Aspects of physiological effects of sodium zeolite A supplementation in dry, non-pregnant dairy cows fed grass silage.

The objective of the present study was to monitor serum and urine biochemical changes in dairy cows during and after oral administration of a synthetic sodium aluminium-silicate (zeolite A). A prospective longitudinal study involving four non-pregnant and non-lactating cows was chosen. Cows were randomly allocated to either a control or experimental group. The period of observation was three weeks. During the first week (period 1) cows were maintained on basic ration for the purpose of recording baseline values. During the second week (period 2) control cows were fed a basic diet (grass silage), while cows in the experimental group were fed the basic diet and supplemented with 1 kg zeolite pellets once daily. During the third week (period 3) both groups were fed the basic ration only and observed for any persistent effects after zeolite withdraw. Daily sampling included blood and urine. Selected physiological parameters were compared between groups during period 2 and 3, whereas mean values from period 1, 2 and 3 were compared within the groups. Zeolite supplementation revealed a significant influence on calcium homeostasis. A slight decrease in serum Ca and in renal excretion of calcium was observed in the experimental group at initiation of supplementation, whereas an increment in these parameters was recorded after withdrawal of zeolite supplementation. It is assumed, that zeolite caused a reduction in the availability of dietary calcium during supplementation, which possibly elicited an activation of calcium mobilisation. The influence of zeolite on calcium homeostasis was not evident from monitoring serum concentration of calcium regulating hormones (PTH, 1,25(OH)2D3, 25(OH)VitD) or renal excretion of markers of bone resorption. Enhanced active intestinal calcium absorption and bone resorption was therefore considered insignificant in the calcium mobilisation under the conditions of this experiment. The origin of the increased amount of Ca, which was observed in serum and urine after zeolite withdraw, is at present unknown, but it is suggested, that the readily mobilized Ca-pool in bone was a contributing factor. An effect of zeolite on phosphate and magnesium homeostasis in the experimental group was evidenced from the values of serum concentration and fractional excretion, which during supplementation were significant lower than in the control group. The influence of zeolite on phosphorus and magnesium is presumed to result from a combination of interference of zeolite with intestinal absorption and a marginal dietary supplementation of these minerals.