The effect of age and level of dietary calcium intake on calcium metabolism in sheep

Macromineral requirements for maintenance and growth in male and female hair sheep

A better understanding of the nutritional requirements of sheep, especially in terms of minerals, is crucial for improving production. We estimated the net requirements for Ca, P, K, Mg, and Na for gain (NCa_g, NP_g, NK_g, NMg_g, and NNa_g) and maintenance (NCa_m, NP_m, NK_m, NMg_m, and NNa_m) in male and female hair sheep. Six datasets with 248 individual records of hair sheep (139 non-castrated males, 75 castrated males and 34 females) were used to estimate the net macromineral requirements for gain. To estimate the net macromineral requirements for maintenance, 52 observations (26 non-castrated and 26 castrated males) were used. A meta-analytical approach was applied, using non-linear mixed effects models and the study as a random effect. Based on information criteria for model selection, heterogeneous variance functions were more likely to describe mineral requirements with a low level of model selection uncertainty. The adopted criteria allowed the choice of the best models to represent the macromineral requirements. The chosen models explained the observed variability in the sex, and the choices were based on a low level of uncertainty (w ≥ 0.90). Irrespective of sex, NCa_g and NP_g decreased with increasing BW from 10 to 30 kg and average daily gain (ADG) of 150 g/day, ranging from 1.71-1.38; 1.83-1.57; 1.82-1.51 of Ca and 0.86-0.66; 0.92-0.78; 0.92-0.75 of P for non-castrated males, castrated males, and females, respectively. The NK_g remained constant, with mean values of 0.26 g/day. The NNa_g range was 0.17 to 0.14 g/day for non-castrated males, 0.20 to 0.25 g/day for females, and constant (0.18 g/day) for castrated males with an increase in BW from 10 to 30 kg and an ADG of 150 g/day. Macromineral requirements for maintenance (mg/kg BW) and retention (%) were 23.70 and 54.30 for Ca, 25.33 and 79.80 for P, 11.74 and 5.00 for K, 2.63 and 8.50 for Mg, and 7.01 and 8.10 for Na for males. The International Committees did not provide inferences about the sex influence on mineral requirements. Our study indicates that sex is one factor that influences the macromineral requirements for gain. The information generated in this study can be used to optimize the mineral management of hair sheep in the growing phase in tropical regions.

Keel bone fractures affect egg laying performance but not egg quality in laying hens housed in a commercial aviary system

The aim of this study was to investigate the effect of keel bone fracture (KBF) severity and healing activity on individual productivity of laying hens. Focal hens (75 Lohmann Selected Leghorn (LSL), 75 Lohmann Brown (LB)) were housed alongside non-focal hens in 10 identical pens containing a commercial aviary system (15 focal hens per pen). Eggs of focal hens were identified by orally administering a dye on 3 consecutive days, resulting in a hen-specific color pattern in the yolk. Eggs were collected at 7 time points (37 to 61 weeks of age; WOA) for 5 d to determine individual laying performance and to assess egg quality. Radiographs were performed to score KBF severity on a continuous scale. Healing activity was scored as inactive, healing, or fresh. Linear mixed effects models were used for statistical analyses. We found an association between KBF severity and reduced egg laying performance with increasing age (P = 0.005). At 37 WOA, egg laying performance was similar across KBF severities, whereas at 61 WOA, performance in hens with the highest observed KBF severity was 16.2% lower than in hens without fractures. Hens with fresh fractures had a lower performance than hens with healing and inactive fractures at 37 WOA but higher performance at 61 WOA (P = 0.02). Egg quality parameters were not affected by fractures but were associated with an age × hybrid interaction (egg mass: P = 0.039, shell breaking strength: P = 0.03, shell width: P = 0.001). In conclusion, hens could maintain high performance irrespective of fracture severity until shortly after peak of lay, but seemed to redirect available resources towards fracture healing if a fresh fracture was present. At the end of lay, the negative effect of KBF fracture severity on individual production amplified indicating that hens were no longer able to cope with the physiological challenge of a fracture.

