Interactions of protein levels fed to Holstein cows pre- and postpartum on productive and metabolic responses

摘要

The objective of this study was to examine the interactionbetween levels of dietary crude protein (CP)pre- and postpartum on feed intake, performance, andmetabolic status of dairy cows with a 14-d close-upexperimental period. Forty multiparous Holstein cowswere blocked by expected calving date and previouslactation milk yield at −14 d relative to expected calvingand randomly allocated to receive either a 12.5%CP diet with 3.3% rumen undegraded protein (RUP;12pre) or a 15.2% CP diet with 5% RUP (15pre) basedon dry matter (DM). From d 1 to 21 postpartum, cowswithin each prepartum group were randomly assigned toreceive either a 16.1% CP diet with 4.9% RUP (16post)or a 18.6% CP diet with 6.8% RUP (19post) basedon DM. The experiment was conducted as a split-plotdesign, with CP prepartum being the whole-plot factorand CP postpartum as the subplot factor. Dietswere similar in net energy for lactation, and CP levelswere increased by replacing grain with a combinationof corn gluten meal and fish meal. In prepartum, cowsfed the 15pre diet tended to consume more DM thancows fed the 12pre diet (9.65 vs. 9.30 kg/d). Exceptfor blood urea nitrogen (BUN) concentration, no otherblood metabolite in prepartum was affected by diets.The interaction between pre- and postpartum CP levelsshowed that elevating dietary CP from 16post to19post increased DM intake (15.20 vs. 17.67 kg/d) andmilk yield (35.16 vs. 40.26 kg/d) in 12pre cows but notin 15pre cows. Milk fat, protein, and lactose contentswere not affected by the interaction between pre- andpostpartum CP levels. Feeding 19post compared with16post increased milk protein (1.28 vs. 1.08 kg/d) andlactose (1.86 vs. 1.61 kg/d) yields in 12pre cows, whereasthis effect was not observed in 15pre cows. Milk ureanitrogen was elevated when dietary CP increased from16post to 19post in 15pre cows (12.98 vs. 14.84 mg/dL)but not in 12pre cows. The concentrations of BUN weregreater in 19post cows than in 16post cows for both12pre (16.31 vs. 13.81 mg/dL) and 15pre (18.44 vs.14.71 mg/dL) cows. The 19post cows had lower serumfatty acids than 16post cows (0.65 vs. 0.96 mmol/L) in12pre but not in 15pre. However, a reduction in serumaspartate aminotransferase (AST) concentration wasobserved in 19post cows compared with 16post cows(68.30 vs. 98.24 U/L) when cows were fed 12pre. Forcows fed 15pre, those fed 19post had higher serum ASTlevels than those fed 16post (86.61 vs. 67.74 U/L) during21 d of lactation. Body weight and body conditionscore changes were not affected by interactive effectsbetween pre- and postpartum CP levels, but 19postcows tended (−0.30 vs. −0.45) to have smaller bodycondition score losses than 16post cows when fed the12pre diet. Overall, increasing dietary CP postpartumfrom 16 to 19% DM improved performance and metabolicstatus of cows fed 12% CP prepartum. The lackof responses to increased dietary CP postpartum incows fed 15% CP prepartum suggests that dietary CPpostpartum could decrease to 16% DM when cows arefed higher dietary CP prepartum.