Effects of dietary hop β-acids or colistin on the performance, nutrient digestibility, and intestinal health of weanling pigs

The purpose of this study was to evaluate the effects of dietary graded levels of hop (Humulus lupulus) β-acids or colistin on the growth performance, nutrient and energy digestibility, diarrhea occurrence, unthrifty pigs, blood respiratory burst, organ weights, small intestine histology, and intestinal microbial diversity of weanling pigs, as well as in vitro bacterial sensitivity to hop β-acids. Two hundred 21-d weaned castrated male and female pigs (6.2±0.33kg initial BW) were used in a randomized complete block design experiment with 5 treatments, 8 replicates, and 5 pigs per experimental unit (pen). Pigs were fed corn-soybean meal basal diets supplemented with 0 (negative control), 120, 240, or 360mg/kg hop β-acids, or with 40mg/kg colistin (antimicrobial control) during a 35-d nursery feeding experiment. On d 7 and 35 of the experiment, one castrated male from each pen was slaughtered to evaluate organ weights, small intestine histology, and intestinal microbial diversity. ANOVA and orthogonal contrasts were performed to determine the dose-response of each variable to dietary hop β-acids levels (0, 120, 240, and 360mg/kg), as well as to compare the means of antimicrobial control with the negative control and with each dietary hop β-acids level. Increasing dietary levels of hop β-acids improved linearly (P<0.05) BW, ADG, G:F, and digestibility of ether extract of feed of weanling pigs. The colistin treatment improved (P<0.03) BW, ADG, and G:F compared to the negative control but did not affect nutrient and energy digestibility. No difference in growth performance was observed between hop β-acids (120, 240, or 360mg/kg) and colistin. No effect on ADFI was observed. Overall, the occurrence of diarrhea was lower (P<0.01) for colistin, negative control, and 360mg/kg hop β-acids than for 120 and 240mg/kg hop β-acids, while no unthrifty pigs were identified throughout the entire experimental period. No effect of dietary treatments on blood respiratory burst, organ weights, small intestine histology, and intestinal microbial diversity was observed. By using the standardized paper disk diffusion method, Staphylococcus aureus was sensitive to hop β-acids (33.1±2.57mm inhibition zone), while Escherichia coli, Salmonella enteritidis, Salmonella typhimurim, and Enterococcus faecalis were resistant. In conclusion, dietary hop β-acids concentrations up to 360mg/kg improved weanling pig growth rate by affecting the efficiency of feed utilization, as well as observed for colistin.