Effects of ractopamine level on the growth performance, carcass and meat quality, and blood acid-base and catecholamine responses to handling and transport procedures in finishing pigs

Abstract Text:

This study was carried out to evaluate the effect of feeding ractopamine (RAC) on growth performance, carcass and meat quality, and blood acid-base and catecholamine responses to handling and transport in finishing pigs.  The study used a RCBD with 2 RAC levels (0 vs. 10 mg/kg) and involved 144 crossbred pigs housed in single-gender pens (barrows or gilts) of 3 pigs with 24 pens/RAC level.  The study was carried out over a 28-d period from initial BW 104.0 ± 5.99 kg to final BW of 142.8 ± 8.66 kg.  Diets were formulated to meet the requirements of pigs fed 10 mg/kg RAC.  Feed and water were available ad libitum.  At the end of the growth study, pigs were subjected to handling and transport procedures.  The handling model involved an initial aggressive handling procedure (pigs moved a distance of 50 m with 8 shocks from an electric prod), followed by 30 min transport on a standard livestock trailer at a floor space of 0.46 m²/pig, after which pigs were subjected to a final gentle handling procedure (pigs moved a distance of 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).  Pigs were harvested and carcass and meat quality were measured.  Feeding RAC increased (P < 0.05) ADG (19.6%), ADFI (4.2%), G:F (14.8%), and carcass yield (1.4% units).  Minolta a* and b* 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.  The increase in plasma epinephrine levels from baseline to final was greater (P < 0.05) for pigs fed RAC, however, there were no differences (P > 0.05) between treatments for changes in rectal temperatures, or plasma acid-base and norepinephrine levels from baseline to final.  In addition, the incidence of non-ambulatory, non-injured pigs during the handling and transport procedures was similar (P> 0.05) for the 0 and 10 mg/kg RAC treatments (2.8 vs. 1.4%, respectively).  The results of this study confirm the substantial improvement in growth performance and carcass measures from feeding RAC at 10 ppm and suggest relatively limited effects of feeding this level of RAC on pork quality and responses to handling and transport.

Keywords: handling, pigs, ractopamine