Three experiments were carried out in order to determine the potential of silver nanoparticles as an additive in diets for weanling pigs. In Experiment 1, ileal contents of 4 pigs weaned 7 days before were incubated in vitro for 4h at 37◦C with 0, 25, 50 and 100 µg Ag/g. Metallic silver (in colloidal form) linearly reduced coliforms (P=0.003) and lactobacilli (P=0.041) concentration, but did not affect the lactobacilli proportion compared with the control. In Experiment 2, three groups of 5 weaned pigs were given a diet with 0, 20 or 40 µg Ag/kg. The second week after weaning daily growth of pigs increased linearly (P=0.007) with the dose of silver nanoparticles. A trend (P=0.073) for a linear reduction in the ileal concentration of coliforms was observed by culture counts, but lactobacilli remained unaffected. There were no differences among treatments in the ileal concentration of coliforms or lactobacilli measured by FISH. However, the concentration of total bacteria (P=0.010) and Atopobium (P=0.001) decreased at a decreasing rate. No differences were detected in the other bacterial groups tested, except for a lowest concentration of the Clostridium perfringens/ Clostridium histolyticum group in 20 µg Ag/kg (P=0.012). No treatment effect was detected in histological examination of ileal mucosa. In Experiment 3, productive performance and silver retention in tissues with 0, 20 or 40 µg Ag/kg diet were studied with 6 lots of 4 piglets per treatment in five weeks after weaning. Although previous results indicate that low doses of metallic silver nanoparticles given as dietary additive could improve intake and growth of weanling piglets, Experiment 3 do not allow to clearly stating this. Silver retention in tissues is only appreciated at low levels in the livers of piglets, whereas it was not detected in kidneys or in skeletal muscles.
It is concluded that silver effect may be mediated through its antimicrobial properties, either by acting against certain bacterial groups or just reducing the microbial load of the small intestine; however, other beneficial effects over the host metabolism cannot be discarded.
M Fondevila, R Herrer, MC Casallas, L Abecia, JJ. Ducha, 2009. Animal Feed Science and Technology 150: 259–269.