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Diet modifications to improve finishing pig growth performance and pork quality attributes during periods of heat stress^1,2

^* Department of Animal Sciences, University of Missouri, Columbia 65211

⁴ Correspondence: Lab 111 Animal Science Research Center (phone: 573-882-7726; fax: 573-884-6093; e-mail: AlleeG{at}missouri.edu).

A total of 196 barrows (88 kg) were used in a 2 x 2 factorial arrangement of treatments and housed in a facility (seven pigs per pen) where temperatures cycled between 27 and 35°C. Treatments consisted of (as-fed basis) two CP levels (13.6 or 11.3%) and two levels of added fat (1 or 8%). Diets were formulated to the same true digestible lysine:ME ratio (1.68 g of lysine/Mcal of ME). Diets were fed and growth variables were measured until pigs reached 114 kg of BW. Ham and LM (loin) 24-h pH (PH24), and light reflectance (CIE L*, and a*, and b*, and hue angle) were taken after slaughter. Additionally, loins were removed and measured for i.m. fat, moisture, glycolytic potential, and subjected to a 7-d retail display evaluation that measured pH, light reflectance, and subjective color and odor score. The remaining boneless lumbar loin segment was vacuum-sealed for 14 d and subsequently measured for pH, light reflectance, and color. Pigs fed the high-CP, low-fat diet had a lower ADG than all other treatments (P = 0.06). High-fat feeding resulted in improved ADG (CP x Fat; P = 0.06) and G:F (Fat effect; P < 0.01). Higher fat and lower protein levels both increased final BF (P = 0.07). Pigs fed the low-CP diets had lower ham PH24 (P < 0.01). Loin PH24 was higher with high fat feeding (P = 0.10). Additionally, pigs fed high fat diets had lower L* values on the ham face and cut loin 24 h after slaughter (Fat effect; P 0.02). These loin color differences were maintained through the 7-d retail display and 14-d storage period. There were no differences in loin i.m. fat or moisture content; however, high-fat feeding tended to decrease loin glycolytic potential (P = 0.11). These results suggest that in a hot environment, decreased CP content improved finishing pig ADG when dietary fat supplementation was low. High dietary fat inclusion during heat stress improved ADG and G:F, especially when CP level was elevated. High-fat diets fed in a hot environment increased pork color intensity by decreasing the glycolytic potential at slaughter and elevating muscle pH.

Key Words: Heat Stress • Pigs • Pork Quality