The effect of fructose infusion on dry matter intake in dairy cattle

Abstract Text:

Loading of fructose or its analogues in mammals resulted in the accumulation of fructose 1-phosphate in the liver, sequestering organic phosphate (Pi), preventing ATP production, and most likely as a consequence, increasing feed intake. The objectives of this work were to determine the effects of fructose and Pi infusions on feeding behavior of dairy cows in order to link hepatic ATP synthesis and feeding behavior and better understand the mechanisms controlling feed intake. Eight Holstein cows from 4-8 days postpartum (PP) were used in a duplicated 4X4 Latin square design experiment with one block each of multiparous and primiparous cows. Periods were 24 h, including 2 h infusions and 22 h recovery period. Treatments were arranged in a 2x2 factorial with fructose and Pi infusions as main effects. Cows were infused through a jugular catheter with 0.6 mol/h of fructose or glucose and 0.3 mol/h of NaCl or NaH₂PO₄. Effects of treatment on DMI were analyzed by ANOVA with repeated measures. Both fructose and Pi had hyperphagic effects; fructose increased DMI by 23.11% in the first 0.5 h of infusion compared with glucose (4.16 vs. 3.38 kg, P<0.01) but the effect diminished over time with no effect detected by 1 h following the start of infusion. An interaction was detected between Pi and block (P=0.06); NaH₂PO₄ increased DMI over the 2 h infusion period by 36.9% compared with NaCl for multiparous cows (8.41 vs. 6.14 kg, P<0.001), but did not affect DMI for primiparous cows. Although effects of fructose on DMI hints at a connection between ATP synthesis and intake, Pi infusion was expected to reduce the effect of fructose by providing Pi for ATP synthesis rather than increasing intake. It is possible that the infused phosphate did not enter the liver and therefore did not have the expected effect. Reducing dietary P is essential in order to limit P excretion. Previous works showed that feeding P levels similar to this work (0.37% of DM) does not reduce DMI; however, such level might be insufficient specifically for cows in the PP period. Accordingly, further research to understand the hyperphagic effect of Pi might have implications for diet formulation for cows in the PP period. Better understanding the effects of Pi and fructose on hepatic ATP synthesis should provide insights on the connection between ATP synthesis and feeding behavior in dairy cows.

Keywords: Fructose, Phosphate, DMI.