The effect of dose rate of 1-alpha-hydroxycholecalciferol on calcium and phosphorus metabolism in sheep

Effects of lα-hydroxylated metabolites of cholecalciferol on intestinal radiocalcium absorption in goats

1. Intestinal absorption of47Ca was measured by a double-isotope technique in goats treated with 1, 5 or 25 μg of 1,25-dihydroxycholecalciferol (1,25(OH)2D3). The effects of giving 1,25(OH)2D3by intravenous (iv) infusion for 30–36 h were compared at each dose level with the effects obtained by oral administration of 1,25(OH)2D3either in ethanol or protected against rumen degradation in fatty acid pellets.

2. Dose-dependent increments in absorption followed the treatments, with a doubling of absorption at the 1 μg dose and three- to fivefold increases with the 5 and 25 μg doses.47Ca absorption was equally stimulated 2 and 6 d after treatment but had returned to pretreatment levels 12–14 d after treatment.

3. Intravenous and protected oral administration of 1,25(OH)2D3stimulated47Ca absorption to the same extent, in spite of two- to fivefold higher plasma concentrations of 1,25(OH)2D3after iv treatment. Somewhat lower increments in47Ca absorption were seen using ethanol as the vehicle for oral administration.

4. The naturally occurring metabolites 1,24(R),25-trihydroxycholecalciferol and 1,25(S),26-trihydroxy-cholecalciferol had only one-tenth to one-fifteenth the potency of 1,25(OH)2D3in stimulating47Ca absorption, while synthetic lα-hydroxycholecalciferol appeared to be twice as effective as 1,25(OH)2D3when tested at a high (10μg) dose.

Phosphorus partitioning during early lactation in dairy cows fed diets varying in phosphorus content

The effect of dietary P content on P partitioning and excretion during early lactation was evaluated in 13 cows fed diets containing 0.34 (no supplementary P), 0.51, or 0.67% P. All cows were fed a common pre-partum total mixed ration (TMR) (0.28% P), followed by common TMR (0.51% P) for 7 d post-partum. On day 7, cows were randomly assigned to one of the three dietary P treatments. All treatment diets contained 16.6% CP, 15.2% ADF, 26.3% NDF, and 0.74% Ca. Total collections of milk, urine, and feces were conducted during weeks 3, 5, 7, 9, and 11 of lactation. Average body weight (591 kg), milk yield (47.9 kg/d), and DMI (25.2 kg/d) throughout the 10-wk trial were not affected by dietary P content. With increasing dietary P, however, linear increases in P intake (84.7, 135.2, and 161.5 g/d), fecal P (42.3, 87.5, and 108.6 g/d), urinary P (0.32, 1.28, and 3.90 g/d), and total P excretion (42.6, 88.8, and 112.5 g/d) were observed. Apparent P digestibility (49.0, 34.4, and 32.8% of P intake) decreased quadratically with increasing dietary P. Phosphorus balance was highly variable, but cows fed the 0.34% P diet were in negative P balance longer than were cows fed diets containing 0.51 or 0.67% P. With increasing dietary P, serum concentrations of inorganic P increased linearly, but serum Ca and Mg concentrations decreased. Increasing dietary P increased fecal and urinary P excretion in early lactation cows. Increased duration of negative P balance and changes in blood mineral concentrations suggest that cows fed low P diets mobilized more P from body reserves than cows on medium- and high-P diets.

1 alpha-hydroxyvitamin D3 plus 25-hydroxyvitamin D3 reduces parturient paresis in dairy cows fed high dietary calcium

