Salt consumption and the effect of salt on mineral metabolism in horses

The voluntary salt consumption of mature unexercised horses was measured weekly for up to 45 weeks. Voluntary intake among horses was quite variable ranging from 19 to 143 g of salt per day and was inversely related to total salt intake (salt in feeds plus voluntary intake). Mean daily voluntary salt consumption was 53 g. Season of the year did not influence voluntary intake. In preference tests which evaluated every two choice combination of 0.2% and 4% NaCl in test diets fed daily for four days, ponies generally preferred diets containing the lower amount of salt. In similar preference studies which used NaHCO3 as a sodium source, ponies always preferred the diet containing the lower level of NaHCO3. Metabolism studies employing diets containing 1, 3 or 5% NaCl showed that urinary excretion was the major excretory pathway for sodium and chloride. Fecal excretion, intestinal absorption and retention of sodium were not affected by level of salt intake. Urinary calcium excretion was unaffected by salt intake but calcium and phosphorus absorption and retention were enhanced when ponies were fed diets containing 3 or 5% sodium chloride. Magnesium and copper metabolism were unaffected by salt intake. Horses voluntarily consume relatively large amounts of sodium chloride but it is likely that not all voluntary consumption is related to the salt requirement of the horse. Habit and taste preference could also be involved. Salt consumption at the levels used in these studies does not appear to be detrimental to the metabolism of other minerals in the horse.     

Influence of high phosphorus intake on salivary and plasma concentrations,and urinary phosphorus excretion in mature ponies

This study addressed the question whether the concentration of phosphorus (P) in saliva of ponies is influenced by P intake. Six ponies were fed a diet high in P (HP treatment), providing 21 g P/day, and a diet low in P (LP treatment), supplying 7 g P/day. The two diets provided approximately 21 g calcium (Ca) and 6 g magnesium (Mg)/day. The experiment had an A‐B‐A design with treatment periods of 30 days. The ponies first received the HP diet (HP1), followed by the LP treatment and were then fed again the HP diet (HP2). Urinary P excretion was increased in both HP feeding periods and equalled approximately 7% of P intake vs. 0.5% on the LP diet. Plasma P concentration was higher for the HP treatment. The salivary P concentration ranged from 0 to 1.01 mmol P/l between ponies and there was no effect of P intake. It is suggested that saliva is not an important excretion route of P. The percentage of Ca and Mg in urine (% of intake) was higher for the LP treatment than for the HP treatments. The results of this study suggest that salivary Mg may contribute to Mg homeostasis.     

Calcium, magnesium and phosphorus absorption from the small and large intestine of ponies fed elevated amounts of aluminum

Four ileal cannulated ponies (average weight, 136 kg) were used in a replicated Latin Square experiment to determine the site and extent of calcium, magnesium and phosphorous absorption in the presence of elevated amounts of dietary aluminum. During each experimental period, ponies were fed 1.25 kg of a basal diet with or without 0.45% added aluminum as aluminum sulfate. Following an 8-day adjustment, ileal, fecal and feed samples were collected for 6-days collection. Chromic oxide (0.2% of diet) was used as an indicator to measure flow through the digestive tract. The primary site of calcium absorption was the small intestine. Adding 0.45% aluminum to the diet of ponies did not alter (P>.05) the site or efficiency of calcium absorption. Ponies fed 0.45% aluminum tended (P>.05) to absorb larger quantities of magnesium from the total digestive tract. This is probably an indirect response of aluminum on magnesium absorption rather than a direct interaction of these minerals. The major site of apparent phosphorus absorption in ponies was the large intestine with a net secretion of phosphorus into the small intestine. Aluminum decreased (P<.05) the percentage of phosphorus absorbed from the large intestine by 59%. Equine grazing forages which contain elevated concentrations of aluminum or are contaminated with aluminum-containing soil may need phosphorus supplementation.     

