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چکیده
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The objective of this study was to examine the interaction between the levels of dietary CP pre- and postpartum on feed intake, performance, and metabolic status of dairy cows with a shortened close-up period . Forty multiparous Holstein cows were blocked by expected calving date and previous lactation milk yield at -14 days prior to expected calving and randomly allocated to receive either a 12.5% CP diet with 3.3% RUP (12pre) or a 15.2% CP diet with 5% RUP (15pre) based on dry matter (DM). From d 1 to 21 postpartum, cows within each prepartum group were randomly assigned to receive either a 16.1% CP diet with 4.9% RUP (16post) or a 18.6% CP diet with 6.8% RUP (19post) based on DM. The experiment was conducted as a split-plot design, with CP prepartum being the whole-plot factor and CP postpartum as the subplot factor. Diets were similar in net energy for lactation and CP levels were increased by replacing grain with a combination of corn gluten meal and fish meal. In prepartum, cows fed 15pre diet tended to consume more DM than cows fed 12pre diet (9.65 vs. 9.30 kg/d). Except for blood urea nitrogen (BUN) concentration, no other blood metabolite in prepartum was affected by diets. The interaction between pre- and postpartum CP levels showed that elevating dietary CP from 16post to 19post increased DMI (15.20 vs. 17.67 kg/d) and milk yield (35.16 vs. 40.26 kg/d) in 12pre cows, but not in 15pre cows. Milk content of fat, protein, and lactose were not affected by the interaction between pre- and postpartum CP levels. Feeding 19post relative to 16post increased milk protein (1.28 vs. 1.08 kg/d) and lactose (1.86 vs. 1.61 kg/d) yields in 12pre cows, whereas this effect was not observed in 15pre cows. Milk urea nitrogen was elevated when dietary CP increased from 16post to 19post in 15pre cows (12.98 vs. 14.84 mg/dL), but not in 12pre cows. The concentrations of BUN were greater in 19post cows than 16post cows for both 12pre (16.31 vs. 13.81 mg/dL) and 15pre diets (18.4
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