The Duration of Increased Grain Feeding Affects the Microbiota throughout the Digestive Tract of Yearling Holstein Steers

Administration of probiotic lactic acid bacteria to modulate fecal microbiome in feedlot cattle

Modulation of animal gut microbiota is a prominent function of probiotics to improve the health and performance of livestock. In this study, a large-scale survey to evaluate the effect of lactic acid bacteria probiotics on shaping the fecal bacterial community structure of feedlot cattle during three experimental periods of the fattening cycle (163 days) was performed. A commercial feedlot located in northwestern Argentina was enrolled with cattle fed mixed rations (forage and increasing grain diet) and a convenience-experimental design was conducted. A pen (n = 21 animals) was assigned to each experimental group that received probiotics during three different periods. Groups of n = 7 animals were sampled at 40, 104 and 163 days and these samples were then pooled to one, thus giving a total of 34 samples that were subjected to high-throughput sequencing. The microbial diversity of fecal samples was significantly affected (p < 0.05) by the administration period compared with probiotic group supplementation. Even though, the three experimental periods of probiotic administration induced changes in the relative abundance of the most representative bacterial communities, the fecal microbiome of samples was dominated by the Firmicutes (72–98%) and Actinobacteria (0.8–27%) phyla, while a lower abundance of Bacteroidetes (0.08–4.2%) was present. Probiotics were able to modulate the fecal microbiota with a convergence of Clostridiaceae, Lachnospiraceae, Ruminococcaceae and Bifidobacteriaceae associated with health and growth benefits as core microbiome members. Metabolic functional prediction comparing three experimental administration periods (40, 104 and 163 days) showed an enrichment of metabolic pathways related to complex plant-derived polysaccharide digestion as well as amino acids and derivatives during the first 40 days of probiotic supplementation. Genomic-based knowledge on the benefits of autochthonous probiotics on cattle gastrointestinal tract (GIT) microbiota composition and functions will contribute to their selection as antibiotic alternatives for commercial feedlot.

Invited review: Effect of subacute ruminal acidosis on gut health of dairy cows

Subacute ruminal acidosis (SARA) is assumed to be a common disease in high-yielding dairy cows. Despite this, the epidemiological evidence is limited by the lack of survey data. The prevalence of SARA has mainly been determined by measuring the pH of ruminal fluid collected using rumenocentesis. This may not be sufficiently accurate, because the symptoms of SARA are not solely due to ruminal pH depression, and ruminal pH varies among sites in the rumen, throughout a 24-h period, and among days. The impact of SARA has mainly been studied by conducting SARA challenges in cows, sheep, and goats based on a combination of feed restriction and high-grain feeding. The methodologies of these challenges vary considerably among studies. Variations include differences in the duration and amount of grain feeding, type of grain, amount and duration of feed restriction, number of experimental cows, and sensitivity of cows to SARA challenges. Grain-based SARA challenges affect gut health. These effects include depressing the pH in, and increasing the toxin content of, digesta. They also include altering the taxonomic composition of microbiota, reducing the functionality of the epithelia throughout the gastrointestinal tract (GIT), and a moderate inflammatory response. The effects on the epithelia include a reduction in its barrier function. Effects on microbiota include reductions in their richness and diversity, which may reduce their functionality and reflect dysbiosis. Changes in the taxonomic composition of gut microbiota throughout the GIT are evident at the phylum level, but less evident and more variable at the genus level. Effects at the phylum level include an increase in the Firmicutes to Bacteroidetes ratio. More studies on the effects of a SARA challenge on the functionality of gut microbiota are needed. The inflammatory response resulting from grain-based SARA challenges is innate and moderate and mainly consists of an acute phase response. This response is likely a combination of systemic inflammation and inflammation of the epithelia of the GIT. The systemic inflammation is assumed to be caused by translocation of immunogenic compounds, including bacterial endotoxins and bioamines, through the epithelia into the interior circulation. This translocation is increased by the increase in concentrations of toxins in digesta and a reduction of the barrier function of epithelia. Severe SARA can cause rumenitis, but moderate SARA may activate an immune response in the epithelia of the GIT. Cows grazing highly fermentable pastures with high sugar contents can also have a low ruminal pH indicative of SARA. This is not accompanied by an inflammatory response but may affect milk production and gut microbiota. Grain-based SARA affects several aspects of gut health, but SARA resulting from grazing high-digestible pastures and insufficient coarse fiber less so. We need to determine which method for inducing SARA is the most representative of on-farm conditions.