Copper balance in mature geldings fed supplemental molybdenum

Four mature sedentary geldings were used in a 4×4 Latin square designed experiment to evaluate the effects of supplemental molybdenum (Mo) on copper (Cu) balance. Four diets were formulated to contain 0 (control), 5, 10 and 20 ppm of supplemental Mo and were fed for a 21-day adjustment period followed by a 72-hour fecal and urine collection. Diets consisted of a pelleted concentrate based on corn, soybean meal and cotton seed hulls fed in a 50:50 ratio of concentrate to native prairie grass hay. All diets were formulated to be isonitrogenous and isocaloric with similar concentrations of Cu. Urine was collected every four hours for 72 hours and multiple fecal grab samples were taken every two hours post feeding. On the third collection day, blood samples were drawn at the time of feeding, each hour for five hours post feeding, and eight hours post feeding for serum Cu analysis. Balance data were analyzed using a general linear model procedure with horse, period and treatment as main effects. Serum Cu data were analyzed using the general linear model procedure with horse, treatment and period as main effects and time as the repeated variable. The intake of Cu was similar among all diets fed. There was no difference (p>.05) in serum Cu concentrations over time or between treatments due to supplemental Mo. Urinary and fecal excretion of Cu did not differ (p>.05) between diets. Consequently, the balance of Cu was similar among diets consumed. Excretion of Mo in the urine was higher (p<.05) in horses fed the 20 ppm Mo diet versus the 0, 5 and 10 ppm Mo diet. As Mo intake increased, fecal excretion increased (p<.05) across all diets. Additionally, Mo balance was higher (p<.05) on the 20 ppm Mo diet than all other diets. In conclusion, supplemental Mo appeared to have no adverse effect on the absorption and retention of Cu when fed to mature geldings.     

Effect of sodium phytate supplementation on fat digestion and cholesterol metabolism in female rats

The effects of sodium phytate supplementation on fat digestion and cholesterol metabolism were investigated in female rats. On the basis of an in vitro experiment showing that phytate raised the solubility of bile acids, it was predicted that phytate feeding would depress faecal bile acid excretion, raise apparent fat digestibility and elevate serum cholesterol concentrations. The experimental diets with or without sodium phytate were either cholesterol-free or cholesterol-rich and had a normal calcium concentration. Rats fed on the cholesterol-rich diet with sodium phytate showed enhanced faecal bile acid excretion, but there was no effect on fat digestibility. In rats fed the cholesterol-free diets, phytate did neither affect fat digestion nor bile acid excretion. Sodium phytate inclusion in the cholesterol-rich diet raised serum cholesterol concentrations, but reduced liver cholesterol concentration. Thus, the in vivo data do not agree with the in vitro observations. Both phytate and cholesterol feeding influenced mineral and trace element metabolism. Liver zinc concentrations were raised by phytate feeding. Cholesterol consumption reduced hepatic concentrations of copper, iron and zinc. Both phytate and cholesterol feeding reduced the apparent absorption of calcium, magnesium and phosphorus.     

Effect of calcium supplements to a maize-soya diet on the bioavailability of minerals and trace elements and the accumulation of heavy metals in growing rats

Thirty-five (five groups with seven animals each) male albino rats (initial average weight = 44 g) were fed phytate-rich diets (analysed phytic acid concentration = 6.9 g/kg) based on maize and soy bean meal (5 g Ca, 3 g P, 1.2 g Mg, 23 mg Zn, 10 mg Pb, 5 mg Cd/kg diet). Experimental diets were supplemented with 0, 2, 4, 6 and 8 g calcium from CaCO3 per kg. The supplementation of increasing amounts of calcium resulted in a dose-dependent decrease in the apparent absorption of phosphorus. Furthermore, apparent zinc absorption and femur zinc concentration were moderately decreased due to the calcium supplementation. Kidney Cd concentration was significantly lower in rats that were fed the high calcium diets in comparison with the control animals. Femur lead concentration and hepatic delta-aminolevulinic acid dehydratase, which are known to be sensitive parameters of lead accumulation remained unchanged by the different dietary treatments. Magnesium absorption as well as liver and plasma zinc concentration and activity of plasma alkaline phosphatase were also unaffected. Although calcium supplementation may lead to a decrease in the accumulation of certain heavy metals such as cadmium, the carry-over of lead was not affected under the given experimental conditions. Furthermore, calcium-phytate-zinc interactions may adversely affect zinc bioavailability in growing rats.     

