Dietary Antimicrobials in a Wean-to-Finish Facility

2004 University of Nebraska Extension Swine Day Report. The routine use of growthpromoting antimicrobial feed additives is under increasing pressure worldwide. In response to this pressure, it is important that producers and their advisors understand under what circumstances these additives are likely to be effective or ineffective, allowing for improved decisions regarding their use. An experiment was conducted to examine the routine use of antimicrobial feed additives in a wean-to-finish facility. The weaned pigs used in this experiment were purchased from a source where grow-finish pigs were positive for PRRSV, circovirus-2 and Mycoplasma hyopneumoniae and had a previous history of Actinobacillus pleuropneumoniae (APP) related problems. Experimental treatments were no growth-promoting antimicrobials after the pre-starter diet versus continuous antimicrobial additions from weaning to slaughter and day of weaning replicated in a 2 x 2 factorial. At the end of the nursery phase eight weeks after weaning, pigs fed diets containing antimicrobials were heavier (P < 0.01) with less variation in weight (P < 0.01). There was no effect of treatment on feed conversion efficiency for this eight- week period. Pigs fed diets containing antimicrobials also had less severe diarrhea (P < 0.01) at six weeks post-weaning. During the grow-finish phase, diets meant to contain antimicrobials often assayed for lower antimicrobial content than intended. However, there were no mixing errors such that pigs meant to receive diets with no antimicrobials were offered diets containing antimicrobials or vice versa. Pigs fed diets without antimicrobials grew faster (P < 0.05) with improved feed conversion (P < 0.1) during the grow-finish phase. Overall, there was no effect of dietary antimicrobial addition on pig performance, death loss, or carcass traits. In this experiment, while the weaned pigs were purchased from a source with known health challenges, the pigs remained very healthy, as evidenced by decreasing serum titers for APP and the lack of seroconversion for PRRSV. These results suggest that routine and continuous use of antimicrobial feed additives beyond the nursery stage in a wean-to-finish facility with high-health pigs should be evaluated on a case by case basis.