Urinary calcium excretion in non-lactating dairy cows in relation to intake of fat-coated rice bran

Abstract

At calving, many older cows fail to compensate the sudden demand of calcium by an adequate activation of intestinal absorption. This results in a variable degree of hypocalcaemia. Reducing intestinal availability of calcium during the close-up period can prevent milk fever. Fat-coated rice bran (FCRB) was investigated for its potential to reduce Ca availability in pre-calving cows. Fat-coated rice bran was incubated in situ to estimate ruminal degradation of dry matter and phytic acid. Also, seven dry multiparous dairy cows were used for a feeding trial in three periods of approximately 1 week each: P1: adaptation; P2: feeding of 2 kg of FCRB and P3: withdrawal of FCRB. Feed intake was recorded and daily urine samples were analysed for pH, Ca and creatinine. The bypass fraction of phytic acid (passage rate: 5%/h) was 30%. Fat-coated rice bran depressed dry matter intake in P2, resulting in a lower Ca intake. In P2 urine pH and calcium excretion were lower. Daily calcium excretion decreased after introduction of FCRB, peaked after withdrawal and dropped 2 days later. Changes in urinary Ca excretion by feeding FCRB indicate that FCRB affected Ca homeostasis in dry multiparous dairy cows.

A novel model to explain dietary factors affecting hypocalcaemia in dairy cattle

“…The rapid adaptation of renal reabsorption and delayed adaptation of intestinal absorption can explain the increases in urinary Ca excretion observed by our group in cows for 2 d after the withdrawal of a restriction in dietary Ca availability (29,32) . Urinary excretion of Ca is an effective means to correct positive fluctuations in blood Ca (1) .…”

“…In rats, this adaptation has been proven to take longer than 1 d to take effect (31) . To our knowledge, this delay has not been directly observed in cattle; however, we have observed indirect indications of this delay by monitoring urinary Ca in cows, which suggest that the inactivation of gastrointestinal Ca absorption may present a 2 d delay (29,32) . Furthermore, calcitriol sustains bone Ca mobilisation, offering an extensive pool for sustaining Ca homeostasis during lactation (33) ; however, in the short term, the readily available bone Ca is limited (34) .…”

“…Phytic acid in rice bran can be protected from ruminal degradations by different treatments (29,116) .…”

“…During the Ca deficit, the homeostatic system can reduce the urinary excretion to urinary Ca losses that are as low as 0·1 mmol Ca per g creatinine (29) (approximately 0·07 g/d). The aim of this simulation is to predict whether a Ca imbalance can induce this and other adaptive reactions.…”

“…Rumen-protected rice bran can induce the adaptation of Ca metabolism in cows (29) . This effect is caused by very low Ca content and the action of lowering the dietary availability of Ca (32) .…”