Calcium Homeostasis and Bone Metabolism in Goats Fed a Low Protein Diet

The objective of this study was to investigate the effects of low-protein diets on blood calcium (Ca) level, bone metabolism, and the correlation between bone metabolism and blood calcium in goats. Twenty-four female Xiangdong black goats with similar body weight (19.55 ± 3.55 kg) and age (8.0 ± 0.3 months) were selected and allocated into two groups: control group (CON, 10.77% protein content) and low-protein group (LP, 5.52% protein content). Blood samples were collected on days 1, 4, 7, 16 and 36 before morning feeding to determine the concentration of calcium (Ca), parathyroid hormone (PTH), bone gla protein (BGP), C-terminal telopeptide of type 1 collagen (CTX-1), bone alkaline phosphatase (BALP), and 1, 25-dihydroxyvitamin D3 [1,25(OH)₂D3]. Liver samples were collected to determine the expression of bone metabolism-related genes. There was no difference observed between LP and CON in concentration of plasma Ca or any of bone metabolism markers (P > 0.05). In the liver, the mRNA expression of bone gamma carboxyglutamate protein (BGLAP), alkaline phosphatase (ALPL), and mothers against decapentaplegic homolog-1 (SMAD1) were increased (P < 0.05) in LP as compared with CON. The correlation analysis of Ca and bone metabolism markers showed no significant correlation between Ca and bone metabolism. These results suggest that the blood Ca concentration in mature goats may keep at a stable level through nitrogen cycling when the providing protein is not enough.

Effects of diets differing in dietary cation-anion difference and calcium concentration on calcium homeostasis in neutered male sheep

Feeding low dietary cation-anion difference (DCAD) diets is one strategy to prevent milk fever in cows. The mechanism of action, as well as whether the calcium (Ca) supply of such diets combined with this feeding regimen should meet the requirements, is still unclear. Small ruminants are commonly used as models for cows. The goal of the present study was to demonstrate basic effects of DCAD against a background of different Ca supplies in a sheep model. Twenty-three castrated male East Friesian milk sheep, aged 11 to 12 mo, were randomly assigned to 4 different feeding groups. The ration of each group was either high (highDCAD) or low in DCAD (lowDCAD) combined with adequate (nCa) or restricted Ca supply (lowCa). At baseline, serum and urine were collected from all sheep and a peripheral quantitative computed tomography of the left metatarsus was performed. After a 14-d adaptation period to the different diets, the experiment started (d 0). Urine, feces, and serum were collected on d 0, 4, 7, 14, and 22, and peripheral quantitative computed tomography was performed on d 0 and 22. On d 22, the sheep were killed and sampled for functional studies. LowDCAD was significantly associated with lower urine pH, higher urinary Ca excretion, higher ionized Ca in blood, and higher serum Ca concentrations. Blood pH and bone parameters did not differ significantly between groups. It is unclear from which compartment the high amounts of Ca excreted with urine in the lowDCAD groups originated. Interestingly, lowDCAD resulted in higher renal mRNA abundance of parathyroid hormone receptor but unaffected mRNA abundance of Ca transporters. As neither renal abundance of these transporters nor Ca excretion were influenced by dietary Ca supply, our results support the hypothesis that increased urinary Ca observed with low DCAD diets represents a loss rather than an excretion of surplus Ca.

Boron supplementation in peripartum Murrah buffaloes: The effect on calcium homeostasis, bone metabolism, endocrine and antioxidant status

BACKGROUND

Calcium homeostasis and immuno-endocrine system undergoes drastic changes in peripartum dairy animals and failure to adapt these physiological changes causes major impact on animal health as well as productivity. Boron (B), a newer trace element, influences calcium (Ca), phosphorus (P) and magnesium (Mg) metabolism as well as immune system by manipulating several hormones or enzyme systems. Present study was conducted to determine the effect of dietary B supplementation on Ca homeostasis, bone metabolism, endocrine and antioxidant status in peripartum Murrah buffaloes.

METHODS

Thirty advanced pregnant Murrah buffaloes (8th month pregnant) were allocated into three groups based on their most probable producing ability (MPPA) and parity (n = 10 in each group) viz. B0, B200 and B400 and supplemented with 0, 200 and 400 ppm of B in the form of boric acid. Blood samples were collected at periodic intervals (-45, -30, -21, -15, -7, 0, 7, 15, 30, 60, 90 and 120 day relative to expected date of calving) and analysed for minerals concentration, hormonal profile, bone health biomarkers and antioxidant enzymes.

RESULTS AND CONCLUSION

Boron supplementation at 200 and 400 ppm increased (p < 0.05) plasma Ca, Mg and osteocalcin (OCN) concentration during postpartum stage. Higher (p < 0.05) levels of plasma 25-hydroxy vitamin D₃ were observed in both B supplemented groups as compared to B unsupplemented group irrespective of physiological stages. Plasma parathyroid hormone (PTH) and cortisol levels were lower (p < 0.05) in both B supplemented groups than B unsupplemented group, especially during postpartum stage. Whereas, plasma ferric reducing total antioxidant power (FRAP) activity was found to be higher (p < 0.05) in B supplemented groups as compared to B unsupplemented group. Furthermore, antioxidant enzymes (erythrocytic superoxide dismutase; SOD, catalase, glutathione peroxidase; GPx), plasma level of total immunoglobulins (TIg), bone specific alkaline phosphatase (BALP) and tartrate resistant acid phosphatase (TRAP) remained unaffected by dietary B supplementation. Overall, it can be concluded that supplementation of B at 200 ppm in the diet of peripartum Murrah buffaloes helped to induce metabolic adaptations for improving Ca homeostasis, bone metabolism and antioxidant status without much additional benefits at higher level used in the present study.

