Effects of continuous administration of 1,25-dihydroxyvitamin D3 on plasma minerals and unoccupied colon mucosal 1,25-dihydroxyvitamin D3 receptor concentrations

Dose-response effects of an aqueous formulation of calcitriol and evaluation of renal function in nonpregnant cows

Dose responses of plasma calcitriol, calcium (Ca), bone metabolic markers and glomerular filtration rate (GFR) were evaluated in four nonpregnant Holstein cows treated subcutaneously with an aqueous formulation of calcitriol at four doses in a 4 × 4 Latin-square design. Calcitriol, Ca, and markers of bone metabolism were analyzed in plasma samples. GFR was measured in predose and day 5 samples. Plasma calcitriol and Ca concentrations increased dose-dependently. The calcitriol dose was positively correlated with the area under the concentration-time curve of plasma calcitriol. Bone formation markers tended to increase from day 3 onward for all doses. No significant changes in GFR were noted. Thus, exogenous calcitriol administered between 0.0625 and 0.5 µg/kg body weight elicited dose-dependent increases in both plasma calcitriol and Ca and elevated bone formation markers without affecting renal function in nonpregnant cows.

Effects of an oleaginous calcitriol on changes in plasma calcitriol, calcium and bone metabolic markers in dairy cows

The present study evaluated the effects of calcitriol dissolved in an oleaginous vehicle (calcitriol-OLE) on changes in plasma calcitriol, calcium and bone metabolic markers in nonpregnant, nonlactating Holstein cows. Five cows were treated intramuscularly or subcutaneously with calcitriol-OLE and oleaginous vehicle alone using a 5 × 5 Latin square design. Additionally, cows were also treated intravenously with calcitriol dissolved in an aqueous vehicle (calcitriol-AQU) for comparison. The plasma calcitriol concentrations after intramuscular and subcutaneous calcitriol-OLE administrations peaked at 24 and 12 hr, respectively, remained significantly elevated until day 3, returned to the respective control levels on day 5 and decreased significantly on day 7. In cows given intravenous calcitriol-AQU, the calcitriol levels decreased with linearity on day 1. The plasma calcium levels rose from 12 hr post-dose and peaked on day 2 for both preparations and in all three administration routes. Significantly increased calcium levels continued until day 5 in the intramuscular and intravenous routes and day 7 in the subcutaneous route. The plasma osteocalcin concentrations significantly increased from day 3 for calcitriol-OLE and from day 5 for calcitriol-AQU, whereas the bone resorption markers, tartrate-resistant acid phosphatase isoform 5b and hydroxyproline, decreased during this time. These results suggest that either intramuscular or subcutaneous injection of calcitriol-OLE extends and maintains supraphysiological calcitriol levels in the plasma and prolongs hypercalcemia. Moreover, exogenous calcitriol in normocalcemic cows increases the plasma osteocalcin concentration and decreases the plasma levels of bone resorption markers probably due to hypercalcemia.

Application of a reservoir-type calcitriol transdermal patch in dairy cattle

Our objective was to evaluate the effects of a reservoir-type calcitriol (5 mg/animal) transdermal patch on plasma calcitriol and calcium (Ca) concentrations in dairy cattle. A group of six heifers received three different types of patches: an encapsulated reservoir solution containing calcitriol alone (CAL), calcitriol with dodecylamine (CAL+D), or vehicle (CONT). The patches were applied to the skin of the tail for duration of 2 days at intervals of at least 3 weeks. Cattle that received CAL or CAL+D showed significant increases in plasma calcitriol and Ca concentrations on day 2 and days 2 and 3, respectively. The areas under the plasma concentration-time curve (AUC) values for plasma calcitriol and Ca in the CAL and CAL+D groups increased significantly compared to the CONT group. The data of this study describe evidence of measurable transdermal absorption of exogenous calcitriol from a patch and its sufficient biological action to elevate plasma Ca concentrations.

Milk fever and dietary cation-anion balance effects on concentration of vitamin D receptor in tissue of periparturient dairy cows

Milk fever is the clinical disease associated with severe hypocalcemia in dairy cows. In this experiment, we tested the hypothesis that calcium homeostasis is a result of a decreased concentration of receptors for 1,25-dihydroxyvitamin D in the tissues of cows that develop milk fever. Samples of colon mucosa were obtained for analysis of vitamin D receptor concentration in a longitudinal study of Jersey cows during the 2 wk before and after parturition. In the first study, 21 cows fed an alfalfa hay diet were biopsied every 3rd d from 2 wk before to 2 wk after calving. The concentration of vitamin D receptor in the colon during late gestation was three- to fourfold higher than the concentration of vitamin D receptor in the colon mucosa in nonpregnant cows (90 +/- 8 vs. 26 +/- 5 fmol/mg of protein). At parturition, colon concentration of vitamin D receptor decreased to 66 +/- 7.5 fmol/mg of protein. During early lactation, concentrations of vitamin D receptor in the colon were similar to precalving concentrations. There was no significant difference of concentrations of vitamin D receptor in the colon prior to calving, at calving, or in early lactation between cows that did develop milk fever and those that did not. Results were similar in a second study, in which 7 cows were fed a high cation alfalfa diet, and 6 cows were fed the same diet with anionic salts added. Those data do not support the hypothesis that decreased concentrations of vitamin D receptor prior to calving is a causative factor of milk fever within the Jersey breed. However, a decline of concentrations of vitamin D receptor in tissue at calving may reduce the ability of all cows to respond to the calcium demands of lactation.

