Effects of ammonium chloride and sulfate on acid-base status and calcium metabolism of dry Jersey cows

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.

Water Quality for Grazing Livestock I

Water is the most important nutrient for rangeland livestock. However, competition with municipalities, industry, and other water users often results in grazing livestock being forced to use water supplies that are less than perfect. Surface water in western rangleands are often contaminated by mineral extraction, irrigation runoff and other human activities. Mineral contaminants in drinking water are additive with similar contaminants in feedstuffs. The goal of this and the subsequent article is to provide producers and veterinarians with the basic background to make informed decisions about whether a given water supply is "safe" for livestock.

Renal Evaluation in Common Variable Immunodeficiency

Introduction

Common variable immunodeficiency (CVID) comprises a heterogeneous group of disorders characterized by impaired antibody production. Kidney involvement in CVID is described in isolated and sporadic case reports. The objective of this study was to study the renal function pattern in CVID patients through glomerular and tubular function tests.

Methods

Study of 12 patients with CVID diagnosis and 12 healthy control individuals. Glomerular filtration rate (GFR), fractional excretion of sodium (FE_Na⁺) and potassium (FE_K⁺), urinary concentration, and acidification capacity were measured. In addition, microalbuminuria and urinary monocyte chemoattractant protein-1 (MCP-1) were evaluated as markers of selectivity of the glomerular barrier and inflammation, respectively.

Results

In relation to glomerular markers, all CVID patients had normal GFR (>90 mL/min/1.73 m²), and microalbuminuria and urinary MCP-1 levels were also similar to those of controls. Interestingly, CVID patients had reduced urinary concentration capacity, as demonstrated by lower U/P_Osm ratio, when compared to controls. Also, while all control subjects achieved a urinary pH less than 5.3, no CVID patients showed a decrease in urinary pH to such levels in response to acid loading with CaCl₂, characterizing impaired urinary acidification capacity.

Conclusion

Patients showed a trend towards an elevated prevalence of tubular dysfunction, mainly related to urinary acidification and concentration capacities.

Dietary cation-anion difference and day length have an effect on milk calcium content and bone accretion of dairy cows

Milk and dairy products are an important source of Ca for humans. Recent studies have shown fluctuations in cow milk Ca content during the year in France, with high values in winter and with corn silage diets, and a decrease during May and June and with grass diets. The aim of this study was to identify the reasons for this seasonal decrease in milk Ca content by testing the effect of 2 levels of dietary cation-anion differences (DCAD; 0 mEq/kg of dry matter for DCAD 0 and 400 mEq/kg for DCAD 400) and 2 day lengths (8 h of light/d for short days: SD; and 16 h/d for long days: LD) on the Ca balances of dairy cows. The DCAD treatments were designed to mimic diets based either on corn silage or on herbage. The cows were only illuminated by solarium lights providing UVA and UVB. The trial was conducted according to 2 simultaneous replicates of a 4×4 Latin square design using 8 dairy cows averaging 103±44 d in milk with 4 periods of 14 d. Data were analyzed by ANOVA with a model including treatment, cow, and period effects. No significant interaction was found between day length and DCAD treatments. With DCAD 400 compared with DCAD 0, blood pH increased and plasma ionized Ca content decreased, whereas the plasma total Ca content did not differ between treatments. Milk Ca content, however, increased with DCAD 400 compared with DCAD 0, in relation to a decrease in the amount of Ca excreted in urine. The DCAD had no significant effect on protein and casein contents and DCAD 400 tended to decrease milk yield. This illustrates that the udder did not decrease Ca uptake from the blood at high DCAD even though DCAD 400 decreased the mammary availability of Ca by decreasing the proportion of blood ionized Ca. Milk Ca and casein contents were significantly lower with LD compared with SD, whereas day length had no effect on milk yield after 14 d of treatment. Bone accretion of cows increased when the Ca content of milk increased (i.e., with DCAD 400 compared with DCAD 0 and with SD compared with LD). This work suggests that long and sunny days could explain part of the seasonal decrease in milk Ca content in summer and refutes the hypothesis that low milk Ca contents at grazing could be due to the high DCAD of herbage.