A comparative meta-analysis on the relationship of faecal calcium and phosphorus excretion in mammals

To investigate the relationship between faecal calcium (Ca) and phosphorus (P) excretion in different mammalian species, a meta-analysis on digestibility data derived from the literature was conducted. Seventy-three studies on carnivores, omnivores, large and small hindgut fermenters, ruminants and hippos (a total of 21 mammalian species, precondition for inclusion dietary Ca/P ratio 1.5/1 - 3.0/1) were analysed for Ca and P digestibility. Dietary Ca/P ratios were lower than faecal Ca/P ratios in carnivores, omnivores, ruminants and hippos. In hindgut fermenters, dietary Ca/P ratios were higher than faecal Ca/P ratios, indicating higher intestinal Ca absorption in these species. In all species investigated, there was a significant positive relationship between Ca intake and faecal Ca excretion and between P intake and faecal P excretion. In the biologically relevant range, these equations predicted lower faecal Ca losses in hindgut fermenters than ruminants, for faecal P vice versa. In all species, faecal Ca and P excretion correlated significantly. In carnivores, this highly linear correlation was exceptionally strong (R² = .92). Yet, the linearity of the correlation was questionable in omnivores and ruminants. Possibly, the strong linear correlation of faecal Ca and P excretion in carnivores is due to the formation of insoluble Ca/P complexes in their relatively short and simple gastrointestinal tract. Another hypothesis is that in carnivores, Ca homeostasis relies on modifying bone turnover to a higher degree than on changes in intestinal Ca absorption. For the formation of bone matrix, a constant ratio of Ca and P absorption is of advantage.

Lead (Pb) in sheep exposed to mining pollution: implications for animal and human health

Livestock from the ancient mining area of Sierra Madrona and Alcudia Valley (Spain) is exposed to elevated levels of lead (Pb), as previous studies based on blood monitoring have revealed. Here we have studied blood, liver and muscle Pb levels in sheep in order to know if Pb exposure could represent a risk for human consumers of the meat and offal of these animals. A cross-sectional study was conducted with ≥4 years old (adults) ewes from the mining area (n=46) and a control area (n=21). Blood samples were taken before the sacrifice at the slaughterhouse, and liver and muscle samples were taken thereafter. At the same time, 2-3 year old rams (subadults, n=17) were blood sampled in the mining area. Blood, liver and muscle Pb levels were higher in the mining than in the control area. Blood Pb concentration in the mining area (n= 44, mean: 6.7μg/dl in ewes and 10.9μg/dl in rams) was above background levels (>6μg/dl) in 73.3 percent of animals. Liver Pb concentration in 68 percent of sheep from the mining area (n=32, mean: 6.16μg/g dry weight, d.w.) exceeded the minimum level associated with toxic exposure (5µg/g d.w.) and 87.5 percent of liver samples were above European Union Maximum Residue Levels (MRL) established for offal destined for human consumption (0.5µg/g w.w.~1.4µg/g d.w.). On the contrary, none of the muscle samples in ewes exceeded the EU MRL (0.1µg/g w.w.~0.34µg/g d.w.) established for meat, which may be related to the decline of blood Pb levels with age observed in the present study. These results suggest a potential health effect for sheep exposed to Pb pollution in this area and implications for food safety, but further research with lamb meat may be necessary to refine the risk assessment for human consumers.

A note on the effects of high levels of dietary calcium, phosphorus and sodium on nutrient utilization by sheep offered a roughage-based diet

Castrated male sheep were offered a roughage without (control sheep, no. = 8) or with calcium, phosphorus and sodium (CaPNa sheep, no. = 8; Ca, P and Na intake 34, 10 and 17 g/day per sheep respectively, given twice daily as drench). Food intake and live-weight change were unaffected. Water intake and urine excretion were higher whereas dry-matter apparent digestibility, nitrogen retention and wool growth were lower in the CaPNa sheep. The excretion of allantoin in urine indicated no differences in microbial protein absorption from the gut. There were small differences in the proportions of volatile fatty acids, numbers of protozoa and mineral concentrations in rumen fluid between the sheep in the two groups. Retentions of Ca, P and Na were higher in the CaPNa sheep, whereas retention of potassium was lower.

Effect of growth rate on mineral retention and body composition of growing lambs

Groups of wether lambs were grown at different rates from about 24 kg live weight to 50 kg, by feeding them different amounts of the same concentrate diet. The slow growing lambs had higher contents of protein, ash, calcium (Ca), and phosphorus (P), and less fat and magnesium (Mg) than other groups. Differences in composition were significant between slow (120 g/day) and fast growth (230 g/day; P < 0-05) but not always between intermediate (160 g/day) and other growth rates. The differences became small and insignificant when data were expressed on a fat-free basis except for Mg which decreased with slow growth. Ash, for example, increased from 47 g/kg fat-free gain with fast growing animals to 54 g/kg with slow growth. Mg decreased from 0·44 g/kg fat-free gain with fast growth to 0·24 g/kg with slow growth. The data support the view that the ratio of ash to fat-free empty-body increases only slightly with age.

