Effect of dietary l-carnitine and ractopamine-hcl (paylean) on the metabolic response to handling in growing-finishing pigs

Two experiments (384 pigs) were conducted to determine the interactive effect of dietary L-carnitine and ractopamine·HCl (Paylean) on the metabolic response to handling. Experiments were arranged as split plots, with handling as the main plot and diet as subplots (4 pens/treatment). Dietary Lcarnitine (0 or 50 ppm) was fed from 85 lb to the end of the trials (260 lb) and Paylean (0 or 20 ppm) was fed for the last 4 wk of each trial. At the end of each trial, two pigs per pen were assigned to one of two handling treatments. Gentle-handled pigs were moved at a moderate pace three times through a 164-ft course and up and down a 15° loading ramp. Nongentle-handled pigs were moved at a faster pace, up and down a 30° ramp, and were shocked by an electrical prod. Blood was collected immediately before and after handling in Exp. 1 and immediately after and 1 h after handling in Exp. 2. Feeding Paylean increased (P<0.01) ADG and F/G, but there was no (P>0.10) effect of L-carnitine on growth performance in either trial. In Exp. 1 and 2, nongentle handling increased (P<0.01) lactate dehydrogenase (LDH), lactate, cortisol, and rectal temperature, and decreased pH. In Exp. 1, a Paylean × handling interaction was observed for pH (P<0.01), temperature (P<0.06), and cortisol (P<0.064). Feeding Paylean decreased pH, increased cortisol, increased temperature, and tended (P<0.09) to increase blood lactate when pigs were non-gentle handled, but not when they were gentle handled. Pigs fed Paylean had increased (P<0.01) LDH compared with that of pigs not fed Paylean. Pigs fed L-carnitine had increased (P<0.03) lactate compared with that of pigs not fed L-carnitine. In Exp. 2, pigs fed Paylean had lower (P<0.02) pH immediately after handling, but pH returned to control levels (P>0.96) by 1 h post-handling. Lactate, LDH, cortisol, and temperature changes from immediately posthandling to 1 h post-handling were not different for pigs fed L-carnitine or Paylean, suggesting that L-carnitine did not decrease recovery time of pigs subjected to non-gentle handling. These results demonstrate the importance of proper handling technique to minimize stressful events during the loading and transporting of pigs, regardless of whether either of these feed additives is being fed. This was evident by the large magnitude of the metabolic changes observed for the handling treatments, whereas in general the magnitude of metabolic changes from the dietary treatments was much smaller. Nonetheless, pigs fed Paylean are more susceptible to stress when handled aggressively, compared with pigs not fed Paylean. Dietary L-carnitine did not alleviate the effects of stress when fed in combination with Paylean.