In-Feed Antibiotics Elicit Intestinal Integrity Modifications Early In Post-Weaning Life

Abstract The physiological mechanisms by which in-feed antibiotics improve pig growth performance are largely unknown. One proposed mode of action is improvements in intestinal integrity and function. Therefore, the objective of this study was to test the hypothesis that in-feed therapeutic and sub-therapeutic antibiotics would improve intestinal integrity and function in nursery pigs. Twenty-four weaned pigs (6.1±1.1 kg BW) were randomly allotted to individual pens and assigned one of three dietary treatments as follows (n = 8 pigs/trt): 1) control, no antibiotics (CON), 2) CON + sub-therapeutic chlortetracycline [40 ppm in feed (sCTC)], and 3) CON + chlortetracycline-tiamulin [400 ppm + 35 ppm, respectively (CTCDen)]. The study consisted of two consecutive 14 d phases. Chlortetracycline-tiamulin was only fed in phase 1, sCTC was fed in both phases. Phase 1 and 2 ADG, ADFI, and G:F were determined. After 28 d, ileal and colonic ex vivo intestinal integrity was assessed via transepithelial resistance (TER) and macromolecule flux (FD4) in modified Ussing chambers. All data were analyzed for the fixed effects of treatment and start BW as a covariate. In phase 1, compared with CON and sCTC, CTCDen tended to have greater ADG (0.28, 0.31, and 0.33 kg/d, respectively, P = 0.10) and ADFI (0.28, 0.30, and 0.35 kg/d, respectively, P = 0.09). No differences in phase 1 G:F were observed (P = 0.11). Phase 2 ADG, ADFI, and G:F did not differ (P > 0.10). Further, ileal TER and FD4 did not differ (P > 0.10). Colonic TER tended to be increased in sCTC compared with CON and CTCDen (78, 56, and 59 Ω/cm2, respectively, P = 0.07). Compared with CON, colonic FD4 flux was decreased in sCTC and CTCDen by 35–40% (P = 0.03). Altogether, these data indicate that in-feed antibiotics improve colon integrity early in production which may contribute to improved growth performance.