Effects of high-starch or high-fat diets formulated to be isoenergetic on energy and nitrogen partitioning and utilization in lactating Jersey cows

摘要

The objective of this study was to determine the effectsof high-starch or high-fat diets formulated to beisoenergetic on energy and N partitioning and utilizationof energy. Twelve multiparous Jersey cows (mean± standard deviation; 192 ± 11 d in milk; 467 ± 47 kg)in a crossover design with 28-d periods (24-d adaptationand 4-d collection) were used to compare 2 treatmentdiets. Treatments were high starch (HS; 30.8%starch, 31.8% neutral detergent fiber, and 1.9% fattyacids) or high fat (HF; 16.8% starch, 41.7% neutral detergentfiber, and 4.1% fatty acids). Diets were formulatedto have net energy for lactation (NE_L) content of1.55 Mcal/kg of dry matter according to the NationalResearch Council (2001) dairy model. Nutrient compositionwas varied primarily by replacing corn grainin HS with a rumen-inert fat source and cottonseedhulls in HF. Gross energy content was lower for HS(4.43 vs. 4.54 ± 0.01 Mcal/kg of dry matter), whereasdigestible (2.93 vs. 2.74 ± 0.035 Mcal/kg of dry matter)and metabolizable energy (2.60 vs. 2.41 ± 0.030Mcal/kg of dry matter), and NE_L (1.83 vs. 1.67 ± 0.036Mcal/kg of dry matter) content were all greater thanfor HF. Tissue energy deposited as body fat tended tobe greater for HS (4.70 vs. 2.14 ± 1.01 Mcal/d). ForN partitioning, HS increased milk N secretion (141 vs.131 ± 10.5 g/d) and decreased urinary N excretion (123vs. 150 ± 6.4 g/d). Compared with HF, HS increasedapparent total-tract digestibility of dry matter (66.7 vs.61.7 ± 1.06%), organic matter (68.5 vs. 63.2 ± 0.98%),energy (66.0 vs. 60.4 ± 0.92%), and 18-carbon fattyacids (67.9 vs. 61.2 ± 1.60%). However, apparent totaltractdigestibility of starch decreased for HS from 97.0to 94.5 ± 0.48%. Compared with HF, HS tended toincrease milk yield (19.7 vs. 18.9 ± 1.38 kg/d), milkprotein content (4.03 vs. 3.93 ± 0.10%), milk proteinyield (0.791 vs. 0.740 ± 0.050 kg/d), and milk lactoseyield (0.897 vs. 0.864 ± 0.067 kg/d). In addition, HSdecreased milk fat content (5.93 vs. 6.37 ± 0.15%) butdid not affect milk fat yield (average of 1.19 ± 0.09kg/d) or energy-corrected milk yield (average of 27.2± 1.99 kg/d). Results of the current study suggest thatthe HS diet had a greater metabolizable energy andNE_L content, increased partitioning of N toward milksecretion and away from urinary excretion, and mayhave increased partitioning of energy toward tissue energydeposited as fat.