Mannan oligosaccharides (MOSs) are often referred to as one of the potential alternatives for antimicrobial growth promoters. The aim of the paper is to provide a review of mannan oligosaccharide products in relation to their growth promoting effect and mode of action based on the latest publications. We discuss the dietary impact of MOSs on (1) microbial changes, (2) morphological changes of gut tissue and digestibility of nutrients, and (3) immune response of pigs after weaning. Dietary MOSs maintain the intestinal integrity and the digestive and absorptive function of the gut in the post-weaning period. Recent results suggest that MOS enhances the disease resistance in swine by promoting antigen presentation facilitating thereby the shift from an innate to an adaptive immune response. Accordingly, dietary MOS supplementation has a potential growth promoting effect in pigs kept in a poor hygienic environment, while the positive effect of MOS is not observed in healthy pig herds with high hygienic standards that are able to maintain a high growth rate after weaning.

Summary Th e objective of the present study was to investigate the eff ect of an essential oil product on growth performance and cellular immune response of 28-day-old weaned piglets. A total of 348 piglets (50% gilts, 50% barrows) were assigned to three dietary treatments (6 pens/trt). Th e basal diet was a commercial feed that was supplemented without any growth promoter (NC), with antibiotic growth promoter of 40 ppm avilamycin (PC), or with 0.25 g of an essential oil product (EO) per kg of feed. All pigs were immunized by inactivated Aujeszky’s disease virus vaccine at week one and three of the experiment (28- and 44-days-age, respectively). Blood samples were taken four times (on day one, 16, 24, 32 of the experiment) for lymphocyte stimulation (LST) tests with ConA, PWM, PHA used as non-specifi c and Aujeszky virus used as specifi c mitogens from 2 pigs/pen. All piglets were individually weighed on day 0, 8, 16, 24 and 32 of the trial. Th ere was no signifi cant diff erence among average daily gain, feed intake and feed conversion ratio of piglets fed diff erent dietary treatments. Th e non-specifi c LST test at the 4th blood sampling showed higher values in pigs received feeds with essential oil supplementation (EO) than that of the positive (PC) and negative control (NC) groups (P<0.05). However, no signifi cant diff erence in specifi c immune response of pigs in diff erent dietary treatments was found. It can be concluded that essential oil supplementation may enhance the non-specifi c immunocompetence of 28-day-old weaning pigs without compromising their growth performance.

Several studies report that dietary mannan-oligosaccharides (MOSs) improve the growth performance of piglets, however, only a few studies focus on nutrient digestibility. The aim of the study was to investigate the effect of dietary MOS on ileal digestibility of nutrients and on N-balance and growth performance of piglets weaned at 28 days of age. Three experiments were conducted: a digestibility trial with a total of 30, simple T-cannulated piglets (Exp. 1), a N-balance trial with a total of 48 intact piglets (Exp. 2) and a performance trial with a total of 324 piglets (Exp. 3). In Exp. 1 and 2, the same five dietary treatments were carried out by supplementing the basal diet with 0, 1, 2, 4 g MOS or with 0.2 g antibiotic growth promoter (AGP, Avilamycin) per kg of diet. In Exp. 3, three dietary treatments were used as follows: the basal diet was supplemented no additive, 2 g MOS or 0.2 g AGP (Avilamycin) per kg of diet. Dietary MOS (2 or 4 g/kg) enhanced the ileal digestibility of crude protein similar to antibiotics. Addition of 1 g/kg MOS significantly increased the digestibility of Ca and P by 8.4% and 7.7% units, respectively; however, further increment did not enhance the absorption. Addition of 1 or 2 g/kg MOS significantly increased the ileal digestibility of lysine, methionine, cystine and threonine with the same magnitude or even more than the AGP. In our study, MOS supplementation had no influence on N-balance and growth parameters. Because of the better apparent ileal digestibility of certain nutrients, however, the protein, lysine, methionine, cystine, threonine, Ca and P contents of the diet can probably be reduced without weakening the rearing performance of piglets, when the diet is supplemented with 2 g/kg MOS.

The effect of different doses of mannan-oligosaccharide (MOS) on specific and non-specific immune responses was studied in piglets, weaned at 28 days. A total of 58 piglets were used in six groups. Five groups were fed 0, 1, 2, 4 g MOS product per kg diet or with growth promoting antibiotics and immunized by inactivated Aujeszky’s disease virus (AyV) vaccine at week 1 and 3 of the experiment (35 and 49 days). A sixth group, receiving the same non-supplemented diets was not immunized. Blood samples for lymphocyte stimulation (LST) and AyV neutralization (VN) tests were taken from all pigs on the first day of the experiment and at weekly intervals for 5 weeks. At week 8, the immunized piglets were infected orally with transmissible gastroenteritis virus. All piglets were weighed and slaughtered at week 10, digesta from small intestine were collected and tested for the presence of secretory (s)IgA. Feeding MOS supplementation resulted in enhanced specific and non-specific immune responses, however, a regressive dose-response of MOS was observed. Both the specific cellular (LST) and humoral responses (VN) were enhanced after 2 weeks of feeding 1 g/kg MOS and significantly differed from the antibiotic positive control. The same tendency was detected in case of the non-specific LSTs, although these started some weeks later showing significant differences by the fifth week. Higher doses of MOS had no further beneficial effect on systemic immunity. In addition, 1 g/kg MOS supplementation group also showed some advantage in local immune responsiveness. Therefore, based on the studied immune variables, 1 g/kg MOS product is suggested in the diet of weaned piglets.

Several publications have reported that products containing mannan olligosacharides (MOSs) can be potential candidates of the replacement of growth promoting antibiotics. The number of studies and reviews related to MOS research has increased in recent years; however, there are hardly any detailed reviews discussing the mode of action of MOS and the effect of MOS on the performance of pigs. The objective of this review is to present the so far known mode of action of yeast cell derivated MOS discussing the following topics: the effect of dietary MOS supplementation on the gut microflora, on the immune variables of livestocks and on the structural and functional development of the gut. A further aim of this work is to summarize the factors affecting the growth promoting effect of MOS products.Based on approximately 100 relevant publications the authors concluded the followings: due to the fact that carbohydrates with different composition (different chemical bounds) are called MoSs, the effectiveness of the products in biological response can be different. Considering that MOS products have a potential to reduce the number of pathogens in the gut, and modulate the specific and non-specific immune response of the host animal, they might be appropriate to increase the performance of livestock being kept under higher environmental pressure. In addition the gut maturation is likely enhanced by dietary MOS, thus reduces the depression in efficiency of digestion right after weaning and results in a better nutrient absorption. Mode of action of MOS products compounds these elements that might cause growth promoting effect, particularly for those animals that perform bellow their genetic capacity. Based on the relevant literature, the cell wall derivates can be beneficially used in particular in nutrition of gestating and lactating sows (0.2%), as well as of weaned piglets (0.1-0.3%).