The influence of calcium intake on phosphorus digestibility in mature ponies

Literature data show conflicting results on the effect of feeding high calcium (Ca) levels on phosphorus (P) digestibility in ponies. None of the studies reported involved a dose response as to the effect of Ca intake on apparent P digestibility while keeping P intake constant. Thus, the influence of high dietary Ca level on apparent P digestibility was studied in balance trials by feeding six mature ponies three different Ca levels against a constant P intake. The ponies received 148, 316 and 535 mg Ca/kg BW/day with the low, intermediate and high Ca diet. Phosphorus intake was approximately 125 mg P/kg BW and magnesium (Mg) intake was approximately 35 mg Mg/kg BW/day. The intermediate and high Ca level decreased apparent digestibility, renal excretion and retention of P when compared with the low Ca level. However, apparent digestibility and renal excretion of P were not different between the intermediate and high Ca level. The high Ca level resulted in a retention of 66 mg Ca/kg BW/day. The percentage apparent digestibility of Ca was lower for the intermediate and high Ca level compared with the low Ca level. Magnesium digestibility was not affected by high dietary Ca level. In practice, high absolute amounts of Ca should be prevented especially when low amounts of P are fed; P digestibility will be depressed and a negative P balance may occur.     

The lowering effect of high copper intake on selenium retention in weanling rats depends on the selenium concentration of the diet

The question addressed was whether the influence of dietary copper concentration on selenium metabolism depends on the amount of selenium in the diet. Weanling, male rats were fed purified diets containing either 1 (low), 4 (normal) or 42 (high) mg Cu/kg diet and either 0.03 (low), 0.05 (normal) or 1.0 (high) mg Se/kg diet in a 3² factorial design. Extra copper was added to the diets in the form of CuSO₄ · 5H₂O and selenium as Na₂SeO₃ · 5H₂O. In rats fed either the low or normal amounts of selenium, higher intakes of copper decreased the apparent intestinal selenium absorption and increased urinary selenium excretion. The effects of copper on selenium absorption, excretion and retention were not seen in rats fed the high-selenium diets. An increase in dietary copper concentrations elevated selenium concentrations in the liver and kidneys, but slightly lowered those in the spleen of rats that were fed the diets with the normal level of selenium. In rats that were fed the diets with either low or high selenium concentration, copper intake had no effect on organ selenium concentrations. Glutathione peroxidase activity in erythrocytes was raised by feeding the diets which contained either normal or high copper content instead of those that were low in copper. It is concluded that the amount of selenium in the diet determines whether or not an increase in dietary copper concentration affects selenium metabolism.     

Effects of excess calcium as a different form on mineral metabolism in rats

Excess calcium is known to affect the metabolism of other minerals. Calcium carbonate is the main source of calcium used in previous experiments that investigated excess calcium. Thus, it remains to be clarified whether other forms of calcium also have the same adverse effects. The effects of a high‐calcium carbonate diet or a high‐calcium citrate diet on mineral concentration in several tissues of rats were examined. Male rats aged 5 weeks were fed one of the experimental diets for 4 weeks. The control diet contained calcium as calcium carbonate at the requirement level. High‐calcium diets contained calcium carbonate or calcium citrate at a level of fivefold greater than the requirement level. In rats fed the high‐calcium diets, a similar decrease in phosphorus (in the plasma) and iron (in the testis, liver and femur) was observed. Hepatic copper increased in rats fed the high‐calcium diets, whereas renal copper decreased. Therefore, excess calcium affects these mineral metabolisms regardless of its form. In contrast, the high‐calcium carbonate diet increased femoral zinc and decreased femoral magnesium, but the high‐calcium citrate diet did not affect these minerals in the femur, which suggests that the effect of excess calcium on minerals partly depends on its form.     