Review: Regulation of gastrointestinal and renal transport of calcium and phosphorus in ruminants

In comparison to monogastric animals, ruminants show some peculiarities in respect to the regulation of mineral homeostasis, which can be regarded as a concerted interplay between gastrointestinal absorption, renal excretion and bone mobilisation to maintain physiological Ca and phosphate (Pi) concentrations in serum. Intestinal absorption of Ca or Pi is mediated by two general mechanisms: paracellular, passive transport dominates when luminal Ca or Pi concentrations are high and transcellular. The contribution of active transport becomes more important when dietary Ca or Pi supply is restricted or the demand increased. Both pathways are modulated directly by dietary interventions, influenced by age and regulated by endocrine factors such as 1,25-dihydroxyvitamin D3. Similar transport processes are observed in the kidney. After filtration, Ca and Pi are resorbed along the nephron. However, as urinary Ca and Pi excretion is very low in ruminants, the regulation of these renal pathways differs from that described for monogastric species, too. Furthermore, salivary secretion, as part of endogenous Pi recycling, and bone mobilisation participate in the maintenance of Ca and Pi homeostasis in ruminants. Saliva contains large amounts of Pi for buffering rumen pH and to ensure optimal conditions for the rumen microbiome. The skeleton is a major reservoir of Ca and Pi to compensate for discrepancies between demand and uptake. But alterations of the regulation of mineral homeostasis induced by other dietary factors such as a low protein diet were observed in growing ruminants. In addition, metabolic changes, for example, at the onset of lactation have pronounced effects on gastrointestinal mineral transport processes in some ruminant species. As disturbances of mineral homeostasis do not only increase the risk of the animals to develop other diseases, but are also associated with protein and energy metabolism, further research is needed to improve our knowledge of its complex regulation.

Effect of calcium intake and the dietary cation-anion difference during early lactation on the bone mobilization dynamics throughout lactation in dairy cows

This study investigated the consequences of a low supply of dietary Ca with or without a low dietary cation-anion difference (DCAD) during early lactation on bone mobilization and reconstitution during lactation and on the dynamics of milk Ca content. Fifteen multiparous Holstein cows were distributed among 3 treatments 5 weeks before their expected calving date. These treatments differed based on the provision of diets through the first 10 weeks of lactation. During this period, the control treatment (NCa) consisted of a diet providing 100% of the Ca requirement, with a DCAD of 200 mEq/kg dry matter (DM). The LCa (low Ca) and LCaLD (low Ca, low DCAD) treatments consisted of diets providing 70% of the Ca requirement, with a DCAD of 200 and 0 mEq/kg DM, respectively. After 10 weeks, all cows received the same total mixed ration, which was formulated to meet 100% of the Ca requirement. LCa and LCaLD tended to decrease the body retention of Ca at 3 weeks of lactation compared with NCa but affected neither the dynamics of the blood biomarkers of bone formation and resorption during lactation nor the body retention of Ca at 17 weeks of lactation. Cows almost entirely compensated for the decrease in Ca supply caused by LCa and LCaLD by increasing their apparent digestive absorption of Ca at 3 weeks of lactation, whereas their apparent digestive absorption was unaffected by the treatments at 17 weeks of lactation. Milk production tended to be lower throughout lactation with LCa and LCaLD compared with NCa, with a mean difference of 2 kg/d. The results of this study also indicated that measuring the dynamics of milk Ca content during lactation cannot be considered effective for indirectly estimating the dynamics of bone mobilization in cows. The results also suggested that limited Ca intake at the beginning of lactation may have deleterious effects on milk production.

Effect of parity number on the dry matter intake of dairy cows during the first week after calving

We investigated the effect of parity number on the dry matter intake (DMI) of cows during the first week after calving. Eighty-three cows were evaluated from 14 days before to 7 days after calving. DMI and milk yield were measured for 7 days after calving, and the calving score was measured. Blood samples were collected throughout the experiment. The average DMI during the first week after calving was reduced in the first-lactation heifers and high-parity number cows. A quadratic relationship between the parity number and the DMI was observed. The first-lactation heifers had lower prepartum serum total protein (TP) concentration and milk yield, higher prepartum serum nonesterified fatty acid (NEFA) concentration and calving score than the multiparous cows. The recovery rate of serum calcium (Ca) after calving was slow in the cows in the parity 6. The DMI was positively affected by the serum Ca concentration after calving, milk yield, and prepartum serum TP concentration and was negatively affected by the calving score and prepartum serum NEFA concentration. We conclude that the DMI immediately after calving tends to be lower in first-lactation heifers and high-parity number cows, but factors that reduce the DMI differ according to parity number.

