Reducing metabolizable protein supply: Effects on milk production, blood metabolites, and health in early-lactation dairy cows.

Our objective was to evaluate the effect of metabolizable protein (MP) supply on milk production, blood metabolites, and health in dairy cows during early lactation. Three experimental diets were formulated to contain 114, 107, 101 g of MP/kg of dry matter (DM; 114MP, 107MP, and 101MP, respectively) with crude protein contents of 17.0, 16.2, and 15.3% of DM, respectively. One hundred multiparous Holstein cows were fed 1 of these 3 diets during wk 1 to 3 and wk 4 to 13 of lactation in one of the following sequences: (1) 114MP and 107MP (114MP/107MP), (2) 114MP and 101MP (114MP/101MP), or (3) 101MP and 101MP (101MP/101MP). During wk 1 to 3, the 114MP and 101MP treatments were 20 and 27% deficient in estimated MP, respectively. From wk 4 to 13, the 114MP/107MP, 114MP/101MP, and 101MP/101MP treatments were 8, 12, and 13% deficient in estimated MP, respectively. Data were analyzed separately for wk 1 to 3, 4 to 13, and 1 to 13. Dry matter intake and energy-corrected milk (ECM) yield were not affected by treatment during wk 4 to 13 or wk 1 to 13; however, ECM yield decreased for 101MP versus 114MP from wk 1 to 3. Similarly, feed efficiency was not affected by treatment from wk 4 to 13 or wk 1 to 13, and was reduced with 101MP versus 114MP during wk 1 to 3. Milk N efficiency tended to increase for 101MP versus 114MP for wk 1 to 3 and increased with 101MP/101MP and 114MP/101MP relative to 114MP/107MP during wk 4 to 13 and wk 1 to 13. Treatment had no influence on yields and concentrations of milk components from wk 4 to 13 or wk 1 to 13; however, compared with 114MP, feeding 101MP tended to decrease milk fat yield and decreased yields of milk true protein and lactose for wk 1 to 3. Both milk and blood urea N concentrations decreased for 101MP/101MP and 114MP/101MP relative to 114MP/107MP during wk 4 to 13 and wk 1 to 13, and were reduced with feeding 101MP versus 114MP from wk 1 to 3. Treatment had no effect on the incidence of diseases in cows throughout the study. Serum concentrations of total fatty acids, albumin, and aspartate aminotransferase did not differ between 101MP and 114MP; however, serum β-hydroxybutyrate concentration was lower in cows receiving 101MP during the first 3 wk of lactation. Compared with 114MP, feeding 101MP during wk 1 to 3 increased plasma concentrations of creatinine and 3-methylhistidine (3-MHis) but did not change the ratio of plasma 3-MHis to creatinine. We found no differences in plasma creatinine or the ratio of 3-MHis-to-creatinine among treatments from wk 4 to 13; however, 101MP/101MP and 114MP/101MP had elevated plasma 3-MHis compared with 114MP/107MP. Treatment had no effect on body weight and body condition score over the duration of the study. Collectively, despite reduced milk production for the first 3 wk of lactation, feeding the 101MP/101MP treatment sustained lactational performance and improved milk N efficiency without negatively affecting the frequency of diseases in dairy cows during the first 13 wk postpartum.