The effectiveness of a combination of 1 alpha-hydroxyvitamin D3 and 25-hydroxyvitamin D3 for reducing incidence of parturient paresis in aged Holstein cows was tested. Intramuscular injection of .5 mg of 1 alpha-hydroxyvitamin D3 plus 4 mg of 25-hydroxyvitamin D3 increased plasma 1,25-dihydroxyvitamin D concentrations through parturition. Treatment with 1 alpha-hydroxyvitamin D3 plus 25-hydroxyvitamin D3 raised prepartum serum Ca approximately 2 mg/dl and prepartum serum P approximately 4 to 5 mg/dl higher than untreated controls. Both treated and control cows had approximately a 2-mg/dl decrease in serum Ca following parturition. The prepartum diet of alfalfa silage and hay was supplemented with a grain mixture supplying 100 g of Ca/d from ground limestone. Under these dietary conditions, incidence of parturient paresis was reduced from 33 to 8%. In a separate experiment, treatment with 1 alpha-hydroxyvitamin D3 plus 25-hydroxyvitamin D3 did not reduce incidence of parturient paresis when cows consumed mixed diets of different feed-stuff composition. Further experiments are required to determine specifically the factor or factors responsible for the difference in response to active vitamin D compound administration between the two experiments. Prepartum dietary Ca intake may be one such factor.

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

Six mature nonlactating, nonpregnant Jersey cows were implanted with Alzet mini-osmotic pumps, which delivered 50 micrograms of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] each day for 7 d in an effort to mimic plasma concentrations of 1,25-dihydroxyvitamin D [1,25-(OH)2D] observed in cows at parturition. Plasma samples were obtained daily beginning 6 d prior to implantation and ending 8 d after removal of the implants. Six biopsies of the descending colon mucosa were obtained per rectum before and after implantation and assayed for unoccupied 1,25-(OH)2D3 receptor concentration. Plasma concentration of 1,25-(OH)2D increased from 37 pg/ml pretreatment to 294 pg/ml with the pumps implanted. Plasma Ca concentration increased within 2 d after implantation and remained elevated for 7 d after the pumps were removed. Unoccupied colon mucosa 1,25-(OH)2D3 receptor mean concentration prior to treatment was 14.6 fmol/mg protein and increased within 2 d following implantation to 30.5 fmol/mg protein. These data suggest that 1,25-(OH)2D3 upregulates its own receptor in the intestine of the cow.

Use of 1 alpha-hydroxyvitamin D3 in prevention of bovine parturient paresis. 8. Maternal and neonatal plasma calcium, parathyroid hormone, and vitamin D metabolites concentrations

Thirteen Israeli Friesian cows (3.71 average calvings) in the second or later lactation, fed a daily diet containing 90 g of Ca and 50 g of P, were injected once intramuscularly with 700 micrograms 1 alpha-hydroxy-vitamin D3 in order to investigate its placental transfer and its subsequent metabolism in the neonate. The injection of the vitamin 96 to 24 h before calving slightly increased plasma Ca at parturition, whereas uninjected controls displayed a prominent hypo-calcemia. On the 10th and 20th d after calving, difference in the plasma Ca concentration of the two groups was not significant. At parturition, plasma parathyroid hormone concentration was significantly higher and plasma 1,25-dihydroxyvitamin D lower in the control than in the treated cows. At parturition the plasma concentrations of Ca, parathyroid hormone, hydroxyproline, and 24,25-hydroxyvitamin D were higher in the calves than in their dams. Plasma concentrations of 25-hydroxyvitamin D were markedly higher and 1,25-hydroxyvitamin D was slightly higher in cows than in their offsprings.

Use of 1 alpha-hydroxyvitamin D3 in the prevention of bovine parturient paresis. IX. Early and late effects of a single injection

Israeli Friesian cows in the third or later lactation were injected intramuscularly (serratus muscle of the neck) with 1 alpha-hydroxyvitamin D3 in propylene glycol in order to compare the short-term and long-term effects of the drug. Following injection of 700 micrograms 1 alpha-hydroxyvitamin D3, the D-derivative appeared in the plasma after 12 h and reached a peak 24 h after injection. Plasma 1,25-dihydroxyvitamin D increased as early as 6 h and peaked at 24 h. Plasma calcium increased after 6 h and peaked 4 to 5 d after the injection. The administration of a single dose of 350 micrograms 1 alpha-hydroxyvitamin D3 at 7 to 8 d before calving did not prevent periparturient hypocalcaemia observed in the uninjected control cows. A single injection of 700 micrograms 1 alpha-hydroxyvitamin D3 7 to 8 d before parturition prevented hypocalcemia at calving. There were no significant differences in plasma calcium 4 to 21 d after calving between the injected and control cows nor were there any cases of delayed postparturient hypocalcemia or milk fever. Results suggest that 700 micrograms 1 alpha-hydroxyvitamin D3 prolonged the calcemic effect of the drug and prevented hypocalcemia at parturition, even if administered 6 to 8 d before calving.