Serum calcium dynamics within the first 3 days in milk and the associated risk of acute puerperal metritis

The objectives of this study were to evaluate postpartum serum calcium dynamics for different parity groups of dairy cows and to assess whether serum calcium concentration on d 0, 1, and 3 postpartum was associated with the risk of developing acute puerperal metritis (APM). The study took place on a commercial dairy farm in northern Germany and included 4,043 Holstein dairy cows. Calving difficulties, such as dystocia, twins, or stillbirth, were recorded. Blood samples were obtained on d 0, 1, and 3 after calving for analysis of serum calcium concentration. Animals were examined daily for clinical symptoms of retained placenta, APM, mastitis, and displaced abomasum until 10 d in milk. To determine serum calcium dynamics postpartum, we performed repeated-measures ANOVA with first-order autoregressive covariance. A logistic regression model was used to evaluate the association of serum calcium concentration with the risk of developing metritis. Serum calcium concentration was affected by time relative to calving, parity, and APM. Increasing parity negatively affected serum calcium concentration on d 0 and 1. Serum calcium concentration reached its lowest level on d 1 and 3 in multiparous and primiparous cows, respectively. The concentration increased from d 1 to 3 in multiparous cows and decreased from d 0 to 3 in primiparous cows. The association of APM and serum calcium dynamics varied by parity. On d 3, serum calcium concentration was significantly lower in animals with subsequent APM than in those without APM. The overall incidence of APM was 12.0% (primiparous cows, 20.4%; multiparous cows, 8.6%). An association existed between serum calcium concentration on d 3 after calving and APM. Primiparous cows had an odds ratio of 0.12 for serum calcium concentration on d 3, indicating that a primiparous cow with serum calcium concentration of 2.5 mmol/L had a 88% lower chance of developing APM compared with a cow with a concentration of 1.5 mmol/L. Multiparous cows had an odds ratio of 0.34 for serum calcium concentration on d 3, indicating that a multiparous cow with serum calcium concentration of 2.5 mmol/L had a 66% lower chance of developing APM compared with a cow with a concentration of 1.5 mmol/L. Primiparous cows with low serum calcium concentration had the highest predicted probability of developing APM. Our results reveal a dynamic in serum calcium concentration in the first 3 d in milk. Consequently, the day of sampling and the observed risk period for hypocalcemia are important when conducting epidemiological studies to evaluate associations between hypocalcemia and clinical diseases.

Is bone loss a physiological cost of reproduction in the Great fruit-eating bat Artibeus lituratus?

During mammalian pregnancy and lactation, the maternal demand for calcium is increased to satisfy fetus and newborn skeletal growth. In addition to the dietary intake, females use the calcium contained in their bones to supply this increased demand, leading to a decrease in maternal bone mineral content. In reproductive insectivorous female bats, bone loss has been described as a physiological cost of reproduction, due to the reported increased risk of bone fracture. This physiological cost may be the mechanism underlying the conflict between increasing litter size and maintaining wing skeletal integrity, which would help to explain the small litter size of most bat species. If bone loss is a linking cost between reproduction and survival in bats, and most bat species have small litter sizes, one would expect to find a loss of bone and an increasing probability of bone fracture during pregnancy and lactation in other non-insectivorous bats. In this study, we tested for the existence of this cost in the Great-fruit eating bat, Artibeus lituratus. We analyzed trabecular structure, bone strength and bone mineral content for the humerus bone, hypothesizing that bone loss during reproduction in females would increase the risk of fracture. Our results showed a decrease of 22-31% in bone trabecular area in lactating females, rapidly compensated following weaning. Bone strength did not differ among reproductive and non-reproductive groups and seems to be more influenced by bone organic components rather than mineral contents. Since we observed bone loss during reproduction yet the humerus strength seems to be unaffected, we suggest that bone loss may not represent a physiological cost during reproduction for this frugivorous bat.

Development of mathematical models to predict calcium, magnesium and selenium excretion from lactating Holstein cows

The aim of this study was to develop and evaluate mathematical models that predict mineral excretion, particularly calcium (Ca), magnesium (Mg) and selenium (Se), from lactating dairy cows. Mineral excretion can be affected by several dietary factors. A deficiency in Ca or Mg application to pasture, among other factors, can contribute to grass tetany or wheat pasture poisoning in cows, whereas an excess can cause runoff into water supplies. Manure application with high Se concentration can also result in runoff, causing the bioaccumulation of selenium in aquatic ecosystems, wetland habitats and estuaries, leading to toxic levels in fish. A database composed of studies relating to mineral utilisation in lactating dairy cows conducted after and including the year 2000 was compiled. A meta-analysis was conducted with the aim of creating multiple empirical equations to predict Ca, Mg and Se excretion from lactating dairy cows. Calcium intake, feed Ca content, milk yield, milk protein content and acid detergent fibre content in diet were positively and linearly related to Ca excretion. Dietary crude protein content and milk fat content were negatively related to Ca excretion. Magnesium intake, feed Mg content and milk yield were positively and linearly related to Mg excretion. Selenium content of diet and dry matter intake were linearly and positively related to Se excretion. Two sets of models were developed using or excluding the intake variable and both sets of models were evaluated with independent data originating from commercial herd or individual animals. In general, intake measurements improved prediction when evaluated with independent datasets (root mean square prediction error = 8% to 19% vs 14% to 26% of the average observed value). There were substantial mean biases, particularly those evaluated with data from a commercial farm, perhaps due to inaccurate feed intake measurements. Although there was generally good agreement between predicted and observed mineral excretion, model development and evaluation would benefit from an expanded database.

