Yeasts in diets for piglets

Weaning as currently practiced represents one of the most critical periods in the raising of pigs. It is characterized by a diminution in feed consumption, leading to a state of severe anorexia, an increased sensitivity to digestive problems or microbial infections, and a slow down of growth. The change in the nutrient substrate also brings with it major modifications in intestinal function, influencing nutrient utilization, metabolism or even protein synthesis. In addition, the digestive microflora, whose major function would seem to be to protect the digestive tract against invasion by enteropathogenic bacteria, undergoes major changes during weaning. In the past these risks were reduced by the systematic application of sub-therapeutic doses of growth-promoting antibiotics in the feed. However, the risk of development of bacterial strains resistant to antibiotics led the EU to prohibit their use. Since then, the animal feed industries have been searching for alternatives capable of maintaining production levels and the health of the animals. The Saccharomyces cerevisiae Sc 47 yeasts (Actisaf®), their cell wall fractions or extracted fractions (mannan oligosaccharides, β-glucans) would seem to be possible alternatives.

On the other hand, diets for pigs tend to contain more fibre due to the availability of cereal fibre-rich by-products and dietary utilisation of live yeasts became usual due to their influence on digestive microflora. However, information available on the use of yeasts on high-fibre diets is lacking.

The aim of the present study is therefore to evaluate the efficacy and to study the mechanisms involved in the use of the S. cerevisiae Sc 47 yeasts (Actisaf) in diets for piglets.

Initially, two trials were carried out to evaluate the effect of including Actisaf in diets for weanling piglets and evaluate its effects on growth performance, nutrient utilisation and some morphological and immunological parameters. In experiment 1, 90 weaning piglets were distributed among 3 groups corresponding to the control diet and 2 diets supplemented with 0.5 or 1 g/kg of Actisaf. The experiment lasted 5 weeks and, at the end, 16 piglets of treatments control and the high dose of Actisaf were slaughtered for intestinal sampling. Overall, increases in weight gain and in final bodyweight were observed (P<0.05) and, feed:gain ratio tended (P=0.12) to improve with yeast diets. Villous height was not affected (P>0.10) by yeast diets, but they reduced (P=0.07) the number of intra-epithelial lymphocytes and increased volatile fatty acid production and percentage of acetate. In experiment 2, 24 piglets were used to evaluate nutrient utilisation and N retention. Dry matter, energy and protein digestibility was similar among treatments (P>0.10). However, neutral detergent fibre and hemicelluloses digestibility (P<0.001) and nitrogen retention increased with yeast diets (P<0.001), in agreement with the increased weight gain observed in both experiments.

In a second set of trials, two other experiments were conducted to evaluate the association between dietary fibre level and Actisaf on piglet growth performance and nutrient utilisation. In trial 3, 144 weaning piglets were distributed among 4 groups corresponding to low and high fibre diets supplemented or not with 5*109 UFC / kg of live yeasts. No statistical effects were observed during the 1st two weeks after weaning. However, during the subsequent 3 weeks, piglets fed low fibre levels as well as those fed yeasts diets consumed more feed (P<0.05) and exhibited a high daily weight gain (P=0.08). A beneficial association of yeast and fibre-rich diets was also observed for daily weight gain (P<0.05) and piglet liveweight (P=0.08). In trial 4, thirty-six 15-kg piglets were used for digestibility measurements. Nitrogen (P=0.08), NDF and ADF digestibility (P<0.05) increased with dietary fibre whereas that of dry matter, nitrogen (P<0.05), energy (P=0.10), NDF and ADF (P<0.01) increases with live yeasts.

From results of this study, it can be concluded that utilization of Actisaf has positive effects on productive performance after weaning and its inclusion on piglet diets could be recommended, in particular on high fibre diets.