Effects of feeding free or microencapsulated gluconic acid on growth performance of weanling pigs

Organic acids belong to the supplements that can be used as an alternative to antibiotics fed to farm animals as growth promoters. Gluconic acid (GA) has been shown to reach the large intestine in rats where it can be fermented by the microflora (1). In piglets, when GA was fed at 0.3 and 0.6%, average daily gain of the animals was improved (2). Aim of this study was the evaluation of the effect of feeding GA in its free form or microencapsulated on piglet growth and intestinal microflora. Methods: Immediately after weaning, 48 piglets were divided into 3 groups (16 animals per group, housed in individual cages) for a 32 d trial. Treatments were a commercial diet with a) no addition (control diet) or with b) 0.3% of microencapsulated GA (MGA), and c) 0.3% of free GA (FGA). Feed and water were provided ad libitum. Animals were weighed every week and feed consumption was recorded. At the end of the trial, 8 animals per group were killed. Samples of jejunum and caecum content were cultured for viable bacteria (coliforms, clostridia, enterococci, and lactobacilli) and the content and the mucosa from the middle section of the jejunum and from ileum and cecum were sampled for pH, ammonia and SCFA determination, and for intestinal mucosa morphology analysis. Results: Feeding GA did not influence live weight, average daily gain (ADG), and daily feed intake of piglets. Feed to gain ratio (FG) was improved by GA between Day 14 and 21 (1.68, 1.44, and 1.34 for control, MGA, and FGA, respectively; P < 0.05) but differences were not significant in the period 0-32 d (Table 1). Intestinal counts of viable bacteria were not significantly influenced by treatment. Nevertheless, caecal clostridia showed a tendency towards a reduction when GA was fed (6.9, 6.4, and 6.2 log10 CFU/g for control, MGA, and FGA, respectively). Ammonia concentration in the caecum was higher when MGA was fed (P < 0.01). Compared with control, feeding MGA reduced the concentration of iso-butyric acid in jejunum and ileum (P < 0.10) but no other differences in SCFA intestinal concentrations were observed. Animals receiving the FGA diet had longer ileal villi (+ 18%; P < 0.10) and shorter caecal crypts ( 17%; P < 0.05) than control animals. Conclusion: Despite the fact that during a previous study GA had improved piglets growth performances (2), both the free and the microencapsulated form of GA failed to enhance animal growth. Further studies will be needed to achieve a deeper understanding of the effect that GA has on growth and intestinal ecology and morphology of piglets. 1) ASANO, T, YUASA, K, YOSHIMURA, Y, TAKENAWA, S and FUKUBA, H (1997): J. Jpn. Soc. Nutr. Food Sci. 50, 287-294. 2) BIAGI, G., PIVA, A., MOSCHINI, M., VEZZALI, E., and ROTH, F. X. (2005): J. Anim. Sci. Accepted for publication.