Timothy hays differing in dietary cation-anion difference affect the capability of dairy cows to maintain their calcium homeostasis

Forages low in dietary cation-anion difference (DCAD) can be used to decrease the DCAD in prepartum diet but the extent to which DCAD needs to be reduced is of recent interest. The objective of this study was to evaluate the effectiveness of timothy hays differing in DCAD at maintaining Ca homeostasis. Six nonlactating and nonpregnant multiparous Holstein cows were fed diets containing timothy (Phleum pratense L.) hay with DCAD values of 4.1 +/- 3.6 (LOW), 14.1 +/- 3.0 (MED), or 25.1 +/- 2.5 (HIGH) mEq per 100 g of DM in a duplicated 3 x 3 Latin square design with 14-d experimental periods. The LOW and MED hays were produced by fertilizing established timothy fields at a rate of 224 kg CaCl(2) per ha, and HIGH hay was obtained from the same field where LOW hay was produced, but from a section not fertilized with CaCl(2). Experimental diets, containing LOW, MED, or HIGH timothy hay at 71% of dietary DM, had DCAD values of 0.7, 7.3, and 14.4 mEq per 100 g of DM, respectively. Animals were fed at 6% of metabolic body weight, which provided 108% of their daily energy requirement. For each period, after a 12 d diet adaptation, cows were subjected to an EDTA challenge (3 cows each on d 13 and 14). Infusion of EDTA solution into the jugular vein decreases the concentration of blood ionized Ca, and the EDTA challenge protocol determined the resistance time and recovery time: the time required for the blood ionized Ca concentration to decrease to 60%, and the time required to recover to 90% of the prechallenge concentrations, respectively. Urine pH was lower when cows were fed LOW compared with HIGH diet (6.88 vs. 7.83), but urine pH when cows were fed MED diet (7.15) did not differ from that when cows received the LOW or HIGH diet. However, immediately before the EDTA challenge, blood pH was lower when cows were fed LOW or MED compared with HIGH diet (7.44 vs. 7.47). Although the resistance time was not affected by treatments, the recovery time was shorter when cows were fed the LOW compared with MED or HIGH diet (185 vs. 248 and 263 min, respectively). Blood pH decreased when cows were fed the LOW or MED diet, but the capability to maintain Ca homeostasis was enhanced only when cows received the LOW diet, in which the DCAD value was decreased to 1 mEq per 100 g of DM.

Use of dietary cation anion difference for control of urolithiasis risk factors in goats

OBJECTIVE

To determine correlations between dietary cation anion difference (DCAD) and urine pH, urine specific gravity, and blood pH in goats.

ANIMALS

24 crossbred goat wethers.

PROCEDURES

Goats were randomly assigned to 1 of 4 DCAD groups (-150, -75, 0, or +75 mEq/kg of feed) and fed pelleted feed and ground hay for 7 days. The diet was then supplemented with ammonium chloride to achieve the assigned DCAD of each group for 7 days. Urine was obtained for pH and specific gravity measurements at hours -3 to -1, 1 to 3, 5 to 7, 9 to 11, and 13 to 15 relative to the morning feeding. Blood pH was determined on alternate days of the study period.

RESULTS

Goats in the -150 and -75 mEq/kg groups had a urine pH of 6.0 to 6.5 two days after initiation of administration of ammonium chloride, and urine pH decreased to < 6.0 by day 7. Goats in the 0 mEq/kg group had a urine pH from 6.0 to 6.5 on day 5, whereas urine pH in goats in the +75 mEq/kg group remained > 6.5 throughout the trial. Urine specific gravity differed only between the -150 mEq/kg and the -75 mEq/kg groups. Blood pH in the -150 mEq/kg group was significantly lower than that in the other groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Goats in the 0 mEq/kg DCAD group had a urine pH of 6.0 to 6.5 five days after intitiation of feeding the diet, and that pH was maintained through day 7, without significant reduction in blood pH. This may serve as a target for diet formulation for the prevention of urolithiasis.

Effect of Dietary Cation-Anion Difference and Dietary Crude Protein on Milk Yield, Acid-Base Chemistry, and Rumen Fermentation

Eight primiparous lactating Holstein cows (47 +/- 10 d in milk) fitted with ruminal cannulae were used to determine the effect of dietary cation-anion difference (DCAD) and dietary crude protein (CP) concentration on milk yield and composition, acid-base chemistry, and measures of N metabolism in lactating dairy cows. Treatments were arranged as a 2 x 2 factorial in a randomized complete block design to provide 15 or 17% CP and DCAD of 25 or 50 mEq (Na + K - Cl)/100 g of feed dry matter [15 or 39 mEq (Na + K) - (Cl + S)/100 g of feed dry matter]. High DCAD improved dry matter intake, milk yield, and concentrations of milk fat and protein. An interaction of DCAD and CP was observed for uric acid excretion, an indicator of microbial protein yield. Uric acid excretion was higher for high DCAD than for low DCAD in low CP diets and was similar for low and high DCAD with high CP. Serum bicarbonate concentration, urinary bicarbonate excretion, blood pH, and serum Na were elevated for high DCAD compared with low DCAD. Fractional excretion of Na, K, Cl, and Ca increased for high DCAD. Blood urea N and urinary urea N were greater for high than for low CP diets. No differences due to DCAD were observed for these parameters. Results of this study suggest that, in early lactation cows, blood acid-base chemistry is altered by differences in DCAD that range between the high and low ends of the desired DCAD range. Modifications of acid-base chemistry and the corresponding changes in protein metabolism may allow for more efficient feeding of protein and better nutritional management of the lactating dairy cow.

