ABSTRACT
Sun exposure in bovines is believed to be the most important route of 25D3 synthesis in suitable latitudes. In some situations, e.g. breeding systems, solar radiation cannot reach or penetrate into the skin and thus causes the 25D3 deficiency. Because of the critical effect of vitamin D on the immune and endocrine systems, the plasma must be enriched with 25D3 in a short period of time. In such a condition, injection of Cholecalciferol has been recommended. However, to our knowledge, the certain dose of Cholecalciferol injection for rapid 25D3 plasma enrichment has not been verified. On the other hand, it seems that the basis 25D3 concentration can influence or shift the 25D3 metabolism at the injection time. In the same line, the present study, designed to induce the different basis 25D3 concentration in treatment groups, aimed at investigating the effect of Cholecalciferol intramuscularly injection with the intermediate dose (11,000 IU/kg) on the calves' plasma 25D3 with different basis 25D3. Besides, an attempt was made to clarify the time that 25D3 reaches the sufficient concentration after injection in different treatment groups. To do this, twenty calves of 3 to 4 months old were chosen for the farm with semi-industrial elements. Furthermore, the effect of optional sun exposure/deprivation and Cholecalciferol injection on the 25D3 concentration variations was assayed. To do this, the calves were divided into four groups. Groups A and B were unconstrained to choose sun to expose or shadow in a semi-roofed place, but groups C and D were restricted to the completely dark barn. The interference of the digestive system in supplying vitamin D was minimized through dietary. All groups had a different basic concentration (25D3) on the day 21 of the experiment. At this time, groups A and C received the intermediate dose of (11,000 IU/kg) Cholecalciferol intramuscularly (IM). After Cholecalciferol injection, the effects of basis 25D3 concentration on the details of variation and fate of plasma concentration of 25D3 were investigated. The data collected from the two groups C and D showed that sun deprivation without any vitamin D supplementation, could rapidly and severely deplete the plasma from 25D3. Cholecalciferol injection could not immediately increase the 25D3 in the groups C and A. However, this injection enriches the 25D3 to sufficient value after two weeks if the basis 25D3 of plasma is insufficient, i.e. less than 30 ng/mL. Moreover, the injection of Cholecalciferol could not significantly increase the 25D3 concentration in the group A that had a sufficient basis 25D3 concentration. Therefore, it is concluded that the variation of 25D3 in plasma, after injection of Cholecalciferol, depends on its basic level at the time of injection.
