Impact of ractopamine hydrochloride on growth performance, carcass and pork quality characteristics, and responses to handling and transport in finishing pigs

The effect of feeding ractopamine hydrochloride (RAC) on growth performance, carcass and pork quality, and blood acid-base and catecholamine responses to handling and transport in finishing pigs was evaluated using a randomized complete block design to compare 2 RAC levels (0 vs. 10 mg/kg). Crossbred pigs (n = 144) were housed in single-sex pens (barrow or gilt) of 3 with 24 pens/RAC level. The study was carried out for a 28-d period from 104.0 +/- 5.99 to 136.7 +/- 6.44 kg BW. At the end of the growth study, pigs were subjected to handling and transport procedures that involved an initial aggressive handling procedure (pigs moved 50 m with 8 shocks from an electric prod) followed by a 30-min transport on a standard livestock trailer at a floor space of 0.46 m(2)/pig followed by a final gentle handling procedure (pigs moved 100 m using sort boards and slap paddles). A blood sample was taken and rectal temperature was measured 2 h before (baseline) and immediately after the final handling procedure (final). Barrows (n = 72) were harvested and carcass and pork quality were measured. Feeding RAC increased (P <= 0.05) ADG (19.6%), ADFI (4.2%), and G:F (14.8%). The increase in plasma epinephrine levels from baseline to final was greater (P <= 0.05) for pigs fed RAC; there was a trend (P <= 0.10) for pigs fed RAC to have greater final blood lactate and to show a greater change from baseline to final in blood bicarbonate, partial pressure of and total carbon dioxide, and oxygen saturation levels. However, there were no differences between treatments for changes from baseline to final in rectal temperature, blood pH and lactate, and plasma norepinephrine levels. The incidence of physical indicators of stress and of nonambulatory, noninjured pigs during the handling and transport procedures was similar for the 0 and 10 mg/kg RAC levels. Final farm BW was 4.1 kg heavier, carcass yield was 1.4 percentage units greater, and LM area was 5.18 cm(2) greater for pigs fed RAC compared to the control (P <= 0.05). Minolta a* and b* values were lower (P <= 0.05) and ultimate pH (0.05 units) and Warner-Bratzler shear force (0.43 kg) were greater (P <= 0.05) for pigs fed 10 compared to 0 mg/kg RAC. These results confirm the substantial improvement from feeding 10 mg/kg RAC in growth performance and carcass yield and suggest relatively limited effects on pork quality and on responses to the handling and transport procedures used in this study.