Biomarkers for the activation of calcium metabolism in dairy cows: elevation of tartrate-resistant acid phosphatase activity by lowering dietary cation-anion difference is associated with the prevention of milk fever

In our previous study, it was demonstrated that the administration of anion salts, which slightly lower the dietary cation-anion difference (DCAD), in the prepartum period is safe and effective for preventing milk fever in multiparous cows. In the present study, several biomarkers, which might show activation of Ca metabolism, were analyzed using stored samples in the previous study to investigate the mechanism of the preventive effect on milk fever by lowering DCAD. Changes in bone-specific alkaline phosphatase activity, osteocalcin and insulin-like growth factor I concentrations in serum were almost the same among the three groups of multiparous cows with or without the oral administration of anion salts, while the levels of these serum biomarkers in the group of primiparous cows (heifer group) were much higher compared with those in the three multiparous groups throughout the experimental period. Urinary deoxypyridinoline excretion was not a useful biomarker for dairy cows because it hardly changed during the peripartum period in all groups. However, serum tartrate-resistant acid phosphatase (TRAP) activity, which is known as a biomarker of osteoclast activity, was well associated with the administration of anion salts lowering DCAD because among the three multiparous groups, only the group of multiparous cows fed the anion salts (anion group) showed an increased level, which rose to the level in the heifer group, and was markedly higher than those in the other control groups of multiparous cows. The increased activity of serum TRAP in the anion group suggested that Ca in the plasma pool was mobilized smoothly from bone-bound Ca via mature osteoclasts at parturition, which might be due to prior activation under mild acidosis induced by slightly lowering DCAD. Therefore, TRAP was the best biomarker to monitor the activation of Ca metabolism in dairy cows fed anion salts.

Dietary Cation-Anion Difference and Dietary Protein Effects on Performance and Acid-Base Status of Dairy Cows in Early Lactation

Our objective was to examine the effects of dietary cation-anion difference (DCAD) with different concentrations of dietary crude protein (CP) on performance and acid-base status in early lactation cows. Six lactating Holstein cows averaging 44 d in milk were used in a 6 x 6 Latin square design with a 2 x 3 factorial arrangement of treatments: DCAD of -3, 22, or 47 milliequivalents (Na + K - Cl - S)/100 g of dry matter (DM), and 16 or 19% CP on a DM basis. Linear increases with DCAD occurred in DM intake, milk fat percentage, 4% fat-corrected milk production, milk true protein, milk lactose, and milk solids-not-fat. Milk production itself was unaffected by DCAD. Jugular venous blood pH, base excess and HCO3(-) concentration, and urine pH increased, but jugular venous blood Cl- concentration, urine titratable acidity, and net acid excretion decreased linearly with increasing DCAD. An elevated ratio of coccygeal venous plasma essential AA to nonessential AA with increasing DCAD indicated that N metabolism in the rumen was affected, probably resulting in more microbial protein flowing to the small intestine. Cows fed 16% CP had lower urea N in milk than cows fed 19% CP; the same was true for urea N in coccygeal venous plasma and urine. Dry matter intake, milk production, milk composition, and acid-base status did not differ between the 16 and 19% CP treatments. It was concluded that DCAD affected DM intake and performance of dairy cows in early lactation. Feeding 16% dietary CP to cows in early lactation, compared with 19% CP, maintained lactation performance while reducing urea N excretion in milk and urine.

