PSIX-4 Rumen Microbial Meta-Proteome and Milk Whey Proteome in Holstein Cows fed with High Starch and low Fiber Diet

Identifying milk biomarkers impacted by dietary starch and fiber profiles can support optimization of feeding and concurrent promotion of animal health. The objective of this study was to characterize the rumen meta-proteome and milk whey proteome in Holstein cows fed different levels of physically effective undigestible NDF (peuNDF240) and rumen fermentable starch (RFS). Eight ruminally cannulated Holstein cows were included in a 4 x 4 Latin square design with four 28-day periods. From this study, samples were collected from cows in each period receiving one of two dietary treatments: 1) low peuNDF240, high RFS (LNHR) or 2) high peuNDF240, low RFS (HNLR). Rumen fluid and milk samples were collected at the end of each period at three timepoints, snap-frozen, and stored at -800C. Rumen microbial proteins and milk whey proteins were isolated, quantified, isobarically labeled, and analyzed by LC-MS/MS. The acquired product ion spectra from rumen fluid and the milk samples were searched against 71 composite databases and a cattle database, respectively. Data were analyzed using the PROC MIXED procedure in SAS 9.4. Of the 130 rumen-associated proteins identified across 22 searched microbial species, the abundances of 13 proteins were impacted by diet across eight microbial species. Six of these proteins were associated with core metabolism. Among the 159 quantified milk proteins, the abundances of 17 proteins were impacted by diet. Many of these proteins were associated with host defense, nutrient synthesis, and transportation. The abundance of CD14 and lactadherin was less with the LNHR diet (P < 0.05), whereas Prostaglandin-H2 D-isomerase and lipoprotein lipase abundances were greater with LNHR diet (P < 0.05). Our results indicate feeding a higher concentration of RFS has a greater influence on milk whey proteome than the rumen meta-proteome profile and highlight the potential use of milk whey proteins as biomarkers indicative of nutrition.