Acid-base status, renal function, water, and macromineral metabolism of dry cows fed diets differing in cation-anion difference

Dietary cation-anion difference was defined as the summation of the milliequivalents of Na and K minus the sum of the milliequivalents of Cl and S per kilogram of DM. Twelve Holstein cows were used in a crossover experiment to compare the effects of changing the cation-anion difference of a diet based on haylage. Two cation-anion differences, 481.8 and 327.2 meq/kg, were compared. Increased dietary cation-anion difference had no significant effects on BW or intake and digestibility of DM, ADF, NDF, and N. The diet with a cation-anion difference of 481 meq/kg of DM increased apparent absorption of water and urine volume. Fecal excretion of Na and absorption and urinary excretion of S were increased by a cation-anion difference of 327 meq/kg of DM. Although blood concentrations were unaffected, lower dietary cation-anion difference reduced concentrations of H+ and HCO3- in urine and total urinary excretion of HCO3-. Plasma volume, packed cell volume, glomerular filtration rate, and effective renal plasma flow were unaffected by diet. Small changes in dietary cation-anion differences, even within the positive range, affected acid-base status and water metabolism of dry pregnant cows without affecting renal function or blood volume.

Effect of treatment of dairy cows with slow-release bovine somatotropin during the periparturient period on minerals in plasma and milk and on parathyroid hormone-related protein in milk

Slow-release bST was given to dairy cows as a single injection prior to calving to determine whether such treatment prevented parturient hypocalcemia or modified the concentrations of Ca and parathyroid hormone-related protein in milk during the periparturient period. Cows were treated about 1 wk prepartum, and serial blood and milk samples were taken from these and similar prepartum control cows over a 3-wk period. Plasma growth hormone concentrations in the bST-treated group reached a peak 2 d after administration and then declined linearly to control concentrations over a 14-d period. Plasma Ca was unaffected by bST treatment 1 d prior to parturition, on the day of parturition, and at 1 and 6 to 9 d postpartum. Plasma P was higher, and plasma Mg was lower, in the bST-treated group on the day of parturition and 1 d postpartum. Concentrations of Ca, P, Mg, and protein in milk were lower in bST-treated cows than in controls at parturition. Milk production of the bST-treated and control groups was similar when measured at d 6 to 9 postpartum. Concentrations of parathyroid hormone-related protein in milk were substantial at parturition and remained high thereafter, although at parturition the concentration in the milk of the bST-treated group was lower than that of the control group.

Calcium and vitamin D metabolism in the dairy cow

Most dairy cows experience some degree of hypocalcemia during the periparturient period. There is, however, a sub-group of dairy cows that experience a breakdown in their ability to maintain plasma calcium and, consequently, suffer from severe hypocalcemia. This condition is also known as milk fever and usually occurs in cows in their third or greater lactation. The precise metabolic lesions responsible for the onset of milk fever have not yet been defined. Research has shown that milk fever is not the result of inadequate production of calcitropic hormones (parathyroid hormone and 1,25-dihydroxyvitamin D), but rather is more likely a result of inadequate receptor numbers or receptor dysfunction in the target cell of these hormones. This report reviews vitamin D and calcium metabolism, giving emphasis to 1,25-dihydroxyvitamin D receptor regulation and function as related to the periparturient dairy cow. The report also focuses on providing insights into nutritional (anionic diets) and endocrine strategies that have proved useful in milk fever management.

Enzymes and factors controlling vitamin D metabolism and action in normal and milk fever cows

In milk fever (parturient paresis), calcium homeostatic mechanisms, regulated by parathyroid hormone and 1,25-dihydroxyvitamin D, fail to maintain normal blood calcium concentrations, resulting in severe hypocalcemia. The precise nature of the endocrine defect is unknown. Secretion of parathyroid hormone and production of 1,25-dihydroxyvitamin D is similar in most cows with milk fever or without. However, there are some cows that fail to produce adequate 1,25-dihydroxyvitamin D at the onset of lactation. These tend to be cows that will suffer prolonged hypocalcemia and relapse after treatment. Assuming that most cows produce adequate amounts of both hormones, the next logical cause of milk fever might be a failure of tissues to respond to calcium-regulating hormones. Older cows are more likely to develop milk fever than younger ones. We have found that tissue 1,25-dihydroxyvitamin D receptor concentrations decline with age, leaving the tissues less able to respond to 1,25-dihydroxyvitamin D. We also have found that tissue 1,25-dihydroxyvitamin D receptor concentrations increase during pregnancy and lactation in the cow. Intestinal 1,25-dihydroxyvitamin D receptor concentration does not appear to be different in cows with or without milk fever in cows of similar ages. However, intestinal 1,25-dihydroxyvitamin D receptor numbers decrease precipitously at parturition, which may in part be responsible for the development of hypocalcemia in dairy cattle.