Nutritional strategies in ruminants: A lifetime approach

This review examines the role of nutritional strategies to improve lifetime performance in ruminants. Strategies to increase ruminants' productive longevity by means of nutritional interventions provide the opportunity not only to increase their lifetime performances and their welfare, but also to decrease their environmental impact. This paper will also address how such nutritional interventions can increase herd efficiency and farm profitability. The key competencies reviewed in this article are redox balance, skeletal development and health, nutrient utilization and sustainability, which includes rearing ruminants without antibiotics and methane mitigation. While the relationships between these areas are extremely complex, a multidisciplinary approach is needed to develop nutritional strategies that would allow ruminants to become more resilient to the environmental and physiological challenges that they will have to endure during their productive career. As the demand of ruminant products from the rapidly growing human world population is ever-increasing, the aim of this review is to present animal and veterinary scientists as well as nutritionists a multidisciplinary approach towards a sustainable ruminant production, while improving their nutrient utilization, health and welfare, and mitigation of their carbon footprint at the same time.

Bone turnover markers in sheep and goat: A review of the scientific literature

Bone turnover markers (BTMs) are product of bone cell activity and are generally divided in bone formation and bone resorption markers. The purpose of this review was to structure the available information on the use of BTMs in studies on small ruminants, especially for monitoring their variations related to diet, exercise, gestation and metabolic lactation state, circadian and seasonal variations, and also during skeletal growth. Pre-clinical and translational studies using BTMs with sheep and goats as animal models in orthopaedic research studies to help in the evaluation of the fracture healing process and osteoporosis research are also described in this review. The available information from the reviewed studies was systematically organized in order to highlight the most promising BTMs in small ruminant research, as well as provide a wide view of the use of sheep and goat as animal models in orthopaedic research, type of markers and commercial assay kits with cross-reactivity in sheep and goat, method of sample and storage of serum and urine for bone turnover markers determination and the usefulness and limitations of bone turnover markers in the different studies, therefore an effective tool for researchers that seek answers to different questions while using BTMs in small ruminants.

Utilising mobilisation of body reserves to improve the management of phosphorus nutrition of breeder cows

Phosphorus (P) deficiency is a major constraint to the productivity of breeder herds grazing low-P rangelands due to adverse effects on growth and fertility. However, P supplementation during the wet season, when additional dietary P is most needed, is often difficult due to practical constraints. Body P reserves in breeders can be mobilised and alleviate dietary P deficiency within an annual cycle. Approaches to estimate bone P reserves and net mobilisation or replenishment of P from the analysis of rib and hip (tuber coxae) biopsies are discussed. In at least some circumstances, breeder cows grazing P-deficient pastures mobilise bone P to alleviate the effects of diet P deficiency. Recent experiments with breeders have investigated mobilisation of body P to alleviate the adverse effects of dietary P deficiency during pregnancy and early lactation, and subsequent replenishment of body P reserves. Both mature cows and first-calf cows (FCC) calving in a high P status and fed severely P-deficient diets during lactation were able to mobilise sufficient body P reserves to provide milk for moderate calf growth (viz. 0.6–0.8 kg liveweight (LW)/day for 3 months), but this was associated with rapid cow-LW loss and markedly decreased bone P content. First-calf cows appear to have lesser capacity than mature cows to mobilise body P. FCC fed P-adequate diets during late pregnancy maintained high voluntary intakes and had higher LW and bone P reserves at calving. When fed a P-deficient diet during early lactation, these greater bone P reserves were utilised. Bone P reserves can be replenished by P-adequate diets fed post-weaning. Breeder management that relies more on mobilising body P reserves when P demands are high and on replacing these body P reserves when P demands are lower offers an opportunity to alleviate the effects of dietary P deficiencies during the early wet season in situations where P supplementation is not possible.

