Interpretative Summary: Review: Effects of Ractopamine Hydrocholoride (Paylean) on welfare indicators for market weight pigs
By: Megan LaFollette
In December 2017, Translational Animal Science published a review article that summarized the effects of various dosages of Ractopamine Hydrochloride (sold as Paylean or Engain) on market weight pig welfare. Ractopamine is fed to pigs to improve feed efficiency and carcass leanness with minimal negative effects on pork quality. Unfortunately, Ractopamine has also been suspected to negatively impact pig welfare. Therefore, a review of the welfare effects of Ractopamine on market weight pigs is necessary.
First, the authors outline a brief history of Ractopamine and early research. In 1999, Ractopamine, whose mode of action is as a β-adrenergic agonist, was initially approved in the United States for doses of 5 to 20 mg/kg. Shortly after its release in the early 2000s, there was an increase in reports of increased non-ambulatory pigs at packing plants. At this point a caution statement was added to the Paylean label and intensive research was started. Over the next 3 years, research was conducted showing that pigs fed Ractopamine at the 20 mg/kg dose and handled aggressively had higher rates of non-ambulation and stress response, as compared to a 5 mg/kg dose or 0 mg/kg. Therefore, for Paylean, the dosage range was reduced to be 5 to 10 mg/kg. However, as long as pigs were handled gently, Ractopamine feeding did not impact non-ambulation rate. This research also showed that overall, regardless of Ractopamine administration, non-ambulatory pigs are in a state of metabolic acidosis.
Review authors outlined numerous additional studies on the effects of Ractopamine on market pig welfare in areas such as mortality, lameness, behavior, and physiology. For mortality, after reviewing studies on over 15,000 pigs in the last 18 to 28 days prior to market, Ractopamine was concluded to have minimal effects on mortality. For lameness, Ractopamine was found to decrease bone mass and strength when fed at doses of 20 mg/kg, but at low doses effects are minimal and can be managed by increasing dietary phosphorus. For behavior, although studies are inconsistent in determining the effects of feeding Ractopamine on activity and aggression in the pen, the majority of studies find that Ractopamine fed pigs are more difficult to handle at doses above 5 mg/kg. Finally, for physiology, feeding pigs Ractopamine may increase some measures of stress (heart rate, epinephrine, cortisol, rectal temperature, blood lactate, blood pH) after handling especially at higher dosages; Ractopamine fed a 10 or 20 mg/kg also increases baseline blood lactate for market weight pigs.
Overall, this review suggests that Ractopamine – especially fed at doses of 5 mg/kg and below – has minimal or inconsistent effects on market weight pig mortality, lameness, home pen behavior, handling difficulty, and rates of non-ambulatory. However, Ractopamine fed at doses above 5 mg/kg may increase difficulty of handling and, when handled aggressively, rates of non-ambulatory market weight pigs. Regardless, the review authors suggest that market weight pig transport losses should be managed by implementing low stress handling and transport practices that also benefit pig welfare.
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