Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: April 20, 2008
Publication Date: July 7, 2008
Citation: Poletto, R., Garner, J.P., Cheng, H., Marchant Forde, J.N. 2008. The effects of ractopamine, gender and social rank on aggression and peripheral monoamine levels in finishing pigs. Journal of Animal Science. 86(E.Suppl 2):352. Technical Abstract: As of significant importance for swine production, inter-individual aggression has a negative impact in animal productivity and welfare. Moreover, further knowledge of the effects of the feed additive ractopamine (RAC), a ß-adrenergic agonist widely used as swine feed additive, is needed to elucidate its impact on pig welfare. Our aim was to evaluate the effects of a “step-up” RAC feeding program on home pen aggression and peripheral levels of tryptophan (Trp), serotonin (5-HT) and the catecholamines dopamine (DA), norepinephrine (NE) and epinephrine (EP) in finishing pigs. Thirty-two pigs (16 barrows and 16 gilts) were assigned to pens of four (by gender) as either control (CTR) or RAC treatment. Treated animals were fed RAC at 5ppm for 2 weeks, then 10ppm for two more weeks until slaughter. The dominant and subordinate pigs in each pen were determined at assignment by continuous behavior observation (36 h) according to the proportion of encounters that each individual won or lost. To evaluate aggressive interactions (number of bites (B), head knock (HK), pursuit (P)) in the home pen, behavior was continuously recorded 1x/wk (0800 h to 1100 h) for five weeks. Recordings were carried out at d-2 (baseline), d5, 12, 19 and 26 of the experiment. Blood samples were collected from each animal 1x/wk for five weeks, starting on the week prior to dietary treatment following until the end of experiment (d -3, 4, 11, 18 and 25). Levels of Trp and 5-HT in whole blood and DA, NE and EP in plasma were measured using electrochemical high-performance liquid chromatography (HPLC). A 2 × 2 × 2 factorial analysis with treatments, gender and social rank, and their interactions was computed with repeated mixed models using individuals as units. Gilts showed significantly more average B (1.72±0.24 vs. 0.92±0.22) per interaction compared to barrows. Compared to baseline RAC-fed gilts increased B while others decreased (p<0.05). CTL barrows showed the lowest number of HK (0.36±0.14), with others showing very similar counts (0.75±0.14, treatment×gender, p<0.05). In relation to baseline, levels of P increased greatly in RAC-fed gilts, but decreased for RAC-fed barrows and CTL animals (treatment×gender, p< 0.01). Overall, gilts had a higher average of total actions per aggressive interaction than barrows (2.5±0.24 vs. 1.49±0.22, p<0.01) and RAC-fed gilts had a significant increase in the total number actions performed (p < 0.01). Dominant RAC-fed animals had highest concentrations of NE (p<0.05), and dominant barrows had higher EP levels than subordinate ones (p<0.05), but were similar in gilts regardless of social status. Moreover, RAC-fed gilts had lower 5-HT compared to RAC-fed barrows (treatment × gender, p=0.08). Overall, Trp and 5-HT levels increased up to d11 and plateau until the end of the experiment (day, p<0.001). Gilts, specially when fed RAC, showed more aggressive behavior which may be linked to lower 5-HT availability, leading to increased production costs and impairment of welfare.