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Liver abscess (LA) prevalence has increased 15% for beef cattle and 25% for Holstein cattle. The prevalence of liver abscesses in the Central Plains region (CR) is greater than the Southwest region (SR) of the United States. The objective was to evaluate soil organic matter (SOM) microbiome of feedlot pens, associated LA microbiomes, and the impact of breed, location, and tylosin. Eighty-three commercial feedlot pens were sampled for SOM prior to harvesting and LA samples were collected from two commercial packing plants in Tolleson, AZ (SR) and Greely, CO (CR). Liver abscess samples were linked to SOM samples. Amplification and sequencing of the V4 variable region of the 16S rRNA gene was performed using the Illumina MiSeq. Bacterial phyla, genera, and diversity indices were reported for LA and SOM samples. Reported data is from a subset of five pens. The most prevalent genera identified in liver abscesses were Fusobacterium (64.2%) and Bacteroides (18.6%). Predominant SOM genera were Atopostipes (13%) and Clostridium (10%). Phylum SOM Shannon Weiner Index (SWI) was lower for the CR compared to the SR (0.034 vs. 0.174; P < 0.05), indicating a dominant bacterium in the CR. Atopostipes and Clostridium comprised 48% of the CR SOM, explaining the lower SWI. The SWI of SOM and liver abscesses of Holsteins are lower (P < 0.05) compared to beef counterparts. Additionally, Clostridium, Fusobacterium, and Atopostipes populations were greater (P < 0.05) in SOM of Holstein pens than beef pens. Genus richness was lower (P < 0.05) for both SOM and liver abscesses from pens of cattle fed tylosin vs. no tylosin. There is a negative correlation between SOM SWI and LA% (R2 = -0.49; P = 0.03) and LA severity (A+) (R2 = -0.44; P = 0.05). In conclusion, SOM may serve as a potential vector for liver abscesses.

Simple Summary It is well established that the functions of the gastrointestinal tract go beyond the digestion and absorption of nutrients. For instance, its constant contact with the gastrointestinal microbes and components of the diet makes it a major player within the immune system. Preserving the gut’s barrier function is essential to maintaining overall health and subsequently performance in farm animals. In cattle, multiple factors throughout their productive cycle can have negative consequences on gut health, including dietary changes. Most research in this topic has focused on rumen health, due to its critical role in digestion in bovines. However, it is increasingly evident that other sections of the gastrointestinal tract, such as the large intestine (also referred to as the hindgut), are similarly impacted by the same factors. Nutritional strategies aimed to promote rumen health have proven beneficial for overall health and performance in bovines. Targeting the hindgut might represent a window of opportunity for further improvement. Abstract An adequate gastrointestinal barrier function is essential to preserve animal health and well-being. Suboptimal gut health results in the translocation of contents from the gastrointestinal lumen across the epithelium, inducing local and systemic inflammatory responses. Inflammation is characterized by high energetic and nutrient requirements, which diverts resources away from production. Further, barrier function defects and inflammation have been both associated with several metabolic diseases in dairy cattle and liver abscesses in feedlots. The gastrointestinal tract is sensitive to several factors intrinsic to the productive cycles of dairy and beef cattle. Among them, high grain diets, commonly fed to support lactation and growth, are potentially detrimental for rumen health due to their increased fermentability, representing the main risk factor for the development of acidosis. Furthermore, the increase in dietary starch associated with such rations frequently results in an increase in the bypass fraction reaching distal sections of the intestine. The effects of high grain diets in the hindgut are comparable to those in the rumen and, thus, hindgut acidosis likely plays a role in grain overload syndrome. However, the relative contribution of the hindgut to this syndrome remains unknown. Nutritional strategies designed to support hindgut health might represent an opportunity to sustain health and performance in bovines.

Rumen protected amino acids (RPAA) are increasingly being used in dairy cattle diet formulation to obtain the required concentrations of lysine and methionine in metabolisable protein for optimal milk and milk protein production. The objective of this study was to evaluate the relative bioavailability of a liquid rumen protected lysine prototype using the milk composition technique. Forty mid-lactation Holstein cows were used in a complete randomised block design experiment and allocated to one of four experimental treatments. The treatments were: (1) Methionine deficient (Met-) diet, (2) Met- diet supplemented with Smartamine M (SMM), (3) Met- diet supplemented with liquid rumen protected prototype (LRPMet) and (4) Met- diet supplemented with DL Met (DLMet), a hydroxyl analogue of methionine. After an adaptation phase all four groups received the Met- diet and thereafter switched over to the four treatments. Cows supplemented with SMM had higher milk protein and milk fat % compared to the other treatments and increased milk casein % significantly when compared to the Met-control treatment. The milk protein percentages were 3.06, 3.25, 2.95 and 3.46 and the milk fat percentages 3.84, 3.93, 3.75 and 4.27 for the Met-, LRPMet, DL Met and SMM treatments, respectively. SMM again proved to be the RPAA with a high relative bioavailability, while the LRPMet failed to elicit any milk yield or milk composition response. The milk composition technique proved to be a simple but effective technique to evaluate the bioavailability of rumen protected products or prototypes. Keywords : Milk composition, rumen protected methionine, amino acids, Holstein cows