蒸汽压片玉米对奶牛生产性能和氮磷排放影响的研究

本试验旨在研究蒸汽压片玉米对泌乳早期中国荷斯坦奶牛生产性能和氮磷排放的影响.试验采用4×4重复拉丁方设计.将8头泌乳早期中国荷斯坦奶牛随机分为4组,每组2头.4种日粮处理中蒸汽压片玉米含量分别为精料的0、10%、20%和30%.试验分4期,每期28 d.结果表明:日粮中添加蒸汽压片玉米对奶牛干物质采食量无显著影响(P＞0.05),但显著提高了饲料转化率(奶料比)(P＜0.05);显著提高了奶牛产奶量,其中20%与30%组的4%标准奶产量(FCM)产量分别比对照组提高2.78和2.87 kg·d~(-1)(P＜0.01).对乳成分无显著影响(P＞0.05);乳蛋白、乳糖、乳非脂固形物含量呈增加趋势;对营养物质的表观消化率无显著影响(P＞0.05);日粮中添加蒸汽压片玉米显著降低了乳尿素氮水平(P＜0.05).试验组奶牛氮排放量分别比对照组降低了4.23%(P＞0.05)、9.37%(P＜0.05)和10.29%(P＜0.05),磷排放量分别比对照组降低了1.93%(P＞0.05)、2.59%(P＞0.05)和5.19%(P＞0.05).因此,饲喂蒸汽压片玉米能够有效提高奶牛的生产性能,降低氮磷的排放.     

种母鸡饲粮锌和钙水平对子代雏鸡的影响

试验观测了种母鸡饲粮锌和钙水平对子代雏鸡的影响和子代的补偿作用。结果表明,母子两代饲粮都未加锌时子代雏鸡增重和采食量显著降低(P<0.01);母代饲粮未加锌而子代加锌,虽然使子代增重和采食量有所提高,但并未消除母代未加锌对子代的不良影响。母代饲粮高钙使子代增重(P<0.05)和采食量(P<0.01)显著降低。种母鸡饲粮锌水平对子代雏鸡血清碱性磷酸酶活性的遗留影响较小,而子代的补偿作用较大。种母鸡饲粮高钙对子代雏鸡血清碱性磷酸酶活性没有显著影响(P>0.05)。母子两代饲粮都未加锌时子代血清总蛋白含量最低,子代加锌有一定的补偿作用。种母鸡饲粮高钙使子代雏鸡血清总蛋白(P<0.01)、血清白蛋白(P<0.01)和血清球蛋白(P<0.05)含量显著降低。种母鸡饲粮锌水平对子代组织中锌含量的遗留影响较小,而子代加锌后的补偿作用较大。种母鸡饲粮高钙时子代雏鸡组织中锌含量没有显著变化(P>0.05)。     

Effects of diets with different calcium and phosphorus contents on the skeletal development and blood chemistry of growing great danes

The skeletal development of three groups of great dane dogs, fed a diet composed according to the published nutritional requirements for dogs (controls) or with increased calcium or calcium and phosphorus content, was examined radiographically, histologically and biochemically. The diets were fed from the time the dogs first began eating food in addition to their dam's milk, until they were 17 weeks old. Thereafter, the calcium and phosphorus intakes of the dogs in the high calcium groups were normalised for a further 10 weeks. The dogs fed the high calcium diet without a proportionally high phosphorus intake became hypercalcaemic and hypophosphataemic, and had severe disturbances in skeletal development, growth, and mineralisation which were typical for rickets. After their calcium intake was normalised the lesions of rickets resolved but osteochondrotic lesions became apparent. The dogs fed the high calcium and phosphorus diet became slightly hypophosphataemic, their growth was retarded, and they had disturbances in skeletal development resembling osteochondrosis, which had only partly resolved after 10 weeks on the normal calcium and phosphorus diet.     

