Effects of buffer and Megasphaera elsdenii as pH regulators, on histomorphometry and histopathology of small and large intestine of Arabian fattening lambs fed with high concentrate diets

In the small intestine, villi height, crypt depth, epithelial tissue thickness, and the ratio of villi height to crypt depth play a significant role in the final stages of digestion and absorption of nutrients from the gastrointestinal tract (Strusińska et al., 2009, Wang et al 2009). The special shape of the villi and the presence of small intestinal micropores increase the level of intestinal absorption and have a direct effect on their efficiency and function (Kreikemeier et al 1991). The presence and absorption of volatile fatty acids are the keys to developing the tissue structure of the gastrointestinal tract (Attaix and Meslin 1991 and Vi et al 2004). The effect of volatile fatty acids on stimulating cell proliferation and growth of gastrointestinal tissue is not limited to the reticulum and rumen, but also affects the small intestinal villi. (Wang et al 2009). Feeding animals with high concentration diets could cause metabolic problems including acidosis (Aschenbach et al 2002). Its results are included the death of gram-negative bacteria and the release of endotoxins (lipopolysaccharides) into the bloodstream from the damaged rumen wall, activating inflammatory mediators, and affecting the productive function of animals (Garcia Diaz et al 2018). The possible effects of microbial additives on the gastrointestinal tract are through the regulation of ruminal pH and the immune system, which are useful for improving digestion, function, and animal health (Ding et al 2008 and Silberberg et al 2013). The use of yeast and other biologically active compounds such as lactic acid consuming bacteria compared to chemical buffers could be effective in reducing inflammation caused by acidosis. (Aschenbachet al 2019)

Twenty-four Arabic male lambs with Four months old and initial body weight of 23.9±3.15 kg were used in a completely randomized design with three treatments and eight replicates. The trial period consisted of 77 days (11 weeks) including 14 days of habituation period and 63 days (9 weeks) of the recording period. The lambs were randomly assigned to one of three treatments: 1-control (no additive) 2-control + Sodium bicarbonate (1% daily diet in two meals) 3-control + Megasphaera elsdenii and Saccharomyces cerevisiae (bacterium - yeast). The amount of Megasphaera elsdenii was 3 ml per animal (4.5 × 108 cfu / ml) plus 2 g of Saccharomyces cerevisiae (DFM) fed to the animals daily in the morning (Sedighi and Alipour 2019). The diets were adjusted using the Small Ruminants Nutrition Requirements (NRC 2007). The lambs were fed a fully mixed (TMR) ratio of 30% forage and 70% concentrate at two meals (8 and 16 hours) with free access to water. For the histological trial of the intestines, fragments were separated from the middle part of the three regions of the duodenum, jejunum, and ileum, and the middle part of the large intestine and each part were emptied with formalin rinsing, Then the two ends of each piece were closed and neutral formalin 10 % was injected into them, and separately in containers with lid containing formalin 10 % were placed. Micrometric studies of different parts of the small intestine: Villus height, crypt depth, villus width, and thickness of tunica muscularis were examined histomorphometrically.

villi height, crypt depth, and villi surface of the duodenum in bacterium - yeast treatment were higher than other treatments (P<0.05). The thickness of tunica muscularis in the buffer treatment was higher than other treatments (P<0.05). The width of duodenum villi in the buffer and bacterium-yeast treatments was higher than the control treatment and was significant in the bacterium - yeast treatment than the control treatment (P<0.05). No significant difference was observed between jejunum tissue indexes in the treatments. The height of ileum villi in buffer and bacterium - yeast treatments was higher than the control treatment and was significant in the bacterium - yeast treatment than the control treatment (P<0.05). Crypt depth and villi surface of ileum in bacterium - yeast treatment was higher than other treatments (P<0.05). In buffer and bacterium - yeast treatment due to pH adjustment and increased activity of fiber degrading bacteria which produce more acetate (Lechartier and Peyraud 2011 and Malekkhahi et al 2016) The dimensions of the villi of the small intestine increased. In Histopathological investigation of the duodenum in all three treatments of control, buffer, and bacterium -yeast, infiltration of mononuclear inflammatory cells in the parenchymal mucosa was observed. In terms of lesion severity, the highest involvement was in the mucosa of the control treatment and then in the sodium bicarbonate buffer treatment and was less in the bacterium-yeast treatment than the other two treatments. In the bacterium-yeast treatment, the penetration of mononuclear inflammatory cells in the parenchyma of jejunal mucosa was much less than control and buffer treatments. In bacterium -yeast treatment, the frequency of Peyer's patches in the ileum is reduced compared to other treatments, which indicates a reduction in tissue inflammation. Histopathological investigation of the large intestine showed the infiltration of mononuclear inflammatory cells in the control treatment. The penetration of mononuclear inflammatory cells in this part was less than that of the small intestine. The severity of tissue lesions in the buffer and bacterium-yeast treatments was lower than the control treatment. In bacterium-yeast treatment, the penetration of mononuclear inflammatory cells was greatly reduced.

Compared to the control, the use of pH regulators in terms of histopathology reduce tissue damage in the small intestine and large intestine. The use of pH regulators, especially the bacterium-yeast composition, has led to the development of intestinal mucosal indices such as villi height and crypt depth. In addition, the destructive effect of acidosis, such as the penetration of inflammatory cells and necrosis, which was the result of increased consumption of high concentrates on digestive tissues; Has been reduced. Therefore, the use of pH regulators, especially bacterium - yeast, improve the tissue structure of the small intestine and they are reduced tissue damage in the small and large intestines.