Microradiographic evaluation of bone from cows with experimental hypervitaminosis D, diet-induced hypocalcemia, and naturally occurring parturient paresis

Osteoporosis is the cause of spontaneous humeral fracture in dairy cows from New Zealand

Outbreaks of humeral fractures in dairy cows have been reported in New Zealand for several years. Gross, histologic, and histomorphometric findings in the humerus from primiparous cows with spontaneous humeral fracture were compared to age-matched control cows. Affected cows had a complete nonarticular spiral fracture of the humerus. Histologically affected humeri had a thicker growth plate with abnormal architecture, thinner cortex with increased abnormal resorption, increased resorption in the distal humerus, decreased trabecular density, abnormal trabecular architecture, presence of growth arrest lines and woven bone formation. Histomorphometry showed reduction in bone volume, trabecular perimeter, and trabecular width. Cows grazed on fodder beet had thicker growth plates with an abnormal appearance compared with cows grazed on pasture, and cows with low/marginal liver copper concentration had more resorption cavities in the distal humerus and thinner cortical bone compared with cows with adequate liver copper concentration. Decreased trabecular density (OR = 249.5), abnormal cortical resorption (OR = 54.2), presence of woven bone formation in the proximal metaphysis (OR = 37.2), and the number of resorption cavities in the distal humerus were significantly associated with a high probability of fracture. Ribs had enlargement of the costochondral junction with fractures in different stages of healing. Histology of the ribs revealed abnormal growth plate appearance, presence of fracture lines, callus tissue, fibrosis, and microfractures. Cows with humeral fracture have osteoporosis due to decreased bone formation and increased bone resorption, likely associated with inadequate feed quality and perhaps copper deficiency leading to a reduction in bone strength and fracture.

Calcium and phosphorus metabolism in peripartal dogs

Recommended allowances for calcium and phosphorus are mostly based on factorial calculations partly set at the level determined adequate for giant breeds (Nutrient requirements of dogs and cats. Washington, DC, USA: The National Academies Press. 2006). Information about appropriateness of supply with both minerals during the peripartal phase is limited. From other species is known that bone mineral stores are used in addition to oral intake of calcium and phosphorus in periods of higher needs such as gestation and lactation. The aim of this study was to determine parameters of calcium and phosphorus homeostasis in female dogs receiving the recommended amount of these minerals according to NRC (Nutrient requirements of dogs and cats. Washington, DC, USA: The National Academies Press. 2006) during the peripartal phase. In five Beagles and four Foxhound crossbreds, all primiparous with a litter size of 1-8 puppies, apparent digestibility of calcium and phosphorus as well as serum parameters of mineral metabolism (total and ionised calcium, phosphorus, parathyroid hormone, bone specific alkaline phosphatase, crosslaps) was determined in the period of 12-9 days before and 4-9 days after parturition. The apparent digestibility of calcium was relatively low and did not differ significantly between both peripartal phases, whereas the apparent digestibility of phosphorus increased during lactation. Serum concentrations of calcium (total as well as ionised), phosphorus and parathyroid hormone did not differ between gestation and lactation. The bone resorption marker serum crosslaps increased in lactating dogs but most individual values were within the reference range for adult female dogs at maintenance. On the other hand, the bone formation marker bone specific alkaline phosphatase decreased from prepartal to postpartal phase with values clearly above reference range in both phases. Based on the results especially of the bone markers, which stayed within the reference range during the peripartal phase without indicating predominant bone resorption, we hypothesise that the applied recommended daily allowances defined for peripartal dogs are appropriate.

Physiological skeletal gains and losses in rat mothers during pregnancy and lactation are not observed following uteroplacental insufficiency