Effect of 1,25 dihydroxyvitamin D3 on the calcium and magnesium metabolism of lactating cows

Administration of 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) to lactating dairy cows resulted in increased dietary calcium absorption and elevated concentrations of plasma calcium. Dietary magnesium absorption was unaffected by 1,25(OH)2D3 however, plasma magnesium concentration was depressed. Injections of 1,25(OH)2D3 were effective in elevating plasma calcium concentrations in both normal and hypomagnesaemic cows. This indicates a potential use for 1,25(OH)2D3 to prevent and treat hypocalcaemic cows with or without concurrent hypomagnesaemia.

Observation on the use of 1 alpha-hydroxyvitamin D3 in the prevention of bovine parturient paresis: the effect of a single injection on plasma 1 alpha-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, calcium, and hydroxyproline

Israeli Friesian cows in the third or later lactation, were injected intramuscularly with 1 alpha-hydroxyvitamin D3 in propylene glycol. Plasma 1 alpha-hydroxyvitamin D3 peaked 24 to 48 h after 700 micrograms of the drug was injected and decreased to the initial concentration 4 d later. The disappearance rate of 1 alpha-hydroxyvitamin D3 from the blood was .330 d-1 (biological half-life of 2.1 d). Plasma 1,25-dihydroxyvitamin D3 peaked 24 to 48 h after the injection and approached the initial concentration 5 to 7 d later. Plasma calcium increased within 24 h, reached a plateau at 4 to 6 d, and then decreased. Administration of 700 micrograms 1 alpha-hydroxyvitamin D3 resulted in higher plasma 1,25-dihydroxyvitamin D3 and calcium concentrations than when 350 micrograms of the drug was injected. 1 alpha-Hydroxyvitamin D3 did not affect plasma hydroxyproline. The injection of 700 micrograms 1 alpha-hydroxyvitamin D3 52 to 36 h before parturition resulted in a greater increase in plasma 1,25-dihydroxyvitamin D3 than that obtained with 350 micrograms. In both groups 1,25-dihydroxyvitamin D3 peaked 24 h after injection, as opposed to the controls, which peaked 72 h postpartum. At parturition, the 700-micrograms dose resulted in a slight hypercalcemia; the 350-micrograms dose moderated the hypocalcemia prevalent during this period, whereas in controls hypocalcemia was more pronounced. In cows injected with 700 micrograms, hypercalcemia was observed until the 15th d postpartum. Plasma hydroxyproline was elevated in all cows 48 to 72 h after parturition, but the increase was smaller in animals injected with 1 alpha-hydroxyvitamin D3.(ABSTRACT TRUNCATED AT 250 WORDS)

1,25 dihydroxyvitamin D3 increases plasma magnesium and calcium in sheep fed liquid diets low in calcium and magnesium

Sheep given a liquid diet low in calcium and magnesium by infusion directly into the abomasum developed concurrent hypocalcaemia and hypomagnesaemia, with plasma concentrations of calcium and magnesium decreasing to 2.0 and 0.4 mmol/l respectively. Treatment of these hypomagnesaemic sheep with 1,25 dihydroxyvitamin D3 (1,25(OH)2 D3) increased the plasma calcium, magnesium and phosphorus concentrations with plasma calcium increasing to 2.5 mmol/l and plasma magnesium to 0.6 mmol/l. Plasma magnesium increased despite a small but significant increase in the daily excretion of magnesium in the urine, and the amount of magnesium derived from either bone and/or intestine must have been greater than the amount lost in the urine. Since in other experiments we have demonstrated that plasma calcium remains within the normal range when a liquid diet adequate in magnesium but low in calcium is infused, these results imply that either synthesis of and/or end organ response to 1,25(OH2) D3 is impaired in magnesium deficient sheep.

