Growth performance, carcass characteristics, physiological and gut health effects of feeding diets containing bacitracin methylene disalicylate (BMD) to heat-stressed finishing pigs.

Abstract

Heat stress affects pig growth performance, carcass composition, and immune status. The present study was conducted to evaluate the effects of heat stress and adding bacitracin methylene disalicylate (BMD, 30g/ton) to a 10% DDGS commercial diet on growth performance, carcass characteristics, physiological parameters, small intestine morphology, and hindgut volatile fatty acid (VFA) production of finishing pigs. Four groups of 32 finishing pigs (n = 128) with initial BW between 80 to 90 kg were used in this study. Pigs were randomly assigned to diets and environmental temperature treatments in a 2 x 2 factorial arrangement. Pigs were fed a control (CON) or BMD (30g/ton) diet and exposed to a constant thermal neutral temperature (23°C) or cyclical heat stress conditions (37°C from 10:00 to 19:00 and 27°C from 19:00 to 10:00) in environmental chambers for a 28-d experimental period. Pigs housed under heat stress conditions had significantly lower average daily gain (ADG, P < 0.0001), average daily feed intake (ADFI, P < 0.0001), gain:feed (G:F, P < 0.001), and higher average daily water intake (ADWI, P = 0.03), compared with pigs housed in the thermoneutral environment. Supplementation of BMD in the diet did not improve growth performance of pigs. Average daily gain tended (P = 0.07) to be lower for pigs fed the BMD diet, while ADFI, G:F, and ADWI were not affected by dietary treatment. Carcass characteristics did not differ between dietary treatments. However, pigs assigned to the heat stress environment had lower live BW (P < 0.0001) and lower hot carcass weight (P < 0.0001) than pigs housed in the thermal neutral environment. Dressing %, 10th rib back fat depth, loin eye area, and lean % were not affected by temperature treatment. Saliva cortisol concentration did not differ between dietary treatments during the experimental period, but the initial level was lower (P < 0.05) for pigs fed the BMD diet. Heat stress led to an increased (P < 0.05) level of saliva cortisol on d 1, but no effects were observed on the following days. Serum haptoglobin concentration was not different between dietary treatments, while heat stressed pigs showed a higher (P < 0.05) level of haptoglobin on d 1, and levels tended to remain higher (P < 0.1) on d 13 of heat stress. Cytokines IL-1β and TNF-α were not affected by heat stress, but pigs fed the BMD diet had an initial lower (P < 0.0001) level of serum IL-1β, and tended to be lower (P < 0.1) on d 13 of heat stress as compared to pigs fed CON. Small intestine morphology was not affected by temperature treatment, but pigs fed the BMD diet tended to have greater (P = 0.07) villi height at duodenum, and greater crypt depth at duodenum (P = 0.09) and jejunum (P = 0.07), respectively. Dietary treatment did not affect VFA production in the cecum, while pigs housed under heat stress conditions tended to have less propionate (P = 0.08) concentration, greater A:P ratio (P = 0.08), and significantly less valerate (P = 0.02) produced in the cecum compared with pigs under the thermoneutral environment.