Renal mechanisms of calcium homeostasis in sheep and goats

In small ruminants, the renal excretion of calcium (Ca) and phosphate (Pi) is not modulated in response to dietary Ca restriction. Although this lack of adaptation was observed in both sheep and goats, differences in renal function between these species cannot be excluded. Recent studies demonstrated that compared with sheep, goats have a greater ability to compensate for challenges to Ca homeostasis, probably due to a more pronounced increase in calcitriol production. Therefore, the aim of the present study was to examine the effect of 1) dietary Ca restriction, 2) administration of calcitriol, and 3) lactation on Ca and Pi transport mechanisms and receptors as well as enzymes involved in vitamin D metabolism in renal tissues of sheep and goats. Whereas RNA expression of renal transient receptor potential vanilloid channel type 5 was unaffected by changes in dietary Ca content, a significant stimulation was observed with administration of calcitriol in both sheep (P < 0.001) and goats (P < 0.01). Calbindin-D28K was downregulated during dietary Ca restriction in goats (P < 0.05). Expression of the sodium/Ca exchanger type 1 was decreased by low Ca intake in sheep (P < 0.05) and upregulated by calcitriol treatment in goats (P < 0.05). A significant reduction in RNA expression of the cytosolic and the basolateral Ca transporting proteins was also demonstrated for lactating goats in comparison to dried-off animals. Species differences were found for vitamin D receptor expression, which was stimulated by calcitriol treatment in sheep (P < 0.01) but not in goats. As expected, expression of 1α-hydroxylase was upregulated by dietary Ca restriction (P < 0.001; P < 0.05) and inhibited by exogenous calcitriol (P < 001; P < 0.05) in both sheep and goats. However, whereas 24-hydroxylase expression was stimulated to the same extent by calcitriol treatment in sheep, irrespective of the diet (P < 0.001), a modulatory effect of dietary Ca supply on 24-hydroxylase induction was observed in goats (P < 0.05). Taken together, our results confirm observations that modulation of renal Ca excretion does not contribute to maintenance of Ca homeostasis in these ruminants during restricted dietary supply, unlike responses in monogastric animals. The interesting species differences related to vitamin D metabolism might explain the greater capacity of goats to compensate for challenges of Ca homeostasis and should be further investigated.

Prediction of phosphorus output in manure and milk by lactating dairy cows

Mathematical models for predicting P excretions play a key role in evaluating P use efficiency and monitoring the environmental impact of dairy cows. However, the majority of extant models require feed intake as predictor variable, which is not routinely available at farm level. The objectives of the study were to (1) explore factors explaining heterogeneity in P output; (2) develop a set of empirical models for predicting P output in feces (Pf), manure (PMa), and milk (Pm, all in g/cow per day) with and without dry matter intake (DMI) using literature data; and (3) evaluate new and extant P models using an independent data set. Random effect meta-regression analyses were conducted using 190 Pf, 97 PMa, and 118 Pm or milk P concentration (PMilkC) treatment means from 38 studies. Dietary nutrient composition, milk yield and composition, and days in milk were used as potential covariates to the models with and without DMI. Dietary phosphorus intake (Pi) was the major determinant of Pf and PMa. Milk yield negatively affected Pi partitioning to Pf or PMa. In the absence of DMI, milk yield, body weight, and dietary P content became the major determinants of Pf and PMa. Milk P concentration (PMilkC) was heterogeneous across the treatment groups, with a mean of 0.92 g/kg of milk. Milk yield, days in milk, and dietary Ca-to-ash ratio were negatively correlated with PMilkC and explained 42% of the heterogeneity. The new models predicted Pf and PMa with root mean square prediction error as a percentage of observed mean (RMSPE%) of 18.3 and 19.2%, respectively, using DMI when evaluated with an independent data set. Some of the extant models also predicted Pf and PMa well (RMSPE%=19.3 to 20.0%) using DMI. The new models without DMI as a variable predicted Pf and PMa with RMSPE% of 22.3 and 19.6%, respectively, which can be used in monitoring P excretions at farm level. When evaluated with an independent data set, the new model and extant models based on milk protein content predicted PMilkC with RMSPE% of 12.7 to 19.6%. Although models using P intake information gave better predictions, P output from lactating dairy cows can also be predicted well without intake using milk yield, milk protein content, body weight, and dietary P, Ca, and total ash contents.

Supplementation with difructose anhydride III promotes passive calcium absorption in the small intestine immediately after calving in dairy cows

The incidence of hypocalcemia increases in high-parity dairy cows because resorption of bone Ca is delayed in these animals, and they appear to have a reduced ability to absorb Ca from the intestine during the early postpartum period. Difructose anhydride (DFA) III has been shown to promote the absorption of intestinal Ca via a paracellular pathway. However, past studies have not reported this effect in peripartum dairy cows. Therefore, we investigated the effect of DFA III supplementation on Ca metabolism during the peripartum period to determine whether DFA III promotes intestinal Ca absorption via this route. Seventy-four multiparous Holstein cows were separated into DFA and control groups based on their parity and body weight. The feed of the DFA group was supplemented with 40g/d of DFA III from -14 to 6d relative to calving. The control group did not receive DFA III. At calving (0h relative to calving), serum Ca declined below 9mg/dL in both groups. However, serum Ca concentrations were greater in the DFA group than in the control group at 6, 12, 24, and 48h relative to calving, and the time required for serum Ca to recover to 9mg/dL during the postpartum period was shorter in the high-parity cows in the DFA group than in those in the control group. Parathyroid hormone concentrations increased immediately after calving in both groups and were greater in the control group than in the DFA group at 12 and 24h relative to calving. Serum 1,25-dihydroxyvitamin D concentrations increased at 0 and 12h relative to calving in both groups and were higher in the control group than in the DFA group at 72h relative to calving. Serum concentrations of the bone-resorption marker cross-linked N-telopeptide of type I collagen (NTX) were not different between the groups during peripartum period, and serum NTX in all cows was lower at 0, 6, 12, 24, 48, and 72h relative to calving than at -21, 4, and 5d relative to calving. Thus, DFA treatment induced faster recovery of serum Ca, although bone resorption was restrained. In conclusion, DFA III promotes intestinal passive Ca absorption via the paracellular pathway during the early postpartum period; this absorption is unaffected by aging.

