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Our aim was to evaluate the ability of different strains of Bifidobacteria to cross the gut wall and reach the liver of weaning pigs, and to study the influence of different doses of a probiotic on this parameter. The ability of bacteria to pass from the intestinal lumen to mesenteric lymph nodes and other tissues is called translocation. Several factors promote bacterial translocation, including intestinal bacterial overgrowth, deficiencies in host immune response, and gut barrier damage. Translocation can also be used as a parameter to evaluate a candidate probiotic. Few data are available on the probiotic translocation in weaning pig. We analysed the liver samples from two trials performed with 32 and 64 pigs, respectively, reared from 21 to 35 days of age, fed seven different diets: control diet (C), or C supplemented with one of six different Bifidobacteria strains (1010/CFU/d) (trial 1); or supplemented with four different levels of B. animalis (0, 107, 109, 1011) crossed with 0% or 2% sugar beet fructo-oligosaccharides (trial 2). We found Bifidobacterium spp. genus-specific DNA in liver of subjects from all dietary treatments (control fed pigs included), and no relationship between oral dose and strain appeared. On average 53.1% (trial 1) and 48.4% (trial 2) of the pigs showed the presence of Bifidobacterium spp. genus-specific DNA. We conclude that both endogen and exogenous bacteria can translocate to the liver.

The study addresses the first two weeks of piglet weaning and is aimed at i) identifying new probiotic strains of Bifidobacterium spp. and non-digestible oligosaccharides (NDO) able to increase the level of autochthonous bifidobacteria in the gut, and ii) finding the best probiotic doses, and probiotic-NDO combinations for piglet growth and gut health. Initially, on a total of 60 pigs we administered 12 strains of 4 bifidobacteria species taken from our collection of strains of different ecological origin. We found the most promising probiotic candidates to be two strains of B. animalis subsp. lactis (M 354 and Ra 18) and one strain of B. choerinum (Su 891), as these led to an increase in the number of viable bifidobacteria in the caecum. In a second trial, a different set of 64 piglets were fed a diet containing a galacto-oligosaccharide (1%) from milk whey, and two fructo-oligosaccharides (4%) from chicory inulin and sugar beet (SbFOS). There was virtually no effect on the hindgut microbiota, except for SbFOS at 4% which tended to increase the endogenous bifidobacteria. Then, in a third trial employing 128 weaning pigs, the probiotic strains Ra 18 and Su 891 were tested individually, at different doses (0; 10 7 ; 10 9 ; 10 11 per pig per day) and combined with 0% or 2% SbFOS supplementation. It was found that Ra 18 improved the live weight growth linearly, while the Su 891 did not. The FOS supplementation showed no interaction with the Ra 18 or Su 891 probiotics for growth performance and no effect on this response criterion. Our selection procedure has highlighted that B. animalis subsp. lactis Ra 18, at 10 11 CFU per pig per day, appears to be the best probiotic choice for improved growth performance in weaning piglets.