The basic diet contained 3·9 g Ca per kg dry matter and the effect of a substantial supplement of calcium carbonate on lambs growing at the fast rate was to increase their retentions of ash, Ca and P by a factor greater than 1·25. There are alternative explanations for this finding. One possibility is that the availability of Ca in the basic diet had been reduced by unknown factors. It is also possible that the supplementary carbonate altered the acid/base status of the animals and resulted in conditions which favoured skeletal mineralization.

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.

Factors influencing calcification of cardiac bioprostheses in adolescent sheep

OBJECTIVE

We determined the possible effects of age, antimineralization treatments, circulatory implant conditions, prosthesis design, and valve-related structural aspects on valve calcification in adolescent sheep.

METHODS

Calcium content was measured by means of atomic absorption spectrometry in bioprostheses implanted in 120 sheep (age <1 year) for a period of 3 or 6 months.

RESULTS

Bioprostheses calcified significantly in adolescent sheep, but the extent of calcification was multifactorial. Multivariate analysis of the calcium content reveals that age, mitral or pulmonary implant position, prosthesis design (stented or stentless), structure (porcine or pericardial, wall portion or cusp), and antimineralization treatment are independent factors influencing calcification; implant duration beyond 3 months was not. In juvenile sheep (age 5 months) the wall portion, as well as the cusps of the prosthesis, calcified significantly more than in adolescent sheep (age 11 months). Irrespective of age, the cusps of valves implanted in the mitral position calcified more than those in the pulmonary position. The wall portion of stentless valves calcified more than that of stented valves, and pericardial valves calcified less than porcine valves. The surfactant (Tween 80, No-React, and alpha-amino-oleic acid) and alcohol (ethanol and octanediol) treatment significantly reduced cusp calcification; sodium dodecylsulfate did not. None of the anticalcification treatments was able to prevent wall calcification in stentless porcine valves.

CONCLUSION

These findings suggest that tissue valve calcification is determined by many independent factors, which can be identified by using adolescent sheep as a preclinical in vivo model.

Effects of varying dietary calcium and phosphorus on growth and on composition of empty bodies and isolated bones of male kids

Two experiments, each following a two-factorial design (2 x 2), were carried out using 12 and 13 male kids initially weighing about 10 kg. Concentrations per kg dietary dry matter were 10 vs. 4 g Ca and 4.5 vs. 2.0 g P in experiment 1 as compared to 10 vs. 17 g Ca and 4.2 vs. 2.5 g P in experiment 2, respectively. In experiment 1, low Ca intake significantly reduced empty body concentrations of ash, Ca and P with no negative effect on performance traits, whereas low P intake negatively affected feed intake, growth rate and feed conversion ratio, and reduced empty body concentrations of ash, Ca, P and Mg. Low intake of either one or both of these elements increased lipid concentrations of femora, pelvis and vertebrae. In these three bones, the respective ratios Ca/P, Ca/Mg and P/Mg were decreased by low Ca intake and, to greater extents, increased by low P intake. Low intake of both elements caused less pronounced changes than low intake of P alone. In experiment 2, lowering dietary P concentration to 2.5 g/kg dry matter significantly reduced growth rates without affecting empty body concentrations of ash, Ca, P or Mg. Almost doubling Ca intake significantly increased body concentrations of ash, Ca and P at both levels of P intake without influencing growth rates.

