An interest in vitamin D3 and its metabolite roles has released an explosion of new information in relation to the animal nutrition and physiology. In general, vitamin D3 deficiency considerably affects phosphorus and calcium metabolism. Its inadequacy can result in calcium, phosphorus and magnesium changes in blood plasma, Simultaneously the activity of alkaline phosphatase is being increased. The new vitamin D3 research also showed that the most active metabolite of vitamin D3 acted in non-specific immunoreactions (Ammenudin, 1985; Porsova, 1987). Biological efficiency of two Czech vitamin D3 supplements (feeding coated forms) from VUOS Pardubice in comparison with those produced by Jerevan Vitamin Co. and Hoffmann La Roche Co. (positive control) was studied. The present study (two experiments with broilers) was conducted to obtain information on plasma Ca and P levels and AP activity at the age of 27 and 56 days. Some white blood count values were also measured. Two experiments were performed on Hybro broiler chickens. The chickens were randomly alloted to five groups of sixty each. The groups were fed a rachitogenic diet ad libitum; vitamin D3 supplements were added to feed additive premixes. There was also a negative control in both trials (Tab. 1). Plasma Ca, P and AP concentrations were assayed using Bio-La Test Lachema Brno Total and differential leucocyte counts were performed according to the technique described by Natt and Herrick (1955), Data were analysed by analysis of variance; significant differences between treatment means were determined by Duncan's multiple range test. Plasma biochemical parameters are shown in Tab. II. Plasma Ca and P concentrations and AP activity ranged from 2.7 to 6 mmol/l, 1.1 to 2.3 mmol/l and 13.3 to 24.3 mukat/l, respectively. No significant difference between the groups was confirmed during the study of Ca and P plasma levels. This observation corresponds with the results reported by Leeson and Summers (1988) and Bootwalla et al. (1989). We assessed only significantly higher Ca plasma concentrations in 56 days old chickens. It is assumed that it was due to the high feed consumption in this period. AP activity was significantly higher in the negative control, which is in accordance with Lopuchovsky (1964), Ameenudin et al. (1985), Friedrich (1988). The results of total and differential leucocyte counts are shown in Tabs. III and IV. The number of leucocytes ranged from 20 to 43 (3/1. The higher values were obtained at the age of 28 days. The counts of monocytes were higher in all chickens. The increase in monocyte counts influenced by the addition of vitamin D3 which was described by Aminenudin et al. (1985) and Porsova (1987) was not confirmed. As to the vitamin D3 effect, the white blood count changes were not significant. The obtained biochemical and haematological profiles suggest that all vitamin D3 supplements were comparable.
