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

摘要

Our objective was to evaluate the effect of metabolizableprotein (MP) supply on milk production, bloodmetabolites, and health in dairy cows during earlylactation. Three experimental diets were formulatedto contain 114, 107, 101 g of MP/kg of dry matter(DM; 114MP, 107MP, and 101MP, respectively) withcrude protein contents of 17.0, 16.2, and 15.3% of DM,respectively. One hundred multiparous Holstein cowswere fed 1 of these 3 diets during wk 1 to 3 and wk 4to 13 of lactation in one of the following sequences: (1)114MP and 107MP (114MP/107MP), (2) 114MP and101MP (114MP/101MP), or (3) 101MP and 101MP(101MP/101MP). During wk 1 to 3, the 114MPand 101MP treatments were 20 and 27% deficientin estimated MP, respectively. From wk 4 to 13, the114MP/107MP, 114MP/101MP, and 101MP/101MPtreatments were 8, 12, and 13% deficient in estimatedMP, respectively. Data were analyzed separately for wk1 to 3, 4 to 13, and 1 to 13. Dry matter intake andenergy-corrected milk (ECM) yield were not affectedby treatment during wk 4 to 13 or wk 1 to 13; however,ECM yield decreased for 101MP versus 114MP fromwk 1 to 3. Similarly, feed efficiency was not affectedby treatment from wk 4 to 13 or wk 1 to 13, and wasreduced with 101MP versus 114MP during wk 1 to 3.Milk N efficiency tended to increase for 101MP versus114MP for wk 1 to 3 and increased with 101MP/101MPand 114MP/101MP relative to 114MP/107MP duringwk 4 to 13 and wk 1 to 13. Treatment had no influenceon yields and concentrations of milk components fromwk 4 to 13 or wk 1 to 13; however, compared with114MP, feeding 101MP tended to decrease milk fat yieldand decreased yields of milk true protein and lactosefor wk 1 to 3. Both milk and blood urea N concentrationsdecreased for 101MP/101MP and 114MP/101MPrelative to 114MP/107MP during wk 4 to 13 and wk1 to 13, and were reduced with feeding 101MP versus114MP from wk 1 to 3. Treatment had no effect onthe incidence of diseases in cows throughout the study.Serum concentrations of total fatty acids, albumin,and aspartate aminotransferase did not differ between101MP and 114MP; however, serum β-hydroxybutyrateconcentration was lower in cows receiving 101MP duringthe first 3 wk of lactation. Compared with 114MP,feeding 101MP during wk 1 to 3 increased plasmaconcentrations of creatinine and 3-methylhistidine (3-MHis) but did not change the ratio of plasma 3-MHisto creatinine. We found no differences in plasma creatinineor the ratio of 3-MHis-to-creatinine among treatmentsfrom wk 4 to 13; however, 101MP/101MP and114MP/101MP had elevated plasma 3-MHis comparedwith 114MP/107MP. Treatment had no effect on bodyweight and body condition score over the duration of thestudy. Collectively, despite reduced milk production forthe first 3 wk of lactation, feeding the 101MP/101MPtreatment sustained lactational performance and improvedmilk N efficiency without negatively affectingthe frequency of diseases in dairy cows during the first13 wk postpartum.