The impact of dietary cation anion difference (DCAD) on the acid-base balance and calcium metabolism of non-lactating, non-pregnant dairy cows fed equal amounts of different anionic salts

We evaluated the impact of the dietary cation-anion difference (DCAD) on the influence of anionic salts (AS) on the metabolism of dairy cows using a study-design that included control of feed intake. Ten mature, non-lactating, non-pregnant, Holstein-Friesian-crossbreed cows received 2000 mEq of either one of the seven anionic salts tested, two combinations of the anionic salts or water as control via a rumen cannula. Salts and controls were assigned in a 10×10 Latin square design. Whole blood, serum and urine samples were taken during treatment (TP) and washout period. Samples of whole blood were tested for pH, base-excess and bicarbonate concentrations. In urine, pH and net acid-base excretion (NABE) were analysed. Calcium was measured in serum and urine. According to the different batches of hay, five groups of DCAD were created regarding cluster analysis. Changes in urine and blood parameters were statistically analysed for each DCAD group separately. The different DCAD had an impact on the amount of change in acid-base balance (ABB) and calcium metabolism and for how long these changes lasted. In the DCAD group receiving the highest amount of AS (239 mEq/kg dry matter with AS), changes of ABB were only noticeable in urine and these changes only differed from day zero in the first week of TP (P<0·05). In the other four groups changes of ABB were also visible in blood parameters, but only on a few days of TP did the deviations differ significantly (P<0·05) from day zero. Changes of ABB parameters in urine samples were more pronounced than those in blood and differed clearly from day zero (P<0·05). Parallel to the changes of ABB, calcium concentrations in these samples were significantly increased (P<0·001) in all DCAD groups. Except for the highest DCAD group, ionized calcium concentrations changed over time (P<0·020). However, the differences were very small and only differed from day zero on a few TP days. We conclude that the DCAD of a dairy cow's diet has an important impact on the effect of AS on ABB and calcium metabolism with respect to the duration and amount of change. The target regions of DCAD should be clearly below 100 mEq/kg dry matter to ensure the desired effect on ABB and calcium metabolism. Extremely negative DCAD should be avoided to minimize the risk of clinical acidosis induced by AS.

Effect of Dietary Cation-Anion Difference and Dietary Crude Protein on Performance of Lactating Dairy Cows During Hot Weather

Thirty-two lactating Holstein cows (225 +/- 63 d in milk) were used in a 6-wk trial to determine the effect of dietary cation-anion difference (DCAD) and dietary crude protein (CP) concentration on milk and component yield, acid-base status, and serum AA concentrations during hot weather. Treatments were arranged as a 2 x 2 factorial within a randomized complete block design to provide 15 or 17% CP and a DCAD of 25 or 50 mEq (Na + K - Cl)/100 g of dry matter (DM). A DCAD x CP interaction was detected for milk yield; milk yield was less for high DCAD than for low DCAD for the high-CP diets. No differences were noted at low dietary CP. Milk fat percentage was greater for high DCAD than for low DCAD, and high-CP diets supported greater milk fat percentage than low-CP diets. No differences were observed among treatments for dry matter intake or milk protein percentage. Serum total AA and essential AA concentrations and ratio of essential AA:total AA were greater for high DCAD. These results suggest that increasing DCAD improves AA availability for protein synthesis by taking the place of AA that would otherwise be used for maintenance of acid-base balance. A better understanding of the mechanisms behind this AA-sparing effect will improve management of protein nutrition in the lactating dairy cow.

Preventive Effect of Mildly Altering Dietary Cation-Anion Difference on Milk Fever in Dairy Cows

In the present study, we examined whether mildly altering dietary cation-anion difference (DCAD) contributes to the prevention of milk fever in dairy cows. Thirty multiparous cows and ten primiparous cows (heifer group) were used in this study and the multiparous cows were randomly divided into three groups of ten animals each (anion, non-anion and control groups). The cows in the anion group were given supplemental salts that slightly lowered DCAD. These salts consisted of 115 g of CaCO3, 42 g of CaHPO4, 65 g of MgSO4 x 7 H2O and 80 g of CaCl2 x 2 H2O as a daily dose for each cow, using a catheter from 21 days before the expected date of parturition until parturition. The cows in the non-anion group were given only the same Ca, Mg and ip supplement but no sulfate and chloride salts as that in the anion group. The cows in the control and heifer groups were not given any additional supplement. The incidence of hypocalcemia in the anion group decreased to approximately half of those in the non-anion and control groups, while the heifer group did not develop hypocalcemia at all. In addition, the number of days spent for the treatment of hypocalcemia and the number of drug bottles (calcium borogluconate solution) used for the treatment decreased to less than half in the anion group compared with those in the non-anion and control groups. At parturition, the serum Ca concentration in the control (6.2 +/- 1.9 mg/dl, mean +/- standard deviation) and non-anion groups (6.4 +/- 1.7 mg/dl) were significantly lower than that in the heifer group (8.3 +/- 0.4 mg/dl), and the level in the anion group was intermediate (7.3 +/- 1.3 mg/dl). The change in ionized Ca concentration was almost the same as that in serum Ca concentration, but only the concentration in the anion group tended to increase slightly from a week before parturition and was significantly higher than that in all other groups three days before parturition. Urinary pH in the anion group was maintained at a mildly acidic level (6.8-7.0) for the last two weeks before parturition, compared with those in the control (7.3-7.5) and non-anion groups (7.9-8.1), and similar to that in the heifer group (6.3-7.3). The urinary Ca excretion was the highest in the anion group among all groups during the prepartum period. There were no specific changes in the excretion of parathyroid hormone and 1,25-dihydroxyvitamin D in all groups of multiparous cows while the levels of these hormones remained low in the heifer group throughout the experimental period. The data in the present study indicates that the administration of anion salts that slightly lowered DCAD in the preparum period was effective for preventing milk fever in multiparous cows. Safe and mild metabolic acidosis induced by the anion salts could be evaluated by urinary pH (6.8-7.0), and might increase the responsiveness to Ca requirement at parturition through some complex mechanisms unrelated to the excretion of Ca-related hormones. In addition, it was clarified that primiparous cows have a high potential to respond to sudden Ca demand unrelated to hormone excretion, and their Ca metabolism was in some respects similar to that in multiparous cows fed anion salts. Therefore, manipulating mildly DCAD is expected to be an effective, safe and natural method for preventing milk fever in dairy cows.

