Effect of feeding rumen protected rice bran on calcium homeostasis of non-lactating multiparous cows

Milk fever in dairy cows can be prevented by activating Ca homeostasis before calving. Homeostatic adaptation can be achieved by reducing dietary Ca availability. Formaldehyde-treated rice bran was studied to supply rumen protected phytic acid to reduce Ca availability. Twelve multiparous dry cows were used in a 3×3 Latin square change-over design with 5-day periods to test three dietary treatments. Diets consisted of a forage mix (maize silage, grass silage and hay), being 77% of ration dry matter, supplemented with three concentrates: Control (no formaldehyde-treated rice bran), T1 (100% formaldehyde-treated rice bran) and T2 (99.5% formaldehyde-treated rice bran with 0.6% Ca carbonate, to equal Ca content of Control). Dietary treatments did not affect urine pH (8.14, 8.13 and 8.11 for Control, T1 and T2 respectively) or dry matter intake (13.9, 13.7 and 13.8 kg for Control, T1 and T2 respectively). Including formaldehyde-treated rice bran in the diet resulted in lower urinary Ca/creatinine ratio (0.970, 0.457 and 0.618 for Control, T1 and T2 respectively). A sudden increase of urinary Ca excretion took place after withdrawal of T1 and T2 at introduction of Control, peaking on the first day and coming back down progressively in the second and third days. Peak was greatest after T1 and was not observed in transitions between rice bran treatments. This is understood as indirect evidence of activation of intestinal Ca absorption during formaldehyde-treated rice bran feeding, because renal adaptations to changes in blood Ca clearance are immediate and intestinal adaptations delay 2 days. It was concluded that including formaldehyde-treated rice bran in rations before calving may represent a dietary strategy to prevent milk fever without reducing dry matter intake.