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Mulakala, Bharath Mulakala

Animal and Veterinary Sciences

2023

Ph. D.

Dietary fiber and starch content influence rumen function and ultimately impact cow health and productivity. However, little information is available assessing the influence of dietary carbohydrate profiles on rumen microbial metabolic activity and the rumen epithelial transcriptome. Further, biomarkers indicative of rumen function and health are scarce but could be useful in optimizing nutritional efficiency. The first objective was to characterize the rumen meta-proteome in cows fed different dietary contents of physically effective undegradable neutral detergent fiber (peuNDF240) and rumen fermentable starch (RFS). Eight cannulated Holstein cows were assigned to the study as part of a 4 x 4 Latin square design with a 2 x 2 factorial treatment arrangement, including four 28-d periods. Cows received one of four dietary treatments (dry matter basis); 1) low peuNDF240, low RFS, 2) high peuNDF240, low RFS, 3) low peuNDF240, high RFS, and 4) high peuNDF240, high RFS. The microbial protein fraction was isolated from rumen fluid samples collected from each cow on d 27 and 28 in each period and analyzed using LC-MS/MS techniques. The product ion spectra obtained from the samples were searched against 71 curated microbe-specific databases. Out of 46 proteins that were affected by treatments, 28 proteins across 13 microbial species were influenced due to RFS content in the diet, indicating RFS content of the diet has a greater influence on rumen microbial protein abundances. To evaluate the use of milk proteins as indicators of changes in rumen microbial activity resulting from dietary carbohydrates, rumen fluid and milk samples were collected from the cows that received either the high peuNDF240, low RFS, or low peuNDF240, high RFS diet on the last two days in each period. Isolated proteins within each rumen fluid or milk sample were isobarically labeled and analyzed by LC-MS/MS. These results indicated that milk lipoprotein lipase (LPL) concentration may be a feasible milk biomarker indicative of an altered rumen environment. The last objective was to examine the impact of the intra-ruminal dosage of propionate on the rumen epithelial transcriptome profile. Four ruminally-cannulated Holstein lactating were included in 2 x 2 crossover design and received an intra-ruminal dosage of either Na propionate or NaCl at 1 % and 0.6 % of dry matter intake, respectively. Rumen fluid, milk, and blood samples were collected from each cow on d 5, 6, and 7. Rumen epithelial biopsies were collected on d 7 from each cow in each period. Propionate treatment resulted in 331 differentially expressed genes in cow rumen epithelium. The results indicate that propionate dosage altered the expression of rumen epithelial genes involved in protein metabolism, cell growth and division events, lipid transport and metabolism, immune function, and transport activity, indicating major biological processes response triggered in response to an altered rumen environment. Cumulatively, the results of this research indicate that dietary carbohydrate profile impacts rumen microbial protein abundances. In addition, diet-induced ruminal changes altered the rumen epithelial transcriptome and milk protein profile. The results of this research highlighted the use of milk proteins as a biomarker for altered rumen environment, particularly milk LPL concentration as an indicator for diet-induced ruminal changes.