Impact of Lowering Dietary Cation-Anion Difference in Nonlactating Dairy Cows: A Meta-Analysis

A meta-analysis of previous studies was performed to clarify the response of prepartum dairy cows to lowering dietary cation-anion difference (DCAD) and to compare different equations that have been proposed to calculate DCAD. Twenty-two published studies containing 75 treatment groups met criteria for inclusion in the meta-analysis. Five different equations used to calculate DCAD were compared for their association with clinical milk fever and urinary pH. The DCAD equation (Na + K) - (Cl + 0.6 S) was the most highly associated with clinical milk fever (R(2) = 0.44) and urinary pH (R(2) = 0.85). Lowering DCAD reduced clinical milk fever but also reduced DM intake. Lowered DCAD was associated with reduced urinary pH, blood bicarbonate, and blood CO(2), suggesting a metabolic acidosis with respiratory compensation. Blood pH was very slightly lowered by lowered DCAD. Lowering DCAD increased ionized Ca in blood before and at calving. The model predicted that lowering DCAD from +300 to 0 mEq/kg reduced risk for clinical milk fever from 16.4 to 3.2%, reduced urinary pH from about 8.1 to 7.0, and reduced DM intake by 11.3%.

Chronic toxicity and carcinogenicity of dietary administered ammonium sulfate in F344 rats

Chronic toxicity and carcinogenicity studies of ammonium sulfate, used as a food additive in fermentation, were performed in male and female Fisher 344 rats at dietary concentrations of 0%, 0.1%, 0.6% and 3.0% in a 52-week toxicity study and 0%, 1.5% and 3.0% in a 104-week carcinogenicity study. Treatment with ammonium sulfate caused significant increase in kidney and/or liver weights in males and females of the 3.0% diet group, but no effects were found on survival rate, body weights, and hematological, serum biochemical or histopathological parameters at any dose levels in the chronic toxicity study. Regarding carcinogenicity, ammonium sulfate did not exert any significant influence on the incidences of tumors in any of the organs and tissues examined. It was concluded that the no observed adverse effect level of ammonium sulfate was the 0.6% diet, which is equivalent to 256 and 284 mg/kg b.w./day in males and females, respectively, and the compound is non-carcinogenic under the conditions of the study.

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

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

Long-term effects of dietary anion-cation balance on acid-base status and bone morphology in reproducing ewes

The beneficial effects of anionic salts on calcium metabolism have been shown by supplementing rations with such salts during the last 3 weeks of pre-partum. However, there are few reports on the effects of anionic salts supplementation for periods of 4 weeks or longer on acid-base status, mineral metabolism and bone morphology. This study was conducted to evaluate the effects of the long-term dietary supplementation of anionic salts on the acid-base status, plasma minerals concentrations and bone morphology in sheep. Twenty-seven twin-bearing sheep were assigned to two experimental groups and a control group, depending on dietary cation-anion difference (DCAD) (+272.6, -88.9 and + 164.5 mEq/kg DM, respectively). Sheep assigned to each dietary treatment received their respective rations beginning 6 weeks prepartum and continuing until 12 days post-partum. Diets containing anionic salts induced a mild metabolic hyperchloraemic acidosis from 1 week pre-partum to 2 days post-partum that was completely compensated by non-respiratory mechanisms. These changes on acid-base status were accompanied by an increase of plasma ionized calcium levels. Plasma total calcium, phosphorus and magnesium concentrations were not affected by dietary treatment. Parathyroid hormone concentrations were related to the concentration of ionized calcium of plasma and were higher in sheep fed the cationic diet. Plasma osteocalcin levels were increased in sheep fed the anionic diet and cortical bone remodelling occurred in all the animals during late pregnancy in light and electron microscopy observation, but was particularly evident in the sheep fed the anionic diet. Bone turnover might be stimulated because of the role of the bone in buffering systemic acidosis. The data suggest that anionic salts ameliorated calcium metabolism around parturition by increasing bone resorption and the concentration of ionised calcium in plasma, possibly mediated by a mild hyperchloraemic metabolic acidosis induced by the salts.

