Performance of growing-finishing pigs fed medium- or high-fibre diets supplemented with avilamycin, formic acid or formic acid-sorbate blend

A total of 160 growing-finishing pigs with initial body weights of 27 kg and originating from eight farms were used in a performance trial to investigate the effects of dietary fibre content (medium or high) and growth-promoting feed additives (none, avilamycin, formic acid or formic acid-sorbate blend) on pig growth, the feed to gain ratio and the incidence of diarrhoea. Medium-fibre grower and finisher diets [188 and 196 g neutral detergent fibre (NDF)/kg dry matter (DM)] were composed of barley and soybean meal and the respective high-fibre diets (239 and 284 g NDF/kg DM) of barley, oats, barley fibre, peas, soybean meal and vegetable oil. Both medium- and high-fibre diets were similar in net energy (8.7 MJ/kg) and ileal digestible lysine content (8.0 and 6.6 g/kg for grower and finisher diets, respectively). Avilamycin (40 mg/kg) was added to grower diets only whereas formic acid (8 g/kg) and formic acid-sorbate blend (8 g/kg formic acid and 0.4 g/kg potassium sorbate) were added to both grower and finisher diets. No diet X additive interactions were observed in the performance or carcass characteristics of pigs. Dietary fibre content did not affect the growth or feed to gain ratio of pigs. In the growing period, pigs fed diets with avilamycin, formic acid or formic acid-sorbate blend grew faster and had a lower feed to gain ratio than did those fed diets without additives. The differences between the additives were not significant. In the finishing period, pigs fed acidified diets grew faster and utilised feed more efficiently than did those in the avilamycin group. Furthermore, formic acid-sorbate blend enhanced pig performance more than did plain formic acid. For the total fattening period, the average growth rates were 856, 878, 896 and 930 g/day and the feed to gain ratios 2.55, 2.51, 2.43 and 2.32 kg DM/kg gain for diets without additives and with avilamycin, formic acid and formic acid-sorbate blend, respectively. Additives improved the growth and feed to gain ratio compared to diets without additives. Performance was better with organic acid supple mentation of grower and finisher diets than with avilamycin supplementation of grower diet only. In addition, formic acid-sorbate blend improved the feed to gain ratio more than did plain formic acid. In the growing period, additives decreased the incidence of diarrhoea in the medium-fibre diet. In the high-fibre diet, the incidence of diarrhoea was generally low, except in the avilamycin treatment. We concluded that formic acid and formic acid-sorbate blend were equally effective alternatives to the antibiotic avilamycin in grower diets. Since organic acids can be added to finisher diets as well, their use resulted in further improvements in pig performance compared to avilamycin which can be used in grower diets only. The efficacy of formic acid as a growth promoter was intensified with sorbate addition. (C) 2002 Elsevier Science BM All rights reserved.