Plasma and urine electrolyte and mineral concentrations in Thoroughbred horses with recurrent exertional rhabdomyolysis after consumption of diets varying in cation-anion balance

OBJECTIVE: To determine whether plasma, urine, and fecal electrolyte and mineral concentrations differ between clinically normal horses and Thoroughbreds with recurrent exertional rhabdomyolysis (RER) after consumption of diets varying in cation-anion balance. ANIMALS: 5 Thoroughbred mares with RER and 6 clinically normal mixed-breed mares. PROCEDURE: Each of 3 isocaloric diets designated as low, medium, and high on the basis of dietary cation-anion balance (DCAB) values of 85, 190, and 380, respectively, were fed to horses for 14 days. During the last 72 hours, 3 horses with RER and 3 control horses had daily urine and fecal samples obtained by total 24-hour collection. Remaining horses had urine samples collected daily by single catheterization. RESULTS: For each diet, no differences existed between horses with RER and control horses in plasma pH, electrolyte concentrations, and creatine kinase activity or in urine pH and renal fractional excretion (FE) values. Plasma pH, strong ion difference, bicarbonate and total carbon dioxide concentrations, and base excess decreased and plasma chloride and ionized calcium concentrations increased with decreasing DCAB. Urine pH decreased with decreasing DCAB. The FE of chloride and phosphorus were greatest for horses fed the low diet. The FE values for all electrolytes exept magnesium did not differ between urine samples obtained by single catheterization and total 24-hour collection. Daily balance of calcium, phosphorus, sodium, chloride, and potassium did not differ significantly among horses fed the various diets. CONCLUSIONS: In clinically normal horses and in horses with RER, the DCAB strongly affects plasma and urine pH and the FE of sodium, potassium, chloride, and phosphorus.     

Nutrient intake, acid base status and growth performance of growing male buffalo calves fed varying level of dietary cation anion difference

Influence of + 110, + 220 and + 330 mEq/kg of dry matter (DM) dietary cation anion difference (DCAD) on growth performance of growing male buffalo calves was examined in a randomized complete block design. Three DCAD diets were randomly allotted to three groups, ten calves in each group. A linear increase in nutrient intake was recorded with increased DCAD level. However, digestibilities of nutrients remained unaltered across all diets. Calves fed + 330 DCAD diet had higher nitrogen balance than those fed + 110 DCAD diet. Blood pH and serum HCO₃ increased with increased DCAD level. Serum chloride was high in calves fed + 110 DCAD diet, while serum (Na + K) − (Cl + S) increased linearly with increased DCAD level. Serum calcium increased with decreased DCAD level while serum magnesium and phosphorus remained unaffected. Ca balance remained unaltered by calves fed varying level of DCAD. Urine pH increased with increased DCAD level. Calves fed + 220 and + 330 DCAD diets gained more weight than those fed + 110 DCAD diet. In conclusion, increased DCAD level not only increased dry matter intake but also weight gain in growing buffalo calves.     

High versus low protein diets to mink--postprandial plasma urea and creatinine response, osmotic load and pattern of nitrogen and electrolyte excretion.

Nitrogen balance, pattern of excretion of nitrogenous end-products, endogenous urinary N excretion, postprandial plasma urea and creatinine, osmotic load, urinary electrolyte excretion and water intake/output relationships were studied in 12 adult female mink fed a high protein diet (HP; n = 6) providing about 155 g protein/kg or a low protein diet (LP; n = 6) providing about 95 g protein/kg. Two balance periods of each 3 d were used and diets were fed raw or cooked. After the last balance period followed a 48 h fasting period. Postprandial plasma urea and creatinine were studied for 48 h following a test meal given after an overnight fast. Osmotic load was determined based on collection of non-acidified urine carried out during 48 h. Level of protein supply did not affect N balance, being close to zero, whereas slightly negative balances were achieved for fasting animals. Protein supply was clearly reflected in excretion of urinary urea and allantoin but not in creatinine and uric acid. Endogenous urinary N excretion was estimated by a second order regression equation giving an intercept of 280 mg/kg0.75. Post-prandial plasma urea concentrations were strongly influenced by protein supply, HP animals having substantially higher peaks than LP animals, but values returned to fasting values within 24 h after the test meal. Plasma creatinine followed a biphasic pattern with a peak about 2 h after feeding and a nadir approximately 6 h after feeding. Physical form of diet influenced postprandial urea, animals fed raw diets having a higher peak, but not creatinine. The HP diet provided almost the double osmotic load of the LP diet and a corresponding increase in urine volume. The resulting water balances were identical irrespective of diet, showing that water intake/output relationships are very accurately regulated.     