Differences in peripartal plasma parameters related to calcium homeostasis of dairy sheep and goats in comparison with cows

Recently it has been demonstrated that there are differences between sheep and goats in respect to adaptation to a calcium-restricted diet. It was the aim of the present study to evaluate whether species-specific peculiarities also occur when calcium homoeostasis is challenged by lactation. Therefore, we investigated the time courses of plasma parameters related to calcium homoeostasis (calcium, phosphate, calcitriol, the bone resorption marker CrossLaps® and the bone formation marker osteocalcin) during the transition period in multiparous animals of both species and compared the results to data from a former study carried out with dairy cows. As in cows, plasma calcium and the ratio of bone formation to bone resorption decreased at parturition in goats while plasma calcitriol increased. On day 10 post partum the bone parameters of goats reached prepartum values again, which was not the case in cows. Sheep were found to experience a challenge of calcium homoeostasis already 10 d before parturition, reflected by a very low ratio of bone formation to bone resorption, which was not accompanied by an increase in plasma calcitriol. Additionally, sheep and goats which had been in milk for 3 months were sampled, dried-off and sampled again 6 weeks later. In dried-off animals there were no detectable differences in parameters of bone metabolism. In conclusion we could show that the contribution of bone mobilisation to the compensation for the enhanced calcium demand due to lactation differs between the three ruminant species.

Effect of dietary phosphorus content on milk production and phosphorus excretion in dairy cows

Background

Phosphorus (P) supplementation is costly and can result in excess P excretion. This study investigated the effects of reducing dietary P on milk production and P excretion in dairy cows over a full lactation.

Method

Forty-five multiparous Holstein dairy cows were divided into 15 blocks according to expected calving date and previous milk yield, and assigned randomly to one of the three dietary treatments: 0.37, 0.47, and 0.57% P (DM basis); these P levels represent the NRC recommendations, Chinese recommendations, and the amount of dietary P commonly fed by Chinese dairy farmers, respectively. Average daily feed intake was calculated from monthly data on feed offered and refused. Milk yields of individual cows were recorded weekly, and milk samples were taken for analysis of protein, fat, solids-not-fat, lactose, and somatic cell count. Blood samples were collected on days −6, −3, 0, 3, 6 relative to calving, and then monthly throughout lactation, and analyzed for P and Ca concentrations. Spot samples of feces and urine were collected for 3 consecutive d during weeks 12, 24, and 36, and P concentrations were analyzed. Reproduction and health data were recorded.

Results

Dietary P did not affect dry matter intake or milk yield (P > 0.10). Milk fat content was slightly higher in cows fed 0.37% P than in cows fed 0.47% P (P = 0.05). Serum concentrations of P and Ca did not reflect dietary P content (P > 0.10). Fecal and urinary P both declined linearly (P < 0.05) as dietary P decreased from 0.57 to 0.37%. Fecal P content was 25% less when dietary P was 0.37% compared to 0.57%. Health events and reproductive performance were not associated with dietary P content (P > 0.05).

Conclusions

Lowering dietary P from 0.57 to 0.37% did not negatively affect milk production, but did significantly reduce P excretion into environment.

An evaluation of the effect of age and the peri-parturient period on bone metabolism in dairy cows as measured by serum bone-specific alkaline phosphatase activity and urinary deoxypyridinoline concentration

Various biochemical markers help to evaluate the state of bone turnover in humans and could be used during the peri-parturient period in dairy cows when calcium (Ca) metabolism changes dramatically. To investigate this, the peri-partum characteristics of serum bone-specific alkaline phosphatase (BAP) and urinary deoxypyridinoline (DPD) were investigated. Both serum BAP activity and urinary DPD concentrations were increased and demonstrated wide variability in younger animals, and these findings were consistent with other bone turnover markers. Around the time of parturition, serum Ca concentration and serum BAP activity in multiparous cows were significantly lower than in primiparous cows, but urinary DPD concentration was unchanged. The use of BAP as a bone formation marker appears to be valuable for evaluating bone remodelling status in cows, but the specificity of the test needs to be confirmed. The DPD/BAP ratio around parturition demonstrated a clear difference in bone turnover status between the two parity groups with multiparous cows demonstrating increased signs of bone resorption compared with primiparous cows, corresponding to the Ca requirement for milk production. In future studies, the applicability of the ratio of bone resorption marker to bone formation marker should be evaluated for bone turnover assessment.

