The effects of steam conditioning and antimicrobial inclusion on feed manufacturing and inactivation of Enterococcus faecium, a Salmonella surrogate

Animal well-being, evolving feed manufacturing regulations, human health, and consumer perception drive the continued need to provide safe feed to food animals. Two experiments were conducted to determine the effects of antimicrobial inclusion and conditioning temperature variations on feed manufacturing metrics (EXP1) and the inactivation of Enterococcus faecium, a Salmonella surrogate (EXP2). Both short-term (ST) and long-term (LT) steam conditioning techniques were utilized in this split-plot design where ST (10 s) or LT (60 s) steam conditioning served as whole plot units. Whole plots contained either 2 × 3 (EXP1) or 2 × 4 (EXP2) factorial arrangements varying in mixer-added antimicrobial inclusion (with or without) and degree of thermal processing (unprocessed mash, 71°C, 82°C, and 88°C). Manufacturing of dietary treatments was replicated 3 times. A basal diet was used to obtain desired conditioning temperature before Salmonella surrogate-inoculated feed was exposed to either ST or LT conditioning. In EXP1, conditioning time and antimicrobial inclusion interacted (P = 0.03) by decreasing pellet durability when antimicrobial was included in diets subjected to ST conditioning. Pellet durability was not affected when LT conditioning was utilized. In EXP2, conditioning time, antimicrobial inclusion, and degree of thermal processing interacted (P < 0.0001) to inactivate the Salmonella surrogate using ST conditioning at 71°C. Further inactivation from higher ST and LT conditioning temperatures, with and without antimicrobial, was apparent. Within the parameters of this study, both ST and LT steam conditioning resulted in 3 and 4-log reductions of the Salmonella surrogate, respectively. However, degree of bacterial inactivation and pellet quality are dependent on manufacturing and antimicrobial additive strategies.