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According to different studies, yeast cell walls can positively influence the performance parameters, the intestinal microbiota and immune reaction of animals. However, the results of the different studies are inconstant. Differences seem to be dependent on origin of the yeast sources, production processes and amounts of β-glucans and MOS in the different yeast cell wall preparations.
This study was conducted to investigate whether a yeast cell wall product can carry out dose-dependent effects on animal performance, the composition and activity of the intestinal microbiota, the immune system and the nutrient digestibility in broiler chickens. For that purpose one day-old male broiler chickens (Cobb Germany Avimex GmbH) were divided into two consecutive trial runs and samples were taken during as well as at the end of the 35-day-lasting fattening period for immunological, microbiological and digestibility analysis. All animals received as diet a starter (d 1 - 14) and grower mixture (d 15 - 35) based on soybean meal, maize and wheat. Four experimental groups were fed the product Immunowall® in rising concentrations (0.05 %, 0.10 %, 0.20 % and 0.30 %) over the whole fattening period, while the fifth experimental group served as control. Seventeen broiler chickens per floor pen each representing a single experimental unit. The animals received water and feed ad libitum.
The performance parameters were recorded weekly. On day 21 the animals were orally vaccinated against NDV and blood samples were taken directly before as well as seven and 13 days after the vaccination for the quantification of the antibody titer against NDV, the determination of the phagocytic acitivity of the monocytes and complete blood counts. At the end of each trial run one broiler chicken from each experimental unit was slaughtered. To quantificate the lactobacilli, bifidobacteria, enterobacteria and Escherichia/Hafnia/Shigella spp. digesta samples were taken from the crop, ileum and caeca. These samples were also used for the measurement of the pH-value and the determination of the bacterial metabolites. Digesta from the duodenum were collected to measure the intestinal IgA concentration. Thymus, spleen and bursa fabricii were removed and weighed to determine the relative organ weights. In order to examine the effect of the yeast cell wall product on the nutrient digestibility, five animals of each experimental unit were randomly selected, slaughtered and samples of the ileum were collected to determine the dry matter content and the apparent ileal digestibility of protein, fat and starch on day 36. All collected data were analyzed by using a one-factorial analysis of variance or a Kruskal-wallis-test as well as a polynomial contrast analysis.
The yeast cell wall product had an impact on the performance parameters. Chicken fed the yeast cell wall product showed dose-dependent effects on the body weight in the second and third week of age (p = 0.029 and p = 0.089). This was reflected in a better feed conversion ratio in the third week of age (p = 0.083). In the last two weeks of the fattening period the chickens of the control and the experimental group, which were fed 0.05 % of the yeast cell wall product showed a higher body weight gain in the analysis of variance and contrast analysis and tended to have a better feed conversion ratio in the linear contrast analysis in the last week. The feed intake in the first seven days of age was higher (p = 0.002) and the feed conversion ratio tended to be lower (p = 0.081) in the experimental group, which received 0.30 % of the yeast cell wall product. Over the whole fattening period there were no differences regarding the performance parameters between the five experimental groups. Concerning the quantification of the different bacteria species, only the concentration of the lactobacilli was different between the experimental groups (p = 0.027). A positive dose-dependent effect was detected for the lactobacilli in the digesta of the crop and ileum in the experimental groups with the yeast cell wall supplementation. Similar trends were observed regarding the lactate and acetic acid concentration in the digesta of the crop and ileum. Inverse dose-dependent effects were noticed in the pH-value of the crop digesta. The ammonia concentration in the crop, ileum and caeca were not affected by the addition of the yeast cell wall product. The concentration of propionic acid was reduced in the experimental group, which received 0.30 % of the yeast cell wall product in contrast to the groups with the addition of 0.05 % and 0.10 % of the yeast cell wall product (p = 0.047). The relative immune organ weights, the intestinal IgA concentration, the phagocytic acitivity of the monocytes, the antibody titer against NDV as well as the concentrations of the monocytes and heterophils in the blood of the broiler chickens were not affected by the addition of the yeast cell wall product, whereas the concentrations of the lymphoyctes in the blood were numerically higher at all three collection time points. Furthermore, the lymphocytes and the T- and B-lymphocytes were partly tendentially and significantly higher on day 28 and 34 in the experimental groups with the addition of the yeast cell wall product. Neither the dry matter content of the ileum digesta nor the apparent ileal digestibility of fat and starch were affected by the yeast cell wall product. In contrast, the apparent ileal digestibility of protein tended to be higher in the supplemented groups.
To conclude, the results illustrate that the addition of the yeast cell wall product had a dose-dependent impact on the performance parameters, the composition and acitivity of the intestinal microbiota, the adaptive immune system and the apparent ileal digestibility of protein in healthy broiler chickens. The results indicate that the yeast cell wall product could be used to improve the immune response, the composition and activity of the intestinal microbiota and the performance parameters in the first three weeks of age of the chickens. It should be clarified, how far the addition of the yeast cell wall product can be used in broiler chickens under less favourable housing conditions in order to improve the health and performance of the animals.