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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.

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