end of each week. Heart-rate responses to unfamiliar human presence were measured in all pigs and blood samples were taken from a single pig in each pen on different days during week 4. At the end of week 4, all pigs were transported for 22 minutes to processing. Heart rate was recorded from at least one pig per pen during transport and a further post-mortem blood sample was taken from those pigs that were previously sampled. During weeks 1 and 2, RAC pigs spent more time active (P<0.05), more time alert (P<0.05) and less time lying in lateral recumbency (P<0.05). They also spent more time at the feeder in week 1 (P<0.05). At the start of the trial, there were no differences in behavioral responses to handling. However, over each of the next 4 weeks, fewer RAC pigs exited the home pen voluntarily, they took longer to remove from the home pen, longer to handle into the weighing scale and needed more pats, slaps and pushes from the handler to enter the scales. At the end of week 4, RAC pigs had higher heart rates in the presence of an unfamiliar human (P<0.05) and during transport (P<0.05), but not during loading and unloading. Also at the end of week 4, RAC pigs had higher circulating catecholamine concentrations (P<0.05) than control pigs. Circulating cortisol concentrations and cortisol responses to transport did not differ between treatments. The results show that ractopamine does affect the behavior, heart rate and catecholamine profile of finishing pigs and making them more difficult to handle and potentially more susceptible to handling and transport stress.