Yeasts are single-cell eukaryotic microorganisms that are largely employed in animal nutrition for their beneficial effects, which are owed to their cellular components and bioactive compounds, among which are mannans, β-glucans, nucleotides, mannan oligosaccharides, and others. While the employment of live yeast cells as probiotics in poultry nutrition has already been largely reviewed, less information is available on yeast-derived products, such as hydrolyzed yeast (HY) and yeast culture (YC). The aim of this review is to provide the reader with an overview of the available body of literature on HY and YC and their effects on poultry. A brief description of the main components of the yeast cell that is considered to be responsible for the beneficial effects on animals’ health is also provided. HY and YC appear to have beneficial effects on the poultry growth and production performance, as well as on the immune response and gut health. Most of the beneficial effects of HY and YC have been attributed to their ability to modulate the gut microbiota, stimulating the growth of beneficial bacteria and reducing pathogen colonization. However, there are still many areas to be investigated to better understand and disentangle the effects and mechanisms of action of HY and YC.

The current study was performed to explore the effects of dietary supplementation of Saccharomyces cerevisiae hydrolysate (SCH) on growth performance, immune function, and intestinal health in broiler chicken. A total of 300 Ross 308 male broilers (1-day-old) were randomly assigned to 2 dietary treatments including a basal diet (control group), and a basal diet supplemented with SCH feed additive (500 mg/kg in starter and grower phase, and 250 mg/kg in finisher phase). Each treatment had 6 replicates with 25 birds each. The results showed that the addition of SCH promoted growth during d 15 to 28 (P < 0.05). Although the addition of SCH had no significant effect on the intestinal relative indexes, it significantly increased the jejunum villus height (VH) and the ratio of villus height to crypt depth (VCR) of jejunum, and decreased the crypt depth (CD) of ileum (P < 0.05). Furthermore, SCH addition significantly downregulated the mRNA expression of immunomodulatory genes (TNF-α, IL-1β, and IL-6), and upregulated the tight junction genes (ZO-1 and Claudin-1) (P < 0.05). High throughput sequencing analysis of bacterial 16S rRNA revealed that dietary SCH supplementation altered cecum microbiota. Alpha diversity analysis showed that a higher bacterial richness in cecum of broilers fed with SCH. The composition of cecum microbiota regulated by SCH addition was characterized by an increased abundance of Firmicutes and a reduced abundance of Bacteroidetes. At the genus level, dietary SCH resulted in a decrease of Bacteroides and an increase of short-chain fatty acids (SCFA) -producing bacteria including Lactobacillus and Faecalibacterium. Taken together, dietary SCH supplementation can stimulate the growth of broilers by regulating the intestinal immunity and barrier function, and improving the intestinal morphology, which may be related to the enhancement of bacterial diversity and the changes of intestinal microbial composition.

The aim of this study was to test the hypothesis of an improved gut environment of post-weaning piglets when administered a blend of essential oils (EO; thymol and cinnamaldehyde) and an enzyme combination (xylanase and β-glucanase (XB)) either alone or in combination. To assess the effect of dietary treatments, faecal nutrient digestibility and microbial counts, as well as ileum histology and gene expression of inflammatory mediators were evaluated. One hundred and ninety-two weaned piglets were allocated into four experimental treatments, and fed the basal diet (CTRL) either without or with EO, XB or their combination (EO+XB) for a 42-day period. The experiment concerning digestibility was designed with two periods (period I: days 15 to 21; period II: days 29 to 35) and the faeces were collected on days 20, 21, 34 and 35. On day 42, six piglets from each treatment were slaughtered. It was found that EO, XB and EO+XB supplementation did not affect (P>0.05) the growth performance of the piglets from days 0 to 42. Moreover, no dietary effect on faecal score was observed. Faecal digestibility of dry matter, organic matter, ash, dietary fibre, lipid, CP and NDF were increased from period I to period II (P<0.01 to P=0.06), while no effect (P>0.05) of EO, XB or their combination on the faecal digestibility was observed at both periods. Compared with the CTRL diet, dietary XB reduced the faecal Lactobacillus and Escherichia coli counts but increased the Lactobacillus to Coliforms ratio on day 42 (P=0.02, 0.03 and 0.03, respectively), and all the additives supplementations decreased the counts of faecal Coliforms on day 42 (P<0.01). XB supplementation increased the villus to crypt ratio (P=0.04) and reduced the mucosal macrophages number (P<0.01) in the ileum compared with the CTRL group, and dietary EO or EO+XB decreased the number of lymphatic follicles (P=0.01 and P<0.01, respectively) and mucosal macrophages (P=0.02 and P<0.01, respectively). In addition, the interleukin (IL)-1α was downregulated in piglets treated with EO+XB compared with the EO group (P=0.02). In conclusion, the administration of EO, XB or their combination was effective in improving ileum histology, and EO+XB supplementation might benefit the modulation of the expression of ileum inflammatory cytokines in piglets.

The aim of this study was to evaluate the effects of mannan oligosaccharides (MOS) on gut health and performance in post-weaning piglets. In total, 40 piglets were divided into two experimental groups and fed a basal diet with (TRT) or without (CON) 0.2% mannan oligosaccharides for 35 days. Growth performance was determined weekly and faecal microbial composition on days 0, 14 and 35. On day 36, histometrical evaluations were performed on duodenal, jejunal, ileal, and colon samples. mRNA gene expression of inflammation-related genes was evaluated in samples of ileal Peyer’s patches (IPP). MOS administration improved feed efficiency in the last two weeks of the trial (p < 0.05), and a decreased clostridia content was found in faeces at day 14 (p = 0.05). TRT piglets showed increased duodenal villi height (p < 0.05), and reduced mRNA levels of Tumour Necrosis Factor α (p < 0.05) and Toll-Like Receptor 4 (p < 0.01) in IPP. Our results suggest beneficial effects of MOS supplementation on gut morphology and the expression of inflammation-related genes in post-weaning piglets, accompanied by increased feed efficiency.

The aim of this study was to evaluate the bioavailability of ingested selenium (Se) yeast in laying hens and its effects on performance, eggshell quality, and tissue Se distribution. Forty-eight ISA brown laying hens were divided into 3 treatment groups: Group C, fed a basal diet containing 0.11 mg Se/kg of feed; Group SS, fed a basal diet plus 0.4 mg/kg of feed of Se from sodium selenite; and Group SY, fed a basal diet plus 0.4 mg/kg of feed of Se from selenium yeast. Feed intake, egg mass ratio, and production performance were not affected by Se supplementation, regardless of the Se source. Egg weight (+3.61% and +2.95%), eggshell weight (+4.26% and +5.38%), and eggshell surface (+2.43% and +1.96%) were higher (P<0.05) in SS and SY than C, whereas breaking strength was increased in SY (P<0.01). Breast muscle, liver and skin Se levels were higher in SY than in C, while kidney Se content was higher in SS hens. Eggs from SY had higher Se levels than SS. Blood metabolites were not affected in SS or SY groups than C. A higher Se level was detected in eggs and breast muscle of SY hens (P<0.05). Selenium-enriched eggs and edible tissues from organic Se sources in poultry diet could improve antioxidant status in humans and reduce possible Se deficiency-related diseases.