Effects of reducing dietary cation-anion balance on calcium kinetics in sheep

A Ca kinetic study with a four-compartment model being fitted to radioisotope and balance data using the CONSAM (conversational, simulation, analysis, and modeling) computer program was conducted to examine the effects of dietary cation-anion balance, calculated as milliequivalents [(Na + K] - (Cl + S)]. Twelve crossbred wethers were used as eucalcemic control (period 1); then Ca loss during lactation was simulated by continuous infusion of ethylene glycol tetraacetate (period 2). Dietary cation-anion balance was manipulated by supplementation of various mineral salts and was +339, +35, and -127 meq of kg DM-1 during period 1 and +429, +68, and -147 meq of kg DM-1 during period 2 for control and two treatments, respectively. Animals responded to the simulated lactational Ca loss (period 2) by increasing true intestinal absorption of Ca and bone resorption and by reducing Ca accretion by bone. No difference was observed in concentration of total Ca in plasma, but treatments produced increased concentration of plasma ionized Ca during both periods. Both treatments produced hypercalciuria during both periods, and the lowest cation-anion balance increased true intestinal absorption of Ca and reduced bone accretion during period 2. The size of total exchangeable Ca pool did not differ between treatments or periods, but amount of Ca movement between the pools increased with the intermediate cation-anion balance during period 1 and with both treatments during period 2 compared with control. These results indicated that feeding reduced cation-anion balance diets increased Ca flux through the exchangeable Ca pool with no changes in the size of the pool, particularly when Ca demand was increased.

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.

Effects of dietary calcium, vitamin D3, and corn supplementation on growth performance and mineral metabolism in young goats fed whole milk diets

Twenty-four male goats, approximately 2 to 4 wk of age, were allotted to four dietary treatments in a 2 X 2 factorial design and were fed a basal milk diet at 12.5% body weight for 20 wk. Vitamin D3 was added to the milk in two different amounts with and without supplemental CaCO3. At the end of wk 7, corn was added to all diets at 1% body weight. Over 20 wk, average daily gain was unaltered by addition of Ca or vitamin D3 to the diet. When corn was added to the diet, gains increased from 48 to 180 g/d. Plasma Ca concentrations were not affected by dietary treatment. Supplemental Ca decreased plasma Mg concentrations. Corn supplementation curtailed a depression in plasma Mg and seemed to prevent a whole milk-induced hypomagnesemia. Fecal excretion of all minerals measured was increased in goats fed supplemental Ca. Dietary Ca increased urinary Ca but decreased urinary Mg. Percentage of apparent absorption of Ca, Mg, and total ash was lower in Ca-supplemented goats, as was apparent retention of Ca and Mg. The physiological responses reported suggest the goat as a potential research model for mineral metabolism studies in other ruminants.

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.

Calcium and phosphorus requirements of the ewe during pregnancy and lactation. 1. Calcium

Mineral balance and radioisotope studies have been carried out to test the adequacy of recent Agricultural Research Council (1980) recommendations for calcium and phosphorus for pregnant and lactating ewes. At the same time, Ca metabolism was compared throughout pregnancy and lactation in ewes restricted to these recommendations and in ewes given a plentiful supply of dietary Ca and P. Irrespective of their Ca intake, ewes were unable to absorb enough dietary Ca in late pregnancy and early lactation to meet the high demands, and skeletal stores of Ca were mobilized to make good the deficit. Whereas ewes given the plentiful intake absorbed enough dietary Ca in mid- to late lactation to replace their lost skeletal Ca stores, ewes given the restricted Ca and P intake did not and, at the end of lactation, were still in deficit of about 10% of their total body Ca. Since Ca absorption in the restricted ewes occurred at the maximum efficiency (66%) expected from a hay and concentrates diet, the Agricultural Research Council (1980) recommendations for Ca, particularly in mid-to late lactation, must be inadequate. It is suggested that in calculating requirements, allowance must be made for the inevitable loss and subsequent replacement of skeletal stores. The endogenous faecal loss of Ca was found to vary in direct relation to the food intake, and the significance of this finding to calculations of Ca requirements is discussed.

Calcium excretion in feces of ungulates

1. Fecal excretion of calcium was examined in 122 individual ungulates representing 7 species of Equidae, 3 species of Tapiridae, 3 species of Rhinocerotidae, 2 species of Elephantidae, 2 species of Hippopotamidae, 12 species of Bovidae, 2 species of Cervidae, 3 species of Camellidae and 1 species of Giraffidae. 2. Animals were fed timothy hay, a low calcium diet or alfalfa hay, a high calcium diet. 3. In a few cases oat straw or prairie hay was used instead of timothy hay. 4. Samples of feces were obtained from individuals daily for 4 days following a 20 day dietary equilibration period. 5. Feces of equids, tapirs, rhinoceros and elephants had a lower calcium concentration and a lower Ca/P ratio than feces of ruminants when the animals were fed diets of equivalent calcium content. 6. The findings suggest that the non-ruminant ungulate equids, tapirs, rhinoceros and elephants absorb a larger proportion of dietary calcium than ruminants do.

