Stress susceptibility in pigs supplemented with ractopamine1

Abstract

Ractopamine is a β-adrenergic agonist used as an energy repartitioning agent in the diets of finishing pigs. Most ractopamine studies are limited to evaluations of growth performance and meat quality, and there is little information on the effects of this additive on the behavior and welfare of pigs. Therefore, the objective of this study was to evaluate various indicators of stress caused by feeding diets containing ractopamine. One hundred seventy barrows and 170 gilts weighing 107.3 kg were allocated to 30 pens with 10 to 12 barrows or gilts per pen. Pigs were offered 1 of the 3 dietary treatments (0, 5, or 10 mg ractopamine/kg) for 28 d with 5 barrow pens and 5 gilt pens per treatment. Pigs were evaluated for behavior 3 d per week 1 wk before the initiation of the experiment and throughout the experiment. Each pig was classified into 1 of the 13 activities (drinking water, lying alone, lying in clusters, standing, nosing pig, sitting, feeding, biting pig, walking, exploring, running away, playing, and mounting pen mates) and also grouped into 1 of the 3 categories (calm, moving, and feeding themselves) based on those activities. At the end of the experiment, 3 pigs from each pen were slaughtered, and blood samples were collected during exsanguination to determine physiological indicators of stress (cortisol, lactate, and creatine-kinase enzymes). The incidence of skin and carcass lesions was determined at shoulder, loin, and ham. Ractopamine had no effect (P > 0.05) on pig behavior, total number of skin and carcass lesions, or blood concentrations of cortisol or lactate. However, there was an increase (P < 0.05) of creatine kinase concentrations in pigs receiving ractopamine-supplemented feed. This finding is consistent with the concept that ractopamine may cause muscular disorders, and this warrants further investigation.

Review: Effects of Ractopamine Hydrochloride (Paylean) on welfare indicators for market weight pigs1

“…However, the effects of RAC on fighting may have been minor as this did not result in greater carcass damage scores at the plant. The results of Rocha et al (2013) align with a previous study that reported no effects of RAC on skin/carcass lesions ( Athayde et al, 2013 ). Lastly, other studies designed to measure the impact of RAC on general behaviors reported minimal RAC effects on agonistic behaviors ( Schaefer et al, 1992 ; Marchant-Forde et al, 2003 ).…”

“…The RAC effects on cortisol concentrations during baseline, post-handling, post-transport, and exsanguination are summarized in Table 15 . These studies indicate that RAC had no effect on baseline cortisol values at 5 and 7.5 mg/kg ( Peterson et al, 2015 ), 10 mg/kg ( Marchant-Forde et al, 2003 ), or 20 mg/kg ( James et al, 2013 ; Study #1) for feeding durations of 28 d. Likewise, 3 studies reported no effects of feeding 5 mg/kg ( Athayde et al, 2013 ), 7.5 mg/kg ( Rocha et al, 2013 ), or 10 mg/kg ( Marchant-Forde et al, 2003 ; Athayde et al, 2013 ) on either plasma or urinary cortisol values measured at post-transportation or exsanguination. The effects of RAC on post-handling cortisol values are inconsistent in the literature.…”

“…In addition, these authors reported no RAC effect on abnormal, stereotypic, or agonistic behaviors. Similarly, Athayde et al (2013) reported no effect of 5 or 10 mg/kg RAC on calm (lying, sitting, or standing), moving, or feeding behaviors. In response to a novel handler entering pig home pens, Benjamin et al (2006) reported no difference in latency to approach handlers for market weight pigs fed 0 or 10 mg/kg RAC.…”

“…These studies demonstrate that RAC had no effects on post-handling blood lactate or pH values when fed at 5 or 7.5 mg/kg ( Puls et al, 2013 ; Peterson et al, 2015 ). Ractopamine also had no effects on blood lactate and pH values measured at stunning/exsanguination when fed at 5 mg/kg ( Gillis et al, 2007 ; Athayde et al, 2013 ) and 7.5 mg/kg ( Rocha et al, 2013 ). However, feeding 10 mg/kg of RAC produced conflicting results for blood lactate values measured immediately post-handling ( Puls et al, 2015 ; Noel et al, 2016 ) and at stunning/exsanguination ( Gillis et al, 2007 ; Athayde et al, 2013 ).…”

Metabolic and histologic responses of pacu (Piaractus mesopotamicus) fed diets supplemented with increasing concentrations of ractopamine

“…Therefore, the results of this study indicated that ractopamine can act as a stressor agent culminating in the activation of the hypothalamic-pituitary-interrenal-axis in pacu when the feed is supplemented with β-adrenergic in concentrations higher than 11.25 mg kg −1 and is provided to animals in the finishing phase during 60 days. Similarly, increased circulating cortisol levels were not noted in finishing pigs fed diets containing 10 mg kg −1 or less of ractopamine (Athayde et al, 2013). There are no scientific reports that explain how and why chronic exposure to high concentrations of dietary ractopamine is recognized by the hypothalamus of teleost fish as a stressor agent and, therefore, this warrants further investigation.…”