The effects of dietary peuNDF-240 and rumen fermentable starch on the milk proteome of dairy cows

The milk proteome is affected by many factors, including diet, and characterizing the impact of diet on the milk proteome can aid in the identification of potential biomarkers that can be used as indicators of cow health and production in dairy systems. The objectives of this study were to 1) identify proteins that were affected by changes in dietary physically effective undegraded neutral detergent fiber (peuNDF-240) and rumen fermentable starch (RFS) levels and 2) determine if milking time affected any proteins due to proximity to feeding. Sixteen Holsteins cows were included in a 4x4 Latin square design experiment, including 4 28-d periods. Cows were milked thrice daily (4:30, 12:30, and 20:30 h). Samples collected from cows receiving two of the diets were analyzed in the current trial: diets were a high peuNDF-240 high RFS diet (HFHS; 8% peuNDF-240, 19.0 ±0.7% RFS) and a low peu-NDF-240 low RFS diet (LFLS; 6.35% peuNDF-240, 16.7±1.0% RFS). Milk samples were collected from each cow during 6 consecutive milkings on d 26-28 of each period. Samples were snap frozen and stored until analysis, and subsequently fractionated for protein isolation. Isolated proteins were quantified and labeled using TMT labels before being analyzed for low abundance proteins using LC-MS/MS. The results were analyzed using PROC MIXED in SAS (v 9.4) to identify the effect of treatment, time, and the interaction of treatment x time. There were 13 proteins identified that were either being affected by time, treatment, and the interaction of treatment x time. Proteins affected by diet, time, or the interaction of diet x time included serpin A3-1, a protease inhibitor, xanthine dehydrogenase/oxidase, which is involved in lipid droplet formation and secretion, and zinc-alpha-2-glycoprotein, which is involved in defense/immunity. Milk proteomics can help to further our understanding of how diet and other factors affect the cow in ways that might not be observed from looking at the cow