[Influence of age and sex on in vitro intestinal absorption of zinc and manganese]

The influence of age and sex on the intestinal in vitro absorption of the trace elements zinc and manganese was studied with SPF-Sprague-Dawley-rats. For this purpose the absorption was measured with animals of both sexes starting at once after the weaning period (17 to 20 days) until an age of maximal 80 days. The measurements were made continuously in periods of a few days. The results of a total of five experimental series show that the transfer to the serosal solution and the uptake of the intestinal wall of both elements decrease permanently with increasing age. The most severe decrease occurs, however, at an age of the rats between 20 and 40 days, that is shortly after the weaning period. The previous change of the diet, however, cannot be the main explanation for the significant alteration of the absorption. In order to test this possibility the rats were only fed with the milk of their mothers up to an age of 36 days, while the control groups received already a pelleted casein diet starting with an age of 18 days. The results of these experiments were that the milk-fed rats absorbed only somewhat more zinc or manganese than did the corresponding control groups. There were no significant differences in the amounts of Zn absorption between male and female rats.

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

1. A combination of a mineral balance and a radioisotope technique has been used to study the relationship between dose rate of 1-α-hydroxycholecalciferol (1α-OH-D3) and the magnitude and duration of its effect on the various processes of calcium and phosphorous metabolism in adult wether sheep.

2. The rate of absorption of Ca was markedly increased by treatment and maximum response occurred at the lowest dose rate.

3. Although sheep were already Ca-replete, the extra Ca absorbed was all retained and increased retention was brought about by a combination of an increase in bone accretion and a decrease in bone resorption. This finding conflicts with the generally-held belief that bone resorption is increased by cholecalciferol treatment.

4. The rates of absorption and retention of P were increased by 1α-OH-D3treatment and maximum response occurred at the lowest dose rate.

5. That P absorption could be increased by treatment suggests that not all the available dietary P was absorbed in the control period.

6. Although the loss of endogenous P in the faeces was unaltered by treatment, the secretion of P into the gut was increased, and the increase was directly related to increased serum inorganic P concentration.

7. Nearly all the extra P absorbed was retained and increased retention was achieved by a combination of an increased incorporation into and a decreased loss from the non-exchangeable pools of bone and soft tissues.

8. The time interval taken for absorption rates of Ca and P to return to normal after the end of each treatment was related to the dose rate of 1α-OH-D3. Although higher dose rates had little effect on the magnitude of response, they did prolong slightly the duration of response.

The effect of dietary protein intake on calcium metabolism of the pregnant ewe

1. The effect of protein intake on calcium metabolism has been studied in the pregnant ewe. 2. Results suggest that decreased Ca retention in protein-deficient animals was a result of a decreased rate of Ca absorption and not a decreased rate of bone accretion as suggested by other workers.

The effect of 1-alpha-hydroxycholecalciferol on calcium and phosphorus metabolism in the lactating ewe

1. The effect of 1-alpha-hydroxycholecalciferol (1 alpha-OH-D3) on calcium and phosphorus metabolism has been studied in ewes at peak lactation by a combination of a mineral balance and a radioisotope technique. 2. The rate of Ca absorption was substantially higher in the treated ewes than in controls. The rates of endogenous loss of Ca into urine, faces and milk, however, were only slightly higher. 3. In consequence, the net retention of Ca was increased and the loss of skeletal reserves of Ca normally associated with peak lactation, prevented. 4. Although the rate of bone accretion increased slightly, the increase in skeletal retention of Ca resulted mainly from a decrease in the rate of bone resorption. 5. This finding conflicts with the generally held belief that bone resorption is increased by cholecalciferol treatment. 6. The rates of apparent absorption and retention of P were increased by the treatment probably as a result of a direct effect of the 1 alpha-OH-D3 on P absorption. 7. These results provide a possible explanationof the beneficial effect of 1 alpha-OH-D3 in preventing parturient paresis (milk fever) in the dairy cow.