Use of pre-partum urine pH to predict the risk of milk fever in dairy cows

The objective of this study was to evaluate the correlation between serum calcium (Ca) and inorganic phosphorus (IP) values and urine pH of cows fed common rations without the addition of anionic salts in late pregnancy. One hundred and seven Holstein cows, having completed two or more lactations and with an expected calving date within the next seven days were selected from two herds. In order to determine levels of serum Ca and IP and urine pH, blood and urine samples were collected seven to one days before parturition. Of the 107 sampled cows, 17 developed recumbency after calving and were considered to be affected by milk fever. There were significant ( p<0.01 ) negative correlations between urine pH and serum Ca, IP and the ratio of Ca to IP, The urine pH, and levels of serum Ca and IP measured within 48 h prior to parturition differed significantly ( p<0.001 ) between recumbent and non-recumbent cows. The sensitivity, specificity, positive and negative predictive values of urine pH test 48 h prior to parturition, using a cut off level of above pH 8.25, were 100%, 81%, 55%, and 100%, respectively. These signify that monitoring urine pH within 48 h prior to parturition is a sensitive method to assess the risk of parturient paresis. The results of this study emphasize the importance of acid-base status of the animal in the pathophysiology of milk fever.

Fractional excretion of electrolytes during pre- and postpartum periods in cows

In this study, fractional excretions (Fe) of sodium (Na), potassium (K), chloride (Cl), calcium (Ca), magnesium (Mg) and phosphorus (PO4) were examined with the aim to demonstrate interactions between fractional excretions of these electrolytes within each period and relate them to electrolyte metabolism in clinically normal cows at different stages of lactation and dry period. The material of this study consisted of 20 clinically healthy Holstein-Friesian cows of the same age and milk yield. Blood and urine samples were collected on 190-200th, 240-250th and 270-280th days of pregnancy and on days 1-7th, 35-45th and 75-85th after calving, altogether 6 times. An increase was observed in FeCa and FeMg during the transition from the lactation to the dry period (p < 0.05), and a decrease in FeCa (p < 0.05), FeMg (p < 0.01) in the 2nd month of the dry period. FePO4 and FeMg, respectively, increased on levels of p < 0.01 and p < 0.05, while FeCa decreased on a level of p < 0.05 after gestation compared to the level before gestation. FeNa and FeK showed a decrease of p < 0.001 and p < 0.01, respectively, between the 1st and 2nd months of the dry period, while after gestation this value showed an increase in FeNa (p < 0.05) and FeK (p < 0.01). FeCl increased significantly (p < 0.05) only from postpartum to the 1st month of lactation. There was a strong positive correlation between FeNa and FeCl in all of the periods. It was concluded that there were significant changes in the Fe of Na, K, Cl, Ca, PO4 and Mg before parturition and during lactation; these changes could have an important role in assessing renal function and electrolyte balance.

Influência da dieta aniônica no balanço macromineral em novilhos holandeses

O efeito do balanço cátion-aniônico da dieta (BCAD) no balanço macromineral (Ca e P), no pH urinário e fecal, na concentração sérica de cálcio ionizado e total e na ingestão de matéria seca foi estudado utilizando-se quatro novilhos holandeses machos. Inicialmente os animais foram alimentados com dieta basal com BCAD de +74,12mEq/kg de MS e, posteriormente, com dieta suplementada com sulfato de amônio, de maneira a diminuir o BCAD para -154,84mEq/kg de MS. Não foram encontradas diferenças (P>0,05) no pH fecal, no balanço de fósforo e na concentração de cálcio ionizado em função do tempo. A urina acidificou-se com a diminuição do BCAD (P<0,01). Para o balanço de cálcio não foram encontradas diferenças entre tratamentos (P>0,05), entretanto, o cálcio excretado na urina foi maior (P<0,05), com a dieta aniônica. A concentração de cálcio total no soro aumentou significativamente (P<0,05) a partir do 19º dia. Dieta aniônica com uso de sulfato de amônio, em veículo palatável, oferecida na forma de ração total, não interferiu na ingestão de matéria seca. O pH urinário é excelente indicativo da eficiência da dieta aniônica e foram necessários 19 dias de consumo de uma dieta aniônica de -154,84 mEq/kg de MS para aumentar os níveis séricos de cálcio total em bovinos em crescimento.

