A diet fortified with L-lysine and L-arginine reduces plasma cortisol and blocks anxiogenic response to transportation in pigs.

We studied the effects of diet fortified with L-lysine HCl (Lys) and L-arginine (Arg) on stress (transportation) responses in male finishing pigs (Landrace x LargeWhite x Duroc). Pigs (n = 16) were randomly divided into two equally sized groups so that the average starting body weight in the groups was identical. For 1 week immediately preceding the transportation, the first group of pigs received a control diet while the second group received a Lys and Arg fortified diet. Plasma aminogram, cortisol and body weight were evaluated. Behavior of pigs was measured with the help of a video camera, recorded for 2 h at the same time, as on the day, before a day and immediately after transportation. The study revealed main stimulatory effects of transportation and main inhibitory effect of Lys and Arg on plasma cortisol (P < 0.05) without transportation x treatment interactions. Pigs fed with Lys and Arg diet tend to have higher body weight at the end of the experiment, when compared to their normally fed counterparts, but the difference did not reach a significant level (P < 0.21). Lys and Arg diet significantly inhibited stress-induced increase in locomotion (P < 0.05), without affecting feeding pattern. Transportation stress decreased plasma Lys and Arg. This decrease was reversed in the fortified group, and what is more the plasma Lys and Arg levels were significantly higher than in controls (P < 0.05). Lys and Arg enhanced plasma urea production (P < 0.05), without regards to stress. The behavioral results indicate a reduction in stress-induced anxiety in pigs fed with Lys and Arg fortified diet, that parallels similar observations in research with rats and broilers. The mechanism probably involves a decreased plasma cortisol, and/or normalized plasma Lys, Arg levels.