A novel model to explain dietary factors affecting hypocalcaemia in dairy cattle

Most dairy cows exhibit different degrees of hypocalcaemia around calving because the gestational Ca requirements shift to the disproportionately high Ca requirements of lactation. Ca homeostasis is a robust system that effectively adapts to changes in Ca demand or supply. However, these adaptations often are not rapid enough to avoid hypocalcaemia. A delay in the reconfiguration of intestinal Ca absorption and bone resorption is probably the underlying cause of this transient hypocalcaemia. Several dietary factors that affect different aspects of Ca metabolism are known to reduce the incidence of milk fever. The present review describes the interactions between nutrition and Ca homeostasis using observations from cattle and extrapolations from other species and aims to quantitatively model the effects of the nutritional approaches that are used to induce dry cows into an early adaptation of Ca metabolism. The present model suggests that reducing dietary cation–anion difference (DCAD) increases Ca clearance from the blood by dietary induction of systemic acidosis, which results in hypercalciuria due to the loss of function of the renal Ca transient receptor potential vanilloid channel TRPV5. Alternatively, reducing the gastrointestinal availability of Ca by reducing dietary Ca or its nutritional availability will also induce the activation of Ca metabolism to compensate for basal blood Ca clearance. Our model of gastrointestinal Ca availability as well as blood Ca clearance in the transition dairy cow allowed us to conclude that the most common dietary strategies for milk fever prevention may have analogous modes of action that are based on the principle of metabolic adaptation before calving.

Assessment of Newcastle disease-specific T cell proliferation in different inbred MHC chicken lines

In this study, we have described the establishment of an antigen-specific T cell proliferation assay based on recall stimulation with Newcastle disease (ND) antigen; further, we have described the results obtained after recall stimulation of animals containing different major histocompatibility complex (MHC) haplotypes, vaccinated against ND. First optimization of the assay was performed to lower unspecific proliferation and to enhance antigen-specific T cell proliferation. These two issues were achieved using ethylene diamine tetra acetic acid as stabilizing agent in blood samples and autologous immune serum in culture medium. The optimized assay was used to screen chickens with different MHC haplotypes for their ability to perform T cell proliferation. Results showed that the antigen-specific response of CD4(+) and CD8(+) T cells from B12 chickens was generally low, whereas B13, B130 and B201 chickens were medium in CD4(+) or CD8(+) T cell responses. High responses were seen only in few animals of each haplotype and not in general. A polymorphism in the chicken CD8α gene was found in our experimental chicken lines, resulting in incapability to detect CD8α(+) T cells using antibodies from the CT8 clone. Screening chickens with alternative antibodies showed that antibodies from the 2-398 clone were able to discriminate all CD8α(+) cells from CD8α(-) cells, and consequently this antibody was used in a second vaccination experiment performed with chickens of the haplotypes B13 and B130. This experiment showed a significant difference in antigen-specific proliferation of CD4(+) T cells between the two lines, but not in CD8α(+) T cell proliferation.

An extended model of phosphorus metabolism in growing ruminants

A major objective of this study was to extend the Vitti-Dias model used to describe P metabolism in ruminants, by adding 2 new pools to the original model to represent the rumen and saliva. An experiment was carried out using 24 male sheep, initial BW of 34.5 kg, aged 8 mo, fed a basal diet supplied with increasing amounts of dicalcium phosphate to provide 0.14, 0.32, 0.49, and 0.65% P in the diet. Sheep were individually housed indoors in metabolic cages and injected with a single dose of 7.4 MBq of (32)P into a jugular vein. Feed intake and total fecal and urinary outputs were recorded and sampled daily for 1 wk, and blood samples were obtained at 5 min, and 1, 2, 4, 6, 24, 48, 72, 96, 120, 144, and 168 h after (32)P injection. Saliva and rumen fluid samples were taken on d 6, 7, and 8. Then, animals were slaughtered and samples from liver, kidney, testicle, muscle, and heart (soft tissue) and bone were collected. Specific radioactivity and inorganic P were then determined in bone, soft tissue, plasma, rumen, saliva, and feces, and used to calculate flows between pools. Increased P intake positively affected total P (r = 0.97, P < 0.01) and endogenous P excretion in feces (r = 0.85, P < 0.01), P flow from plasma to saliva (r = 0.73, P < 0.01), from saliva to rumen (r = 0.73, P < 0.01), and from lower gastrointestinal tract to plasma (r = 0.72, P < 0.01). Urinary P excretion was similar for all treatments (P = 0.35). It was, however, related to plasma P (r = 0.63, P < 0.01) and to net P flow to bone (accretion - resorption; r = -0.64, P < 0.01). Phosphorus intake affected net P flow to soft tissue (P = 0.04) but not net P flow to bone (P = 0.46). Phosphorus mobilized from bone was directed toward soft tissue, as suggested by the correlations between P flow from bone to plasma and net P flow to soft tissue (r = 0.89, P < 0.01), and P flow from plasma to soft tissue and net P flow to bone (r = -0.76, P < 0.01). The lack of effect of dietary P on net P accretion in bone suggests that P demand for bone formation was low and surplus P was partially used by soft tissue. In conclusion, the model resulted in appropriate biological description of P metabolism in sheep and added knowledge of the effects of surplus dietary P on P metabolism. Additionally, the model can be used as a tool to assess feeding strategies aiming to mitigate P excretion into the environment.

