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The objective of this study was to investigate the effects of yeast culture (YC) on the growth performance, caecal microbial community and metabolic profile of broilers. A total of 350 1‐day‐old healthy Arbor Acres broilers were randomly assigned to seven treatment groups. The first group received a basal diet without YC supplementation, whereas the remaining groups received a basal diet supplemented with either YC fermented for 12, 24, 36, 48 or 60 hr, or a commercial YC product (SZ2). MiSeq 16S rRNA high‐throughput sequencing was used to investigate the bacterial community structure, and gas chromatography–mass spectrometry was used to identify the metabolites in the caeca of broilers. The broilers that received a diet supplemented with YC had a higher average daily gain and average daily feed intake than those received YC‐free or SZ2‐enriched diets. The feed conversion ratio (FCR) of YCs fermented for 24 hr resulted in the best feed efficiency, whereas the FCR of YC fermented for 60 hr resulted in poor feed efficiency (p <.05). In the caeca of broilers, the bacterial communities were well separated, as determined by principal component analysis, and the proportions of the eight genera were significantly different among the seven groups (p <.05). The genus Akkermansia was the most abundant when the diet supplemented with YC fermented for 24 hr (p <.05). Furthermore, the Firmicutes/Bacteroidetes ratio was positively correlated with the FCR in the caecum (r =.47, p <.005). Five differentially expressed metabolites (i.e., L‐alanine, benzeneacetic acid, D‐mannose, D‐arabitol and cholesterol) were identified in the caeca of broilers that received diets supplemented with YCs fermented for 24 or 60 hr. In summary, the different fermentation times of the YCs can markedly improve the growth performance and FCR of broilers by altering the caecal microbial community, and the growth performance which is related to the changes in key metabolic pathways. [ABSTRACT FROM AUTHOR]

The effects of yeast culture (YC) supplementation and the dietary ratio of non‐structural carbohydrate to fat (NSCFR) on growth performance, carcass traits and fatty acid profile of the longissimus dorsi (LD) muscle in lambs were determined in a 2 × 3 full factorial experiment. Thirty‐six Small‐tailed Han lambs were randomly divided into six groups with six replicates per group. The lambs were fed one of the six pelleted total mixed rations (TMRs) for 60 days after 15 adaption days. The six rations were formed by two NSCFRs (11.37 and 4.57) and three YC supplementation levels (0, 0.8 and 2.3 g/kg dietary dry matter). The average daily gain (ADG), dry matter intake (DMI) and feed conversion ratio (FCR) data of each lamb were recorded and calculated. All the lambs were slaughtered for determining carcass traits and fatty acid profile of the LD muscle. DMI was significantly increased (p < 0.05) in a quadratic fashion with 0.8 g/kg of YC supplementation. Carcass weight (CW) and dressing percentage (DP) were significantly increased (p < 0.05) in a linear fashion with 2.3 g/kg of YC supplementation. Animals fed with high‐NSCFR diet had higher (p < 0.05) contents of myristoleic acid (C14:1), pentadecanoic acid (C15:0) and cis‐10‐heptadecenoic acid (C17:1), and lower (p < 0.05) stearic acid (C18:0) content in LD muscle than those fed with low‐NSCFR diet. Moreover, ADG, growth rate (GR), backfat thickness (BFT), percentages of crude fat (CF) and crude protein (CP), SFAs, MUFAs and PUFAs in LD muscle, were significantly affected (p < 0.05) by interaction of dietary NSCFR and supplemental YC level. Overall, YC not only improved the growth performance and carcass traits of the animals but also modified the fatty acid profile of the LD muscle. Furthermore, the effects of YC supplementation may depend on dietary compositions. [ABSTRACT FROM AUTHOR]

Highlights • We studied effects of diet composition and yeast culture (YC) on rumen. • Diet composition × YC interaction was recorded in VFAs, NH 3 -N and bacterial community. • YC impact mainly depended on the diet composition. Abstract This study aimed to evaluate the effects of yeast culture (YC) supplementation and the ratio of non-structural carbohydrate to fat (NSCFR) on rumen fermentation parameters (RFPs) and bacterial-community composition (BCC) using 6 ruminally cannulated sheep in a 2 × 3 factorial experiment. We formulated 6 dietary treatments with 3 levels of YC supplementation (0, 0.8 and 2.3 g/kg of dietary dry matter) and 2 dietary NSCFRs (17.02 and 5.60). Each animal was fed 1 of 6 diets in a 6 × 6 Latin square arrangement during the experiment. Ruminal liquid was sampled at 0, 2, 4, 6, 8, and 12 h after morning feeding on days 16 and 17 (last 2 days) in all 6 of the Latin square periods. The concentrations of acetic acid, butyric acid and total volatile fatty acid (TVFA) were significantly (p < 0.05) increased and the pH values were significantly (p < 0.05) decreased when the animals fed on high-NSCFR diet (H diet) with 2.3 g/kg of YC at 2 h after feeding compared with that on the low-NSCFR diet (L diet). However, the concentrations of ammonia nitrogen (NH 3 -N) were higher (p < 0.05) in all H groups than that in L groups. The relative abundances of Prevotella_1 were higher in all L groups (p < 0.05), while Lachnospiraceae_NK3A20 and Olsenella were higher in H groups (p < 0.05). Compared with L groups, the relative abundances of Candidatus_Saccharimonas and [Ruminococcus]_gauvreauii of H groups were increased when supplemented with YC (2.3 g/kg; p < 0.05). A significant increased relative abundance of Butyrivibrio_2 was observed in the L group (2.3 g/kg YC). Overall, the RFPs and BCC were influenced by both dietary NSCFR and YC supplementation. There was significant interaction between dietary NSCFR and YC supplementation in the aspects of VFAs, NH 3 -N and all genera of BCC. [ABSTRACT FROM AUTHOR]