Differential Responses of Digesta- and Mucosa-Associated Jejunal Microbiota of Hu Sheep to Pelleted and Non-Pelleted High-Grain Diets

In the present study, we utilized 16S rRNA sequencing to uncover the impacts of non-pelleted (HG) or high-grain pelleted (HP) diets on the microbial structure and potential functions of digesta- and mucosa-associated microbiota in the jejunum of Hu sheep. Here, we randomly assigned 15 healthy male Hu sheep into three groups and fed the control diets (CON), HG, and HP diets, respectively. The experiment period was 60 days. The HP diets had the same nutritional ingredients as the HG diets but in pelleted form. At the finish of the experiment, the jejunal digesta and mucosa were gathered for microbial sequencing. The results of PCoA and PERMANOVA showed that different dietary treatments had significant impact (p < 0.05) on digesta- and mucosa-associated microbiota in the jejunum of Hu sheep. For specific differences, HG diets significantly increased (p < 0.05) the abundance of some acid-producing bacteria in both jejunal digesta (Bifidobacterium, OTU151, and OTU16) and mucosa (Rikenellaceae RC9 gut group, and Bifidobacterium) of Hu sheep compared with the CON diets. Besides the similar effects of the HG diets (increased the acid-producing bacteria such as Olsenella, Pseudoramibacter, and Shuttleworthia), our results also showed that the HP diets significantly decreased (p < 0.05) the abundance of some pro-inflammatory bacteria in the jejunal digesta (Mogibacterium, and Marvinbryantia) and mucosa (Chitinophaga, and Candidatus Saccharimonas) of Hu sheep compared with the HG diets. Collectively, these findings contributed to enriching the knowledge about the effects of HG diets on the structure and function of intestinal microbiota in ruminants.

A Grain-Based SARA Challenge Affects the Composition of Epimural and Mucosa-Associated Bacterial Communities throughout the Digestive Tract of Dairy Cows

The effects of a subacute ruminal acidosis (SARA) challenge on the composition of epimural and mucosa-associated bacterial communities throughout the digestive tract were determined in eight non-lactating Holstein cows. Treatments included feeding a control diet containing 19.6% dry matter (DM) starch and a SARA-challenge diet containing 33.3% DM starch for two days after a 4-day grain step-up. Subsequently, epithelial samples from the rumen and mucosa samples from the duodenum, proximal, middle and distal jejunum, ileum, cecum and colon were collected. Extracted DNA from these samples were analyzed using MiSeq Illumina sequencing of the V4 region of the 16S rRNA gene. Distinct clustering patterns for each diet existed for all sites. The SARA challenge decreased microbial diversity at all sites, with the exception of the middle jejunum. The SARA challenge also affected the relative abundances of several major phyla and genera at all sites but the magnitude of these effects differed among sites. In the rumen and colon, the largest effects were an increase in the relative abundance of Firmicutes and a reduction of Bacteroidetes. In the small intestine, the largest effect was an increase in the relative abundance of Actinobacteria. The grain-based SARA challenge conducted in this study did not only affect the composition and cause dysbiosis of epimural microbiota in the rumen, it also affected the mucosa-associated microbiota in the intestines. To assess the extent of this dysbiosis, its effects on the functionality of these microbiota must be determined in future.