Fluctuations in maternal bone mass during pregnancy and lactation facilitate calcium transfer to offspring. Uteroplacental insufficiency causes fetal growth restriction and programs poor adult bone health. We aimed to characterise maternal skeletal phenotype during normal pregnancy and pregnancy complicated by uteroplacental insufficiency. Uteroplacental restriction (Restricted) or sham surgery (Control) was performed on gestational Day 18 (term=22 days) in pregnant Wistar-Kyoto rats. Maternal right femurs were collected on embryonic Day 20, postnatal Day 1 and Weeks 5, 7 and 9 postnatal. Dual-energy X-ray absorptiometry was used to quantify global bone mineral content, density and body composition. Peripheral quantitative computed tomography was utilised to determine trabecular and cortical content, density, circumferences and strength. Control rats exhibited expected reductions in trabecular and cortical content, density and bone strength from embryonic Day 20 to postnatal Day 1 (P<0.05). These skeletal alterations were absent in Restricted rats. By postnatal Day 7, bone parameters in Control and Restricted rats were not different from non-pregnant rats, indicating restoration of maternal bone. The lack of bone loss in mothers suffering uteroplacental insufficiency suggests that calcium transfer to pups would be impaired. This reduction in calcium availability is a likely contributor to the programming of poor adult bone health in growth-restricted offspring.

Adapting to the transition between gestation and lactation: differences between rat, human and dairy cow

Adequate blood calcium concentrations are vital for the normal function of mammals. Mechanisms for maintaining normal blood calcium function adequately most of the time; however, occasionally they fail and calcium homeostasis is compromised. Milk fever or periparturient hypocalcemia in dairy cattle is a well-documented example of a breakdown in the mechanisms of calcium homeostasis. This disease occurs at the time of parturition and is unique to adult dairy animals. The disease results from the inability of animals to cope with the sudden demand for calcium in support of colostrum formation. Animals developing the disease become hypocalcemic and require intravenous calcium to survive. The precise metabolic disorder(s) responsible for the onset of milk fever is still being debated. This report will highlight some of the current concepts related to the causes and prevention of milk fever in dairy cattle, as well as contrasting differences in calcium demands that exist between dairy cattle, humans and rats at the onset of lactation.

Calcium and vitamin D metabolism during lactation

Calcium transfer to the fetus in late pregnancy and the subsequent transfer of calcium to milk represent the greatest challenges to calcium homeostasis in adult animals. The adaptation of the maternal calcium homeostatic mechanisms is the result of a complex interplay between calciotropic hormones and the tissues, intestine, bone, and kidney, responsible for providing the large amounts of calcium needed to support fetal skeletal growth and lactation. In this review, we will discuss general calcium homeostasis followed by a review of the specific adaptations required by the human, rat, and cow to meet fetal and lactational demands for calcium. Finally, we will review what is known about the regulation of calcium transfer from the plasma to the milk.

Biochemical indicators of bone metabolic activity in bovine periparturient hypocalcemia

Twenty-one paretic and 30 nonparetic periparturient ambulatory cows were studied together with 13 non-pregnant control cows. Blood samples were collected during a time period of 6 hours before or after parturition and from nonpregnant cows. A severe hypocalcemia (-44%) and hypophosphatemia (-69%) were found in the paretic vs. nonparetic periparturient animals, whereas serum magnesium concentrations were not altered. Serum alkaline phosphatase activity was modestly (-12%) but not significantly decreased in the paretic vs. nonparetic periparturient cows. Serum osteocalcin concentrations, which reflect osteoblast activity, were strikingly low during the periparturient period and more in the paretic cows but the difference between the paretic (-36%) and nonparetic animals was not statistically significant. In the paretic cows, serum 1,25-dihydroxyvitamin D concentrations were significantly increased (+53%) and those of hydroxyproline decreased (-18%) compared with the nonparetic animals. Serum estradiol levels were markedly increased in the periparturient vs. nonpregnant cows and more in the paretic animals, but, again, the difference between the paretic (+47%) and nonparetic animals was not statistically significant. Serum retinol concentrations were significantly lower (-18%) in the paretic vs. nonparetic periparturient cows probably reflecting increased lactation in the paretic animals. Collectively, the results indicate very low bone metabolic activity in the periparturient vs. nonpregnant cows and support the hypothesis of both osteoblast and osteoclast functions being impaired in the paretic animals.

Plasma osteocalcin concentrations in cattle under various pathophysiological conditions

Plasma osteocalcin (BGP) concentrations were measured using an homologous radioimmunoassay in plasma samples (n = 6-14 per group) from fetal and newborn calves, 16-month-old heifers and bulls, and pregnant lactating cows. The highest values (nM) (62 +/- 3) were measured in fetal calves and the lowest (15 +/- 3) in 9-year-old pregnant and lactating cows. No significant relationship could be demonstrated between plasma BGP and somatomedin C, or 1,25(OH)2D or calcium concentrations. In eight normally calving cows, parturition was followed by a progressive increase in plasma BGP concentration, maximum 3 days after calving. It returned to prepartum values 10 days later. In six parturient hypocalcaemic and paretic cows, hypocalcaemia occurring within 12 h following calving was associated with a prompt and very transient increase in plasma BGP concentrations. These results indicate that osteocalcin might play a role in the regulation of bone metabolism in cattle.