The influence of short-term anion salt exposure on urine pH and on resistance to experimentally induced hypocalcaemia in cows

The objective of this experiment was to induce acidification by anion salt supplementation for 2 days or 10 days and to study the prophylactic effects of such supplementation in preventing hypocalcaemia in cows. It was further attempted to monitor the extent to which any effect on the calcium-regulating mechanisms would persist following a 10-day period of acidification with anion salts. Study animals were three untreated control cows and three cows supplemented with ammonium chloride and ammonium sulphate in their ration for 2 days or 10 days through the rumen cannula. The basic ration of hay was dominated by Urochloa spp. The pH of the urine of the control cows was around 8.00 throughout the experiment and was considered normal. Anion-supplemented cows produced urine with a daily mean pH between 5.5 and 7.0, possibly due to anion salt exposure. The ability to withstand hypocalcaemic challenges was tested by a standardized intravenous infusion of disodium ethylenediaminetetraacetate (Na2EDTA). The calcium regaining time (CRT), expressed as time spent to reach 1.00 mmol/l of ionized calcium during recovery from the EDTA-induced hypocalcaemia, was used to compare cow responses. In the control cows the unexpectedly short CRT, especially during the weekly EDTA tests, could be a result of the repeated induced episodes of hypocalcaemia caused by the EDTA infusions. The improved CRT in the anion-supplemented cows may thus be interpreted as the combined effect of the repeated hypocalcaemic episodes due to EDTA infusions and probably the effect of anion-induced metabolic acidosis on endocrine-regulated calcium homeostatic mechanisms. The effect of anion salt exposure for 10 days on the improvement of calcium-regulating mechanisms was not clear due to the unexpected improvement of CRT that was exhibited by the untreated control cows as well. An on-farm trial of the effect of a 2-day or 10-day anion exposure of dry cows on calcium-regulating mechanisms is suggested.

Milk fever control principles: a review

Three main preventive principles against milk fever were evaluated in this literature review, and the efficacy of each principle was estimated from the results of controlled investigations. Oral calcium drenching around calving apparently has a mean efficacy of 50%-60% in terms of milk fever prevention as well as prevention of milk fever relapse after intravenous treatment with calcium solutions. However, some drenches have been shown to cause lesions in the forestomacs. When using the DCAD (dietary cation-anion difference) principle, feeding rations with a negative DCAD (measured as (Na + K)-(Cl + S)) significantly reduce the milk fever incidence. Calculating the relative risk (RR) of developing milk fever from controlled experiments results in a mean RR between 0.19 and 0.35 when rations with a negative versus positive DCAD are compared. The main drawback from the DCAD principle is a palatability problem. The principle of feeding rations low in calcium is highly efficient in milk fever prevention provided the calcium intake in the dry period is kept below 20 g per day. Calculating the relative risk (RR) of developing milk fever from controlled experiments results in a very low mean RR (between 0 and 0.20) (daily calcium intake below versus above 20 g/d). The main problem in implementing the low-Ca principle is difficulties in formulating rations sufficiently low in calcium when using commonly available feeds. The use of large doses of vitamin D metabolites and analogues for milk fever prevention is controversial. Due to toxicity problems and an almost total lack of recent studies on the subject this principle is not described in detail. A few management related issues were discussed briefly, and the following conclusions were made: It is important to supply the periparturient cow with sufficient magnesium to fulfil its needs, and to prevent the dry cows from being too fat. Available information on the influence of carbohydrate intake, and on the effect of the length of the dry period and prepartum milking, is at present insufficient to include these factors in control programmes.