Clinicopathology of gout in growing layers induced by high calcium and high protein diets

1. An experiment was conducted to test the independent and combined effects of high dietary calcium and protein concentrations on the induction of visceral gout in growing birds of a layer strain. 2. One hundred and sixty healthy birds were randomly divided into 4 groups at 35 d of age. The different groups were given 4 diets containing normal or high concentrations of dietary calcium or crude protein in a 2 x 2 factorial experiment for 30 d. The diets contained normal calcium (Ca) and crude protein (CP) (NCNP, 8.5 g Ca/kg and 175g CP/kg), high calcium and normal protein (HC, 36.3 g Ca/kg and 175 g CP/kg), normal calcium and high protein (HP, 8.8 g Ca/kg and 245 g CP/kg) or high calcium and high protein (HCHP, 36.8 g Ca/kg and 242 g CP/kg), respectively. 3. Typical visceral gout was induced by the HCHP diet. The HCHP and HC diet caused severe kidney damage. The HP diet did not cause kidney damage, but significantly increased plasma uric acid and inorganic phosphorus concentrations. 4. The HC diet significantly increased plasma uric acid, calcium and sodium, but significantly decreased plasma inorganic phosphorus, potassium and magnesium concentrations. The HCHP diet significantly increased plasma uric acid, calcium and sodium. 5. Urine volumes were significantly higher on the HCHP and HC diets than on the control. The growers raised on HC and HCHP diets had significantly higher total quantity of 24 h urinary excretion of uric acid, calcium, magnesium, inorganic phosphorus and potassium and a significantly lower 24 h urinary excretion of sodium. The growers fed on the HP diet had a higher 24 h urinary excretion of uric acid and inorganic phosphorus than the control. 6. It is concluded that growing layer birds should not be fed on layer rations.     

Faecal bacterial profile,nitrogen excretion and mineral absorption in healthy dogs fed supplemental oligofructose

In a cross-over trial, five healthy dogs were fed a dry food without or with 1% (w/w) oligofructose to assess any oligofructose-induced effects on the faecal bacterial profile, nitrogen excretion and mineral absorption. The diets were given for a period of 3 weeks. Oligofructose feeding significantly raised the number of Bifidobacteria, Streptococci and Clostridia in faeces. The numbers of faecal anaerobic and aerobic bacteria were raised after ingestion of oligofructose. The faecal pH was unchanged. There was no effect of oligofructose feeding on the route of nitrogen excretion which was associated with a lack of effect on faecal ammonium and urinary urea excretion. It is suggested that the absence or presence of an effect of oligofructose on urinary and faecal nitrogen excretion depends on the background composition of the diet, in particular the content of non-digestible, fermentable carbohydrates. In the diets used, the content of non-digestible, fermentable carbohydrates was not measured. Both apparent magnesium and calcium absorption were significantly raised by oligofructose feeding, but phosphorus absorption was unaffected. The data presented may contribute to the qualification of the use of oligofructose in dog foods.     

The role of experience in the development of selective zinc intake in pullets

Selective food intake behaviour was studied in pullets that were subjected to different zinc supply in early life. During the first four weeks post-hatching three groups, totaling 72 birds, were fed either a low zinc diet (25 ppm), a complete diet (50 ppm) or both diets in a choice situation. The prior feeding experience was investigated during the subsequent ontogenetic development in two-choice dietary tests. Chicks first exhibited a preference for the high zinc diet as deficiency symptoms can be seen in depleted birds. Juvenile pullets did not prefer any diet for the duration of experimental period. Layers were initially indifferent to the supplemented zinc diet, but after reaching high laying capacity they began preferentially to select the complete diet. The results indicate that early experience with diets different in zinc content have no influence on subsequent diet preferences at choice. The ability to select is based on association learning following ingestion. A conditioned diet aversion first developed in phases of high zinc requirement as a result of negative feedback mechanisms produced by the deficient diet.     

