Vitamin D binding factors in bovine blood.

Both 25 [25,26-hydrogen-3] hydroxycholecalciferol and [1alpha,2alpha-hydrogen-3] cholecalciferol were added to bovine plasma in vitro. Analysis by gel-filtration and ion exchange chromatography, electrophoresis, ultracentrifugation, competitive binding specificity studies, and plasma stripping showed that vitamin D circulated with a protein of alpha-globulin mobility. This globulin had a much higher affinity for 25-hydroxycholecalciferol while vitamin D3 appeared to be associated first with an alpha-lipoprotein and with time because associated with the alpha-globulin. This alpha-globulin had a molecular weight of approximately 70,000 as determined by gel-filtration. Cholecalciferol appeared to bind tightly to the alpha-lipoprotein and resisted being stripped from the plasma. Thus, alpha-globulin appears to be the major carrier of vitamin D in the blood while the alpha-lipoprotein may aid in the transfer of cholecalciferol from the gut to the liver via the lymph system.

Changes in plasma 25-hydroxycholecalciferol and selected blood parameters after injection of massive doses of cholecalciferol or 25-hydroxycholecalciferol in non-lactating dairy cows.

Plasma levels of 25-hydroxycholecalciferol, free hydroxyproline, calcium, phosphorus, and magnesium were determined in non-lactating, pregnant dairy cows injected intra-muscularly with 15 X 10(6) IU of cholecalciferol or 25 mg of 25-hydroxycholecalciferol. A lag in the conversion of cholecalciferol to 25-hydroxycholecalciferol was observed in the cows injected with cholecalciferol, while an immediate increase was observed when cows were injected with 25-hydroxycholecalciferol directly. The increased plasma levels of 25-hydroxycholecalciferol following injection of cholecalciferol were directly related to rises in plasma free hydroxy-proline, calcium, and phosphorus, while plasma magnesium was inversely related to plasma 25-hydroxycholecalciferol. Injection of 25-hydroxycholecalciferol caused an immediate increase in plasma calcium which persisted for the duration of the experiment. The biological half-life of 25-hydroxycholecalciferol in the injected cows was found to be 34 days. The data indicate the possibility of a feedback mechanism in which massive doses of cholecalciferol inhibit hydroxylation at the 25ths carbon preventing its conversion to 25-hydroxycholecalciferol until after 8 days post injection. The increase in plasma 25-hydroxycholecalciferol after 8 days resulted in increased bone resorption as indicated by plasma free hydroxyproline.

Milk fever in dairy cows. VIII. Effect of injected vitamin D3 and calcium and phosphorus intake on incidence.

In a field trial, effects of prepartal intermuscular injection of 10 million units of vitamin D3 on incidence of milk fever were examined both in relation to intake of calcium and phosphorous during the dry period and previous history of milk fever. Based upon intake of calcium and phosphorus cooperating herds were grouped as feeding: 1) greater than .53% of the total ration dry matter as calcium and greater than .28% as phosphorus: 2) less than .47% as calcium and greater than .28% as phosphorus; 3) greater than .47% to less than .53% as calcium and greater than .22% to less than .28% as phosphorus. Injections of vitamin D3 given approximately 1 wk prepartum reduced incidence of milk fever in cows with previous history of milk fever in all three groups but had no effect in cows with no previous milk fever. Incidence of milk fever was lower in group 3 than for cows of groups 1 and 2 with previous milk fever and than for cows of group 1 with no previous history. The results indicate that careful control of calcium and phosphorus intake during the dry period at .5% calcium and .25% phosphorus of the dry matter of the total ration will limit milk fever incidence to about 10%. Injections of vitamin D3 as described will reduce inicidence of milk fever further in cows with previous milk fever but not in cows with no previous milk fever.

Milk fever in dairy cows. VII. Effect of continuous vitamin D feeding on incidence of milk fever.

Feeding of 20 to 30 million units of vitamin D for 3 to 8 days prepartum previously prevented about 80% of expected milk fever cases in mature Jersey cows with histories of milk fever. In this experiment vitamin D was fed continuously through the year via 32,000 units of vitamin D added to each .455 kg of concentrate fed (approximately 100,000 to 580,000 units/day). Milk fever incidence was measured after 5 yr of age (third calf) at 43 parturitions in mature Jersey cows with histories of milk fever and at 139 parturitions in mature Jersey cows with no previous milk fever. Continuous feeding of vitamin D reduced incidence of milk fever in cows with previous milk fever from 60% in the controls to 26.1% in the group fed vitamin D. In the cows with no milk fever previously, feeding vitamin D did not reduce incidence of milk fever (controls 23.7%, vitamin-D-fed 28.3%).

Effect of prepartal hormone administration on feed intake and mineral metabolism of cows.

Subcutaneous administration of progesterone (.25 mg/kg body weight per day) to mature cows from 14 days before projected parturition until parturition increased feed intake over control cows. Incidence of milk fever and plasma calcium, phosphorus, magnesium, and hydroxyproline were not significantly different between treated and control cows. Subcutaneous administration of estradiol-17beta (.05 mg/kg body weight per day) or oral administration of melengestrol acetate (1 mg/day) from 7 days before projected parturition date until parturition decreased feed intake over control cows. Milk fever incidence and absorption of calcium, phosphorus, and magnesium were not significantly different between treatment groups. Plasma calcium was not significantly different between treatment groups during either the prepartum or postpartal periods but tended to be higher postpartum in cows treated with estrogen.