Study of osteogenesis in adult sheep on a high and a low calcium ration by means of fluorescing bone markers

The rate of osteogenesis was studied in 8 non-pregnant, non-lactating Friesian dairy sheep, 3-6 years old, by means of a treatment with 3 different bone seeking agents. Four sheep were fed a low calcium ration (LCa:1.8 g Ca/d) and four other sheep a high calcium ration (HCa:12.7 g Ca/d). The bone markers, oxytetracycline-HCl, alizarine-complexion and demeclocycline-HCl, were administered at intervals of 6 weeks, and the sheep were killed 1 week after administration of the last marker. In undecalcified cross sections from the middle of ribs 2, 10 and 12, and from the proximal and distal parts of rib 10, the numbers of labelled osteons and the number of osteons with 1, 2 or 3 markers were counted under fluorescent microscopy. In the ribs of sheep from the LCa group, the number of labelled osteons and the quantity of labels per osteon tended to be higher than those of sheep from the HCa group. When osteogenic activity was compared in the different sites of ribs analysed, lowest osteogenic activity was observed in the proximal part of the 10th rib. The use of fluorescing markers offers the possibility of studying osteogenic activity over a certain period of time in adult sheep.

Regulation of calcium and phosphorus homeostasis in the dairy cow

This paper describes the mechanism of calcium and phosphorus homeostasis in dairy cows in an effort to provide a clearer understanding of the rationale behind current management and supplementation practices. Specifically addressed is the need to keep prepartum dietary calcium intake at less than or equal to 50 g/d to minimize the incidence of milk fever. Also discussed is the need to increase National Research Council recommendations for postpartum dietary calcium from 2.7 to 3.4 g/kg milk. This is particularly important during the first 1 to 2 mo of lactation to maintain calcium balance.

Regulation of bone mineral loss during lactation

The effects of varying dietary calcium and phosphorus content, vitamin D deficiency, oophorectomy, adrenalectomy, and simultaneous pregnancy on bone mineral loss during lactation were examined in rats. Unless otherwise stated, the diet contained 0.47% calcium and 0.3% phosphorus and the rats were given 26 nmol of vitamin D3. Femur ash weights were determined after 21 days of lactation and on age-matched nonlactating rats. Decreasing dietary calcium to 0.02% caused an increased loss of bone mineral, whereas increasing dietary calcium to 1.4% increased plasma calcium levels to 12 mg/100 ml but did not diminish the bone mineral loss observed during lactation. Varying dietary phosphorus did not have a major effect on bone mineral loss during lactation. In vitamin D-deficient rats, bone mineral loss during lactation was independent of dietary calcium levels and slightly greater than the loss observed in vitamin D-replete rats fed the normal calcium diet. Oophorectomy and adrenalectomy did not produce changes in femur ash weights of nonlactating rats or reduce bone mineral loss during lactation. Rats mated during their postpartum estrus and thus simultaneously pregnant and lactating, lost the same amount of bone mineral as caused by lactation alone.

Effects of a low calcium diet on feed intake, milk production, and response to blood calcium challenge in lactating Holstein cows

Twenty-four lactating cows were fed a normal-calcium (.75% of dry matter) diet plus free-choice dicalcium phosphate supplement for 8 wk, a low-calcium (.25% of dry matter) diet for 9 wk, and a low-calcium (.25% of dry matter) diet plus free-choice supplement for 4 wk. The low-calcium diet did not appear to affect adversely feed intake, milk production, or plasma ions. Depression of plasma calcium by sequestration with a chelating agent was less following low intake of calcium than following adequate calcium intake. Presumably, lower calcium intake increased parathyroid hormone which resulted in a larger and more responsive calcium pool immediately mobilizable. Changes in plasma phosphorus and magnesium were similar among treatments. Low calcium intake for short times apparently will not affect intake or production and may increase resistance to calcium stress such as hypocalcemia and parturient paresis.