Live yeast and inactivated yeast products are considered to have a high potential to improve piglet’s performance due to its ability to positively modulate the intestinal microbiota and favor animal health (Shen et al., 2009; Stuyven et al., 2009; Trckova et al., 2014; Broadway et al., 2015). In this study, there was no significant effect of AY levels on growth performance of these animals, corroborating with Molist et al. (2014) and Jiang et al. (2015). The lack of effect of AY supplementation on piglet performance in the current study may have occured because according to some researchers the effect of yeast supplementation is more pronounced in animals subjected to sanitary challenges (Finck et al., 2014; Neumann et al., 2020), which was not the case in the current study. Additionally, although there were no significant differences between treatments, it was observed that the AY supply promoted a considerable numerical increase in the gain:feed of the nursery piglets. Therefore, it is suggested that further studies be performed to analyze the possible effects of supplementing higher levels of AY in piglets’ diet at nursery phase. Regarding weight category, heavy piglets had higher ADFI than light piglets in all evaluated periods, corroborating with Zotti et al. (2017) and Faccin et al. (2019).
AY supplementation for nursery piglets linearly decreased the blood concentrations of monocytes. These immune system cells are responsible for defense against infectious microorganisms and there is often an increase in its blood concentrations in cases of subclinical and clinical infections (Ganner and Schatzmayr, 2012; Seo et al., 2015). AY components, such as β-glucans, have immunomodulatory activity (Williams et al., 1996). Therefore, it can be suggested that the dietary supply of AY reduced the infectious challenge imposed on nursery piglets.
After weaning, the villus height tend to decrease and the crypt depth tend to increase, which results in a lower digestive and absorptive capacity of piglets, negatively affecting their growth performance (Bauer et al., 2006; Czarneck-Maulden, 2008). In this study, the dietary supplementation of AY for nursery piglets linearly increased the values of villus height, mucosal thickness and absorptive area of the duodenum, as well as the mucosal thickness and villus height:crypt depth radio of the jejunum. These results indicated that the dietary supplementation of AY could help enhance the small intestine development and physical intestinal epithelial barrier of early-weaned piglets. However, this improvement in intestinal morphometry of piglets fed diets containing AY was not enough to enhance the digestive and absorptive capacity and, consequently, the ADG and and gain:feed of these animals.
The intestinal epithelium tissue is continually being renewed, due to aging, the exhaustion of its cells or action of chemical agents associated to the digestive processes (Cheng and Leblond, 1974; Uni et al., 1996). This intestinal epithelial renewal occurs due to the undifferentiated cells of the crypts, which undergo mitosis, originating the cellular types of the intestinal epithelium (Nasciutti et al., 2016). In this study, the dietary supply of AY for nursery piglets linearly increased the number of mitotic cells in duodenum and jejunum, which can be an indicative of fast-turnover cells. Jiang et al. (2015) reported that yeast supplementation for piglets increased the proliferation rate of intestinal epithelial cells and attributed this result to the possible effect of yeast on the release of polyamines in intestinal lumen.
Microbiota in the digestive system of piglets contributes to the defense mechanisms of the animal in differ different ways, such as prevent colonization of pathogenic bacteria. Previous studies have demonstrated that supplementation with live yeast reduced total coliforms and E. coli counts along the gastrointestinal tract of pigs, which could improve disease resistance of these animals (Jiang et al., 2015; Li et al. 2015; White et al., 2002). However, in the current study, there was no effect of dietary inclusion of AY on microbiological parameters.
The dietary inclusion of autolyzed yeast positively influences health status, intestinal morphometry and immunohistochemistry of nursery piglets. Heavy weaned piglets have better performance and intestinal morfometry than light animals.