Effects of glucose infusion on feed intake, milk production, and metabolic responses of early postpartum cows fed a high starch or high protein diet were evaluated utilizing a randomized complete block design experiment with a 2x2 factorial arrangement of treatments. Twenty-four multiparous Holstein cows were blocked by BCS and 305-ME milk production, and randomly assigned at parturition to one of four treatments. Treatments were continuous intrajugular infusion of glucose (GI; 4 L/d of 25% w/v dextrose) or isotonic saline (SI; 4 L of 0.9% sodium chloride), and diets containing high starch/low crude protein (HSLP) or high crude protein/low starch (HPLS) concentration. Treatments were initiated at the first feeding following parturition and lasted 12 d. GI, compared with SI, reduced cumulative DMI for HPLS (164.0 vs. 196.5 kg) but not HSLP (194.2 vs. 189.7 kg; interaction P = 0.04) by reducing meal size for HPLS (13.6 vs. 16.4 kg) but not HSLP (16.4 vs. 15.9 kg; interaction P = 0.14). HPLS increased plasma concentrations of NEFA (1184 vs. 895 μEq/L, P = 0.01) and BHBA (13.0 vs. 9.5 mg/dL, P = 0.03), liver triglyceride (5.7 vs. 3.5 mg/g wet liver, P = 0.03), milk fat concentration (5.71 vs. 4.72%, P < 0.01) and yield (2.14 vs. 1.78 kg/d, P < 0.01) and 3.5% fat-corrected milk (50.9 vs. 45.1 kg, P = 0.02), and tended to increase body condition loss (-0.82 vs. -0.65 BCS units/12 d, P = 0.06) compared with LPHS. HPLS increased BCS loss despite no difference in plasma insulin between dietary treatments (P = 0.23). The HPLS diet and GI interacted to reduce meal size and feed intake, possibly by affecting hepatic oxidation of fuels.
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