Adaptations in the calcium and phosphorus metabolism of sheep in response to an intravenous infusion of Ca

1. The effect on calcium and phosphorus metabolism of a high rate of Ca infused directly into the blood of Ca -deficient wethers, already receiving an adequate Ca intake, has been studied by a combination of balance and radioisotope techniques. 2. The rate of Ca retention, which was already high, increased only slightly during the infusion before it reached a maximum. The surplus Ca was compensated for by a decrease in the rate of absorption and an increase in the rate of urinary Ca excretion. 3. These findings support the theory that at maximum retention the rate of Ca absorption becomes regulated according to the rate at which Ca can be stored in bone. 4. results suggest that the decreased absorption was due to a decrease in the rate of active absorption and that the low rate remaining was due to diffusion. 5. The rate of P retention was increased by the Ca infusion, possibly as a result of the increased Ca retention.

The effect of dietary calcium intake of ewes in pregnancy on their Ca and phosphorus metabolism in lactation

1. A combination of a mineral balance and a radioactive technique has been used to study the effect of the dietary calcium intake of ewes in pregnancy on their Ca and phosphorus metabolism in lactation.

2. Ewes which had received a Ca-deficient diet in pregnancy absorbed Ca at a greater rate and with a greater efficiency in early lactation than did the control animals, which had received an adequate Ca intake in pregnancy. The apparent absorption of P was also higher in the Ca-deficient sheep.

3. Since both groups of sheep received the same high Ca intake in lactation, the increased rate of absorption of Ca must have resulted from an increased rate of active transport rather than an increased rate of diffusion.

4. Retention of both Ca and P was positive in the Ca-deficient ewes but negative in the control ewes. This difference in retention reflected a difference in bone metabolism.

5. The maximum rate of absorption possible, which is equal to the rate of irreversible loss of Ca from the rapidly exchangeable pool, was much greater in the Ca-deficient lactating ewes than was previously found in Ca-deficient wethers. This difference is due to the additional pathway of loss of Ca in the milk of the lactating animals.

6. The relationship between these findings and the prevention of milk fever in dairy cows by manipulation of the dietary Ca intake is discussed.

Studies on the absorption and retention of calcium and phosphorus by young and mature Ca-deficient sheep

1. A combination of a mineral balance and a radioactive technique has been used to study the effects of increased levels of dietary calcium and phosphorus on the Ca and P metabolism of young and mature wether sheep previously made Ca-deficient. 2. Ca absorption was directly related to Ca intake until an absorption maximum was reached. Young animals absorbed dietary Ca more efficiently than mature animals and had a much higher maximum rate of absorption. Apparent P absorption was directly related to P intake and maximum P absorption was also higher for the young animals. 3. Excretion of Ca in the urine and into the intestine was not altered by changes in Ca intake. Excretion of P in the urine, however, varied considerably and it is suggested that this process may be largely responsible for P homoeostasis. 4. Ca retention was directly related to Ca absorption. Maximum retention was considerably higher for the young animals than for the mature animals and occurred for each group of animals at exactly the same dietary intake as maximum Ca absorption. 5. Ca and P were retained in a constant ratio of 1-25:1 and the results suggested that P retention was controlled by the rate of Ca retention. 6. Bone turnover was higher for the young than for the mature animals. Animals mobilized skeletal Ca when receiving the Ca-deficient diet and replaced their Ca losses when the dietary Ca was plentiful by changing the relative rates of bone resorption and bone accretion. Although bone resorption was mainly responsible for Ca homoeostasis, bone accretion appeared to play some part in the young animals. 7. Maximum retention of Ca occurred just as the rate of bone resorption became zero and was equal to the rate of bone accretion. The lower maximum retention of Ca for mature animals was due to a lower rate of bone accretion. 8. Results suggested that when bone resorption ceased, Ca absorption was regulated by homoeostatic mechanisms at a level just sufficient to maintain maximum retention, and that the maximum rates of absorption measured may not have been true maximum rates. 9. The consequences of a relationship between bone accretion and maximum Ca retention are discussed with reference to older, pregnant and lactating animals.

The effect of growth hormone on calcium metabolism in the sheep

1. The effect of subcutaneous administration of bovine growth hormone on calcium metabolism of nearly mature wether sheep has been studied by a combination of a radioactive technique and a nutrient balance technique. 2. Administration of growth hormone resulted in a significant increase in the rates of absorption of Ca, accretion of Ca into bone, resorption of Ca from bone and skeletal retention of Ca, and also in the sizes of the exchangeable Ca pools. 3. Retention of phosphorus was also significantly increased. 4. These changes suggest that the effect of growth hormone was to alter the Ca metabolism of nearly mature wethers to resemble that of younger, more actively growing animals. 5. Results are consistent with the theory that oestrogens may alter Ca metabolism of wethers by increasing growth hormone production.

