Comparison of medium chain organic acids with zinc oxide and benzoic acid; effect on growth performance of pigs

Medium chain organic acids (MCOA) show strong and specific antimicrobial activity and may be useful as part of an antibiotic reduction strategy. Two trials were conducted to evaluate the effect of MCOA on growth performance of pigs in comparison with benzoic acid (BA) and ZnO (ZnO). Each used 240 pigs in a randomised complete block design with six treatments in eight replicate pens. Trial 1 tested a blend of C6:0, C8:0, C10:0 and C12:0 for 56 d post-weaning. Treatments were (1) control basal diet (BD), (2) BD+ZnO (3) BD+ZnO+BA, (4) BD+MCOA (5) BD+MCOA+ZnO, (6) BD+MCOA+BA. Pigs receiving MCOA+BA showed higher average daily liveweight gain in the grower period (849 g/d) than pigs receiving the control diet (773 g/d) or the ZnO treatment (779 g/d; P=0.040), grew 7% more efficiently (P=0.008) and were 3.02 kg heavier at 56 d than control pigs. Trial 2 tested the MCOA blend at two inclusion levels in comparison with C6:0/C12:0 (50/50) and C6:0/C12 monolaurin (C12M; 50/50), for 28 d post-weaning. Treatments were (1) control basal diet, (2) BD+ZnO (3) BD+1,500 mg/kg MCOA (4) BD+750 mg/kg MCOA (5) BD+ C6/C12 (total 3,000 mg/kg), (6) BD + C6/C12M (total 3,000 mg/kg). Pigs receiving 750 mg/kg MCOA grew more slowly than those receiving C6/C12M or ZnO (P<0.05) to d 21. Pigs fed ZnO were 1.61 kg heavier than these pigs (P<0.05), while those fed C6/C12M were 1.29 kg heavier (P<0.05) at d 21. During 0-14 d pigs fed ZnO showed the best feed conversion ratio (FCR), but at 15-28 d the improvement was no longer seen. Both the C6/C12 and the C6/C12M treatments appeared to improve FCR during this second phase (P<0.01). The results suggested that supplementation with a combination of MCOA and BA may be a promising strategy to improve growth performance while replacing ZnO and reducing antibiotic dependence.