Interactive effect of ractopamine and dietary fat source on pork quality characteristics of fresh pork chops during simulated retail display

Crossbred pigs (n = 216) were used to test the interactive effect, if any, of ractopamine ( RAC) and dietary fat source on the performance of finishing pigs, pork carcass characteristics, and quality of LM chops during 5 d of simulated retail display (2.6 degrees C and 1,600 lx warm-white fluorescent lighting). Pigs were blocked by BW and allotted randomly to pens (6 pigs/pen), and, after receiving a common diet devoid of RAC for 2 wk, pens within blocks were assigned randomly to 1 of 4 diets in a 2 x 2 factorial arrangement, with 5% fat [beef tallow (BT) vs. soybean oil (SBO)] and RAC (0 vs. 10 mg/kg). Diets were formulated to contain 3.1 g of lysine/Mcal of ME and 3.48 Mcal/kg of ME. Across the entire 35-d trial, pigs fed RAC had greater (P < 0.01) ADG and G: F, but RAC did not affect (P = 0.09) ADFI; however, performance was not affected (P >= 0.07) by dietary fat source. Carcass weight, LM depth, and lean muscle yield were increased (P < 0.01), whereas fat depth was decreased (P = 0.01), in carcasses from RAC-fed pigs; however, carcass composition measures were similar (P >= 0.27) between fat sources. Feeding 10 mg/kg of RAC reduced (P <= 0.04) the proportions of SFA and MUFA and increased (P < 0.01) the proportion of PUFA and the iodine value, in pork backfat. Conversely, backfat from carcasses of BT-fed pigs had greater (P < 0.01) percentages of SFA and MUFA, and lower (P < 0.01) percentages of PUFA, than backfat from SBO-fed pigs. Moreover, the PUFA: SFA and iodine value were considerably reduced (P < 0.01) by including BT in swine finishing diets. The LM from pigs fed RAC had greater pH values (P = 0.03) and received greater ( P <= 0.01) American and Japanese color scores during retail display. The LM from RAC-fed pigs had lower (P <= 0.02) L*, a*, and b* values, whereas the LM of SBO-fed pigs received greater (P < 0.01) subjective color scores and b* values, as well as lower L* values, than the LM of BT-fed pigs. Across the 5-d display period, oxidative rancidity was not affected by dietary RAC (P=0.58) or fat source (P=0.47). Neither RAC nor fat source altered LM cooking losses and shear force values. Feeding 10 mg/kg of RAC will improve rate and efficiency of gain, carcass composition, and LM quality. And, even though fatty acid composition of backfat samples was altered by dietary fat source, performance and carcass composition, as well as quality during 5 d of retail display, were similar when pigs were fed diets formulated with BT or SBO.