Zinc-65 absorption and tissue distribution in two- and six-month-old holstein calves and lactating cows

Holstein calves and cows in first lactation were fed a low-zinc (16.6 ppm) experimental diet. Zinc-65 absorption and tissue distribution were determined following a single oral tracer dose of zinc-65 given 14 days prior to sacrifice. Net zinc-65 absorptions for the cows and 2- and 6-mo-old calves were 53.4, 49.7 and 47.2% of the dose. Tissue zinc-65 content, adjusted for body weight and zinc-65 of milk of the cows was not significantly different from that of either age calves in 13 of 20 comparable tissues. Greatest differences in tissue zinc-65 were in tibia and rib with the 6-mo-old group highest and cows lowest. Lactation represents a major homoeostatic demand for zinc, and the intestinal absorptive ability of adult cattle remains responsive to physiological need.

The effect of changes of dietary calcium concentration on calcium metabolism in sheep

1. The effect of changes of dietary calcium concentration on Ca metabolism in eight adult wethers has been studied by the use of balance and radioactive techniques.

2. Animals receiving an adequate Ca intake absorbed sufficient Ca to supply their maintenance requirements only; a change in intake resulted in a corresponding change in the rate of absorption and disturbed this Ca balance. The new rate of absorption appeared to be determinded by the Ca concentration of the new diet and the efficiency of absorption of Ca from the previous diet.

3. Provided the new diet contained sufficient available Ca, animals quickly altered their efficiency of absorption of Ca until they were again absorbing enough for maintenance only.

4. When a lack of available Ca in the diet made it impossible for them to meet their maintenance requirements, they slowly reduced faecal endogenous excretion of Ca.

5. Ca-deficient animals absorbed Ca at a very high rate when given a diet plentiful in Ca, and absorption decreased only when all the previous losses had been restored.

6. Ca-deficient animals also mobilized Ca reserves more readily in response to a severe loss of blood Ca than did animals which were not deficient.

7. Retention of Ca was directly related to the rate of absorption of Ca and inversely related to the rate of resorption of Ca from bone.

8. The results indicate that resorption of Ca from bone is the major process involved in Ca homoeostasis and that Ca absorption is responsible for the long-term control of Ca metabolism and in particular for maintaining body Ca reserves.

Studies on the transfer of calcium across the ovine placenta and incorporation into the foetal skeleton

1. Radioactive calcium has been used to study the placental transfer of Ca in ewes at three stages of gestation.

2. At each stage virtually all the radioactive Ca injected into a foetus was still present 5–6 h later and little or none was found in the mother or in a twin foetus if present.

3. It was concluded that there is neither exchange of Ca between foetal and maternal pools nor transfer from foetus to mother. Passage of Ca across the placenta of the ewe is therefore a one-way process.

4. The rapidly exchangeable Ca pool of the foetus tended to increase in size with the stage of gestation and was found to contain only about half of the total Ca of the foetal soft tissues.

5. Two methods for calculating the rate of accretion of Ca into the foetal skeleton have been applied. The results obtained from these calculations suggested that rates of foetal bone accretion also increased with the stage of gestation. Accretion per unit foetal weight, however, remained fairly constant irrespective of age or number of foetuses present.

6. Bone accretion rates calculated from the results of the present work were very similar to the rates obtained previously for transfer of Ca across the sheep placenta, indicating that resorption of Ca from bone is negligible in the foetus.

The effect of ammonium chloride on calcium metabolism in sheep

1. A combination of balance and isotope techniques has been used to study the effects of dietary supplements of NH4Cl, given for 1 and 10 weeks, on calcium metabolism in 1- and 2-year-old wethers.

2. The main effects of the NH4C1 supplements were to decrease urinary pH, increase urinary Ca excretion and to increase Ca absorption and the percentage of dietary Ca absorbed.

3. The results were different from those obtained by other workers in man and rat, and possible explanations of this difference are discussed.

4. A difference was also found between 1- and 2-year-old animals in their long-term response to the NH4Cl supplement. This difference may have been due to a lack of available Ca in the diet of the younger animals, and prolonged ingestion of NH4C1 may increase the amounts of Ca absorbed and retained.