The Effects of Ractopamine on Behavior and Physiology of Finishing Pigs

Purdue University 2002 Swine Research Report. The feed additive ractopamine, a beta-adrenergic agonist, acts as a repartitioning agent, promoting lean tissue deposition in market-weight pigs (Watkins et al., 1990; Crome et al., 1996). It has been the focus of widespread research over the last 20 years and has been shown to give substantial improvements in average daily gain, feed conversion efficiency, dressing percent and carcass lean content (Watkins et al., 1990; Gu et al., 1991a,b; Uttaro et al., 1993; Crome et al., 1996). Its usage may also confer environmental benefits such as reduced manure volume, decreased ammonia and volatile fatty acids emissions from slurry (Sutton et al., 2001). It was formally approved for use in swine in the US in 1999, and subsequently, a number of other countries. Research has also shown that the production advantages of ractopamine are relatively brief. Performance measures peak and then decline (Bark et al., 1992; Williams et al., 1994) with the greatest response occurring during the first 14 days (Williams et al., 1994). In recent studies, pigs fed a constant level of ractopamine had slower growth rates and poorer feed conversion efficiency than control pigs by the fifth week on test (Herr et al., 2002a, 2002b). At a cellular level, the change in response may be due to a combination of down regulation of the -adrenergic receptors and ractopamines partial agonist activity (Liu et al., 1994; Mills, 2001). The little behavioral research carried out to date has confirmed that after 6 weeks of being fed ractopamine, pigs spent more time lying down and less time walking (Schaefer et al., 1992), but there was no evidence of decreased joint soundness and there is no scientific evidence of behavioral or physiological responses to stress. As global usage increases, it is important that these concerns are addressed. The objectives of this study, therefore, were to examine the behavior and physiology of marketweight pigs during the conventional ractopamine administration period and in response to stressors encountered during routine handling, weighing and during transport.