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Absorption of glucose from the gastrointestinal tract of cows is very low because the microbial flora of the forestomach readily converts glucose to acetic, propionic and butyric acids. Therefore dairy cows mainly use acetic and butyric acids for lipogenesis. This study aimed to determine how key lipogenesis enzymes of dairy cows adapt to an artificially increased glucose supply by the intravenous route.
Mid-lactating Holstein-Friesian Cows were either infused intravenously with 40% glucose solution or volume-equivalent 0.9% saline solution. The glucose dose increased daily by 1.25% of the calculated net energy (NEL) requirement, reaching 30% NEL requirement (~ 2.65 kg glucose/d) on day 24. At dose levels of 0%, 10%, 20% and 30% NEL, relative gene expression and enzyme activity of key lipogenesis enzymes were determined in adipose tissue biopsies.
Linear dose x treatment interactions were observed for the relative gene expression of fatty acid synthase (FAS), glycerol-3-phosphate dehydrogenase (G3PD) and glucose-6-phosphate dehydrogenase (G6PD) with increasing expression at increasing levels of glucose infusion. Simultaneously, enzyme activity of FAS showed linear dose x treatment interaction with highest FAS activity at a dose level of surplus 30% NEL in the glucose-infused group. Activities of G3PD and G6PD did not change significantly.
Cows adapt to a surplus supply of glucose with increased expression and activity of FAS to increase lipogenesis in adipose tissue. Supported by Pfizer Animal Health