Characterization of acid-base disturbances and effects on calcium and phosphorus balances of dietary fixed ions in pregnant or lactating does

Effects of fixed cation-anion balance on acid-base status and calcium and phosphorus balances were examined. Pregnant and lactating goats were fed a diet of alfalfa hay, concentrate and minerals to vary the cation-anion balance [meq sodium (Na) + meq potassium (K)-meq chloride (Cl)]/100 g diet dry matter (DM) over the range found in ruminant feeds. Small but significant effects on ruminal pH, fermentation and dilution rate were observed. Metabolic acid-base status of pregnant and lactating goats was normal when (Na + K - Cl) balance was 40 to 50 meq/100 g DM. The other treatments drastically altered plasma electrolyte concentrations, causing metabolic acid-base disturbances and profound changes in calcium and phosphorus metabolism. Subclinical hypernatremic, hypochloremic metabolic alkalosis was induced by a dietary fixed cation excess (Na + K - Cl) of greater than 85 meq/100 g DM (typical of buffered, alfalfa diets) and caused hypocalciuria, diminished calcium and phosphorus absorption, and possibly diminished dietary calcium absorption and resorption of calcium from bone. Subclinical hyperchloremic, hyponatremic metabolic acidosis from a diminished dietary fixed cation-anion balance (Na + K - Cl) of less than 10 meq/100 g DM (typical of nonbuffered corn silage or grain diets) caused hypercalciuria, enhanced calcium and phosphorus absorption and apparently enhanced calcium resorption from bone. Apparent effects on absorption and resorption depended on calcium and phosphorus intakes. Alterations in goats performance were not demonstrable. Dietary excesses of fixed cations over anions (meq Na + K - Cl/100 g diet DM greater than 50) cause metabolic alkalosis in ruminants, whereas fixed anion excesses (meq Na + K - Cl/100 g diet DM less than 40) cause metabolic acidosis. Content of electrolytes in diets should be reported in all nutrition trials with ruminants for assessment of metabolic acid-base status.     

Faecal calcium excretion does not decrease during long‐term feeding of a low‐calcium diet in adult dogs

According to a previous meta‐analysis, adult dogs do not notably increase calcium absorption from the gastrointestinal tract when calcium intake is decreased. This results in a negative calcium balance even with a moderate calcium reduction. In this study we wanted to verify (i) whether a negative calcium balance occurs at a calcium intake equivalent to NRC (2006) (Nutrient requirements of dogs and cats, 2006, The National Academies Press, Washington, DC) minimal requirements, and if so (ii) whether the negative calcium balance will persist for up to 6 months on a low‐calcium diet. After a pre‐feeding period of at least 18 weeks with calcium intake slightly exceeding maintenance requirements (200 mg/kg body weight^0.75), 12 dogs (6 Beagles, 6 Foxhound crossbreds) were fed a low‐calcium diet for 28 weeks. One dog was removed from the trial for reasons unrelated to the study at week 23. Calcium intake amounted to 60 mg/kg body weight^0.75 corresponding to the minimal requirement for maintenance in dogs (NRC, 2006 (Nutrient requirements of dogs and cats, 2006, The National Academies Press, Washington, DC)). Digestion trials were carried out at week 7, 14, 21 and 28 of the low calcium feeding period. At these time points, and at week 18 of the pre‐trial, blood samples were taken and analysed for calcium, ionised calcium, phosphorus, parathyroid hormone, vitamin D, serum crosslaps and bone alkaline phosphatase. Apparent calcium digestibility was negative throughout the study, suggesting a negative calcium balance. There was no systematic decrease in faecal calcium excretion. Serum calcium, ionised calcium and phosphorus remained within the reference range. Serum crosslaps increased continuously from baseline to week 28 of trial, with averages increasing from 0.102 ng/ml to 0.279 ng/ml, suggesting osteoclastic activity, indicative of calcium mobilisation from the skeleton. The study supports the theory of a lack of adaptation of intestinal calcium absorption from diets with relatively low calcium content in dogs. This agrees with clinical findings in dogs eating low‐calcium diet.