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Effects of fuels derived from starch digestion on feeding behavior of cows in the postpartum period
Absorbed fuels from the digestion of starch include propionic acid (P) produced by ruminal fermentation and glucose (G) from intestinal digestion that is partially metabolized to lactic acid (L). Our objective was to evaluate effects of these fuels on dry matter intake (DMI) and feeding behavior of cows in the postpartum period. We hypothesized that effects of these fuels on DMI and metabolizable energy intake (MEI) are consistent with their ability to stimulate hepatic oxidation. Little or no G is extracted from blood by the liver. While both L and P are anapleurotic and can stimulate oxidation of acetyl CoA, hepatic extraction of P is greater than L, which depends upon cytosolic redox state. Continuous isoenergetic (150 Kcal/h) infusions of P, L or G were administered abomasally to eight rumen cannulated multiparous Holstein cows (12.4 ± 6.2 DIM) in a duplicate 4x4 Latin Square design experiment balanced for carry over effects. Treatment sequences were assigned to cows randomly. Treatments were control (C, no infusion) and P (99.5%, 0.41 moles/h), L (88.0%, 0.46 moles/h) and G (99.9%, 0.22 moles/h) infused at 500 mL/h for 22 h/d and providing 3.3 Mcal/d. Feeding behavior was recorded by a computerized data acquisition system. Gross energy digestibility of the diet was determined for each cow and used to calculate MEI from the diet. Total MEI was calculated as the sum of MEI from the diet plus energy from infusions. Data were analyzed by ANOVA; the model included random effects of block, cow within block, and period within block and fixed effects of treatment. Treatments were compared with C by preplanned contrasts. Propionic acid decreased DMI by 24.3% (14.3 vs. 18.9 Kg/d, P <0.001) and MEI 13.4%% (34.8 vs. 40.2 Mcal/d, P <0.04) compared with C by tending to decrease meal frequency (P = 0.087). Lactic acid decreased DMI by 13.8% (16.3 vs. 18.9 Kg/d, P < 0.05) compared with C by decreasing meal size 19.8% (P< 0.05) but did not affect MEI. Glucose infusion did not affect DMI or MEI. Treatment effects on DMI and MEI were consistent with their expected effects on hepatic oxidation. Propionic acid production from highly fermentable diets might reduce energy intake of cows in the PP period.
Keywords: anapleurosis, fresh cows, hepatic oxidation