Gastrointestinal calcium absorption in sheep is mostly insensitive to an alimentary induced challenge of calcium homeostasis

For ruminants, marked differences to monogastric species have been described concerning the localisation and vitamin D sensitivity of gastrointestinal calcium absorption, particularly with respect to the forestomach compartment. Therefore, we investigated gastrointestinal calcium transport of sheep as influenced by a dietary calcium restriction and/or a supraphysiological dosage of exogenous calcitriol. Using the Ussing chamber technique, we determined calcium and mannitol flux rates to differentiate between para- and transcellular calcium transport in rumen, duodenum, jejunum and colon. Expression of epithelial calcium channels, calbindin-D(9K), and basolateral extrusion mechanisms was determined by quantitative RT-PCR and Western blot analysis. Active calcium transport could be demonstrated in jejunum and rumen. A significant stimulation of jejunal calcium absorption was only observed in animals treated with calcitriol. The alimentary calcium restriction alone did not result in significant effects indicating a less effective intestinal adaptation to alimentary calcium restriction than observed in monogastric animals. The observed ruminal calcium transport was not affected at all, neither by the diet nor the calcitriol treatment. Furthermore, no significant expression of epithelial calcium channels or calbindin-D(9K) could be detected in the rumen; therefore it is concluded that calcium transport in the forestomachs is probably mediated by a different, so far unknown mechanism.

Effects of 1,25-dihydroxyvitamin D3 on calcium and phosphorus homeostasis in sheep fed diets either adequate or restricted in calcium content

It was the aim of the present study to collect basic data on calcium (Ca) and phosphorus (P) homoeostasis in sheep. Two series of experiments were carried out to investigate the effects of 1,25-dihydroxyvitammin D(3) (calcitriol) in supraphysiological dosage in combination with varying alimentary Ca supply. In the first series, blood samples were collected over 72 h to determine the concentrations of total Ca (Ca), ionized Ca (Ca(2+)), inorganic phosphate (P(i)), and the bone resorption marker CrossLaps (CL). In the second series, measurements were carried out over 12h. In addition, urine samples were collected to calculate the fractional excretions (FE) of Ca and P(i). Changes in plasma macromineral concentrations (P<0.01) as well as in CL (P<0.001) and endogenous calcitriol (P<0.05) were observed in the alimentary Ca-restricted animals, indicating that the reduction of daily Ca intake challenged the animals' macromineral homeostatic mechanisms. However, the Ca-restricted diet had an effect on neither FE of Ca nor on FE of P(i). The treatment resulted in peak serum calcitriol concentrations between 1,900 and 2,500 pg/mL, and supraphysiological concentrations were maintained for the next 48 h. Irrespective of dietary Ca, calcitriol had hypercalcemic and hyperphosphatemic effects. An increase in CL was revealed only in the Ca-restricted, calcitriol-treated sheep (P<0.01), reflecting a remarkable enhancement of Ca mobilization from the bone by calcitriol exclusively in this group. From these data, it can be concluded that the sheep can be a suitable animal model for studying catabolic effects of Ca deficiency and calcitriol on bone metabolism.

Influence of calcium and phosphorus feeding on markers of bone metabolism in transition cows

A study was carried out to verify the effect of Ca and P levels on production, digestibility, and serum bone metabolism biomarkers in dairy cows. Fifty-two nonlactating multiparous cows (>or=3 lactations) were confined in a free-stall barn approximately 20 d before calving. A standard close-up diet was fed to cows once daily until d 2 postpartum. Cows were randomly assigned to 1 of 4 dietary treatments arranged in a 2 x 2 factorial approach averaging 0.64% Ca for high Ca (HCa), 0.46% Ca for low Ca (LCa), 0.47% P for high P (HP), and 0.38% P for low P (LP) on a dry matter basis. Experimental diets were fed twice daily from 3 d in milk (DIM) until 31 DIM. Intake and milk yield were recorded daily. Milk samples were collected on d 28, 29, and 30 postpartum for components analyses. Blood samples were drawn 10 d before expected calving, at calving, and at 15 and 30 DIM for serum analyses of osteocalcin, a biomarker of bone accretion, and pyridinoline, a biomarker of bone resorption. Total fecal collection was conducted when cows in a block averaged 20 DIM. Intake and production traits were not significantly affected by any of the dietary treatments. Cows averaged nearly 21 kg/d dry matter intake and 44 kg/d milk yield from 6 to 31 DIM. There were no significant differences across treatments in body weight or body condition score loss. Phosphorus intake, P fecal output, P digestibility, and P apparent absorption were affected by dietary P content. Calcium intake was higher with HCa, but Ca fecal output, digestibility, and apparent absorption showed an interaction between dietary Ca and dietary P. Calcium fecal output was 100.6 g/d for cows fed HCaHP, intermediate for cows on the HCaLP diet (89 g/d), and similar among cows fed the 2 LCa diets (70 g/d with LCaHP and 75 with LCaLP). There was no significant effect of Ca or P on osteocalcin measurements. Pyridinoline concentrations were affected by dietary Ca levels and tended to have a significant dietary Ca x dietary P interaction. Phosphorus apparent digestibility occurred independently of dietary Ca levels. Results of this study suggest that more bone was mobilized in cows fed LCa diets, but excess dietary P caused greater and prolonged bone mobilization regardless of dietary Ca content.