The impact of probiotic live yeast in a barley grain-based diet on rumen microbial communities, fermentation, and histology of artificially reared lambs

This study aimed to investigate the effect of dietary supplementation with a probiotic live yeast Saccharomyces cerevisiae on rumen microbial communities, enzymatic activities, volatile fatty acid concentrations, and histology in artificially reared lambs fed a diet rich in fermentable carbohydrates. After colostrum administration, forty-two Chios lambs were divided into two homogenous groups (n = 21); the control (C) and probiotic supplemented group (P) and were artificially reared until the 45th day (d) of age. From the 30th until the 106th d of lambs’ age, both groups were fed alfalfa hay and barley grain-based concentrate mix ad libitum. Moreover, 100 g of concentrate including 0.1 g of Saccharomyces cerevisiae CNCM I-1077 live yeast (10¹⁰ CFU/g) was offered to P lambs to ensure a constant intake of the yeast. Although no difference was evident for the alpha-diversity, several interesting features were found for beta-diversity. Butyrivibrio, Pseudobutyrivibrio, and acetate producer Sphaerochaeta were significantly more abundant (P = 0.029, P = 0.029 and P = 0.008, respectively) in P- compared to C-fed lambs at 100 d, while population of lactate users were varying significantly in P- and C- fed lambs at 100 d [higher abundance of Megasphaera in C- (P = 0.001) and Anaerovibrio in P-fed lambs (P = 0.046), respectively]. Acidaminococcaceae and Clostridia UCG-014 were found in a lower abundance (P = 0.059 and P = 0.008, respectively) in P- compared to C-fed lambs at 100 d. Both ruminal pH and the activities of fibrolytic enzymes did not differ amongst the dietary treatments, while total volatile fatty acid concentrations were increased (P < 0.001) in P- compared to C-fed lambs at 100 d. As regards the serosa, the muscular layers, the intramural vasculature and innervation, our results showed no effect in rumen histology due to the dietary treatment, however, changes were evident in the mucosa where all constituent layers of the epithelium presented distinctly and with similar thickness, especially around papillae, the collagen and reticular fibers were more densely and evenly packed, and prekeratins and keratins delineated more distinctly epithelial pegs in P-fed when compared to C-fed lambs. The inclusion of live yeast S. cerevisiae CNCM I-1077 promoted rumen microbiota stability and limited extensive keratinization of the epithelium due to a highly fermentable carbohydrate diet formulation.