Calcium and phosphorus requirements of the ewe during pregnancy and lactation. 2. Phosphorus

Mineral balance and radioisotope studies have been carried out to test the adequacy of the recent Agricultural Research Council (1980) recommendations for calcium and phosphorus for pregnant and lactating ewes. At the same time, P metabolism was compared throughout pregnancy and lactation in ewes fed according to these recommendations and in ewes fed a plentiful supply of dietary Ca and P. Bone mineral stores were mobilized in late pregnancy and early lactation, irrespective of the rate of P absorption. These stores were then replaced in mid- to late lactation in ewes given the plentiful Ca and P intake but not in the ewes given the restricted intake. Results suggest that these changes in bone stores occurred as a result of changes in Ca requirements rather than in P requirements, and that accretion of P into bone or resorption of P from bone occurred merely as a consequence of this change in Ca requirements. Immediate demands for P for maintenance and fetal or milk production do not reflect net P demands, which also take into account changes in bone P metabolism. The rate of P absorption was directly related to net demands and the rate of endogenous excretion was inversely related to net demands. Absorption and endogenous faecal loss of P were also both directly related to P intake. A lack of dietary Ca, particularly in mid- to late lactation, makes it impossible to draw conclusions on the adequacy of the Agricultural Research Council (1980) recommendations for P. Results do suggest, however, that P requirements ought to be calculated according to net demands for P rather than immediate demands.

The effect of 1 alpha-hydroxycholecalciferol on the placental transfer of calcium and phosphate in sheep

The calcium and phosphorus concentrations in foetal tissue or the placental transfer of 45Ca and 32P, or both, were studied in fifty-five control or 1 alpha-hydroxycholecalciferol (1 alpha-(OH)D3)-treated (0.1 micrograms/kg body-weight per d for 12 d) ewes between 77 and 140 d of gestation. Treatment resulted in a significant increase in the concentration of Ca and P in foetal tissues at all stages of gestation except at 140 d when, it is suggested, foetal mineralization may approach a maximum value. This increase in Ca and P concentration in foetal tissues was associated with an increased placental transfer of Ca, though at 111 and 120 d gestation this increase was not significant. P transfer, which was only measured at 140 d gestation, was also significantly higher in treated animals. The concentrations of Ca and P in both maternal and foetal plasma were increased significantly by the 1 alpha-(OH)D3 treatment. Whereas the concentration of Ca in the plasma of foetuses was always greater than in their dams, the concentration of plasma P in treated animals, unlike controls, was lower in foetuses than dams. This suggests that the increased placental transfer of P, unlike that of Ca, may be a passive rather than an active process.

Effects of 1 alpha-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, 1,24,25-trihydroxyvitamin D3, and 1,25,26-trihydroxyvitamin D3 on mineral metabolism and 1,25-dihydroxyvitamin D concentrations in dairy cows

Six mature, nonlactating, nonpregnant Jersey cows were treated with five 1-alpha-hydroxylated metabolites of vitamin D3 to compare relative potencies of the metabolites. Blood plasma 1,25-dihydroxyvitamin D peaked at about 1000 pg/ml 12 h after intramuscular injection of 500 micrograms 1,25-dihydroxyvitamin D3 but returned to preinjection concentration within 3 to 4 days. Administration of 500 micrograms 1-alpha-hydroxyvitamin D3 intramuscularly led to a gradual increase in 1,25-dihydroxyvitamin D concentration to 500 pg/ml 48 h after treatment. When 500 micrograms of 1,25-dihydroxyvitamin D3 or 1 alpha-hydroxyvitamin D3 were given orally, plasma 1,25-dihydroxyvitamin D peaked at about 200 and 100 pg/ml, respectively. The decline from peak concentrations occurred more slowly after oral treatment than after intramuscular treatment. Plasma calcium was increased by 20 to 30% for a week or more, depending on 1,25-dihydroxyvitamin D concentrations in plasma. All treatments resulted in calciuria. Treatment with 1 or 3 mg doses of 1,24(R),25-trihydroxyvitamin D3 or both carbon-25 stereoisomers of 1,25,26-trihydroxyvitamin D3 induced smaller and less protracted changes in plasma minerals.