Plasma calcium, inorganic phosphate and magnesium during hypocalcaemia induced by a standardized EDTA infusion in cows

The intravenous Na2EDTA infusion technique allows effective specific chelation of circulating Ca2+ leading to a progressive hypocalcaemia. Methods previously used were not described in detail and results obtained by monitoring total and free ionic calcium were not comparable due to differences in sampling and analysis. This paper describes a standardized EDTA infusion technique that allowed comparison of the response of calcium, phosphorus and magnesium between 2 groups of experimental cows. The concentration of the Na2EDTA solution was 0.134 mol/l and the flow rate was standardized at 1.2 ml/kg per hour. Involuntary recumbency occurred when ionised calcium dropped to 0.39-0.52 mmol/l due to chelation. An initial fast drop of ionized calcium was observed during the first 20 min of infusion followed by a fluctuation leading to a further drop until recumbency. Pre-infusion [Ca2+] between tests does not correlate with the amount of EDTA required to induce involuntary recumbence. Total calcium concentration measured by atomic absorption remained almost constant during the first 100 min of infusion but declined gradually when the infusion was prolonged. The concentration of inorganic phosphate declined gradually in a fluctuating manner until recumbency. Magnesium concentration remained constant during infusion. Such electrolyte responses during infusion were comparable to those in spontaneous milk fever. The standardized infusion technique might be useful in future experimental studies.

Pathophysiology of calcium and phosphorus disorders

Hypocalcemia and hypophosphatemia are relatively common in periparturient cows. This article reviews the etiologic factors that contribute to the development of these conditions. The physiologic role of magnesium in calcium homeostasis and the physiologic effect of dietary cation-anion difference at the cellular level are discussed in depth. A theory to explain the development of periparturient hypophosphatemia is developed.

Effects of dietary cation-anion difference on the acid-base status of dry cows

Responses in dry matter intake (DMI) and acidbase balance to three sources of anionic salts (dietary cation-anion difference = -63 to -40 meq/kg of dry matter), an acidified fermentation by-product, MgSO4.7H2O + NH4Cl, and MgSO4.7H2O + CaCl2.2H2O + CaSO4, were evaluated relative to the responses of cows fed a control diet (dietary cationanion difference = 203 meq/kg of dry matter) that did not contain anionic salts. Diets were fed for 1-wk periods to eight nonlactating Holsteins assigned to two replicated 4 x 4 Latin squares. Daily DMI increased as time of access to the diet increased up to d 5; mean DMI over d 5 to 7 was reduced by dietary anionic salts. Diets containing anionic salts induced a mild metabolic acidosis that was completely compensated by nonrespiratory mechanisms (decreased blood bicarbonate and base excess; pCO2 and pH values were unaffected). Urinary pH values and bicarbonate excretion were reduced, and urinary NH4+ and titratable acidity excretion were increased, for cows fed diets containing anionic salts. Strong ion difference in urine was decreased by dietary anionic salts because of the relatively greater excretions of Cl- and S2- versus Na+ and K+ by cows fed these diets. Dietary anionic salts decreased mean ruminal pH by 0.12 units, possibly because of the reduced strong ion difference of ruminal fluid. Dietary anionic salts increased mean ruminal NH3 concentration by 2.2 mM, probably because of the higher nonprotein N content of these diets. The strong negative relationship (r2 = 0.95) between urinary pH and net acid excretion by cows fed the diets containing anionic salts suggested that urinary pH measurement might be a useful tool to assess the degree of metabolic acidosis that was imposed by dietary anionic salts.

Effect of anionic salts in prepartum diets based on alfalfa

This study compared prepartum diets based on grass, alfalfa, or alfalfa and anionic salts to investigate their effect on Ca metabolism, acid-base status, endocrine response, disease incidence, and lactational performance of periparturient dairy cows. Forty-five nonlactating Holstein cows in their last 3 wk of gestation were fed a control diet based on grass hay with a dietary cation-anion difference [expressed as milli-equivalents of ((Na + K) - (Cl + S))/100 g of dietary dry matter] of +30 or diets based on alfalfa with a dietary cation-anion difference of either +35 or -7. Cows fed the diet with the dietary cation-anion difference of -7 had the lowest urine pH prepartum and had the highest concentrations of ionized Ca in blood and total Ca in serum at parturition. Increases in 1,25-(OH)2 vitamin D per unit decrease in total Ca in serum were greatest for cows fed the diet with a dietary cation-anion difference of -7. Also, cows fed this same diet consumed the most dry matter postpartum. Incidences of health disorders were 13% (10 of 75), 12% (9 of 75), and 5% (4 of 75) for cows fed the diets with dietary cation-anion differences of +30, +35, and -7, respectively. Results indicate that alfalfa, when supplemented with anionic salts, is a viable forage for prepartum dairy cows.

Dietary cation-anion difference, acid-base status, mineral metabolism, renal function, and milk production of lactating cows

Three switchback experiments were conducted with 12 cows in early lactation, 12 cows in midlactation, and 12 cows in late lactation. Each experiment compared two dietary cation-anion differences. Increasing dietary cation-anion difference increased DMI and milk production in early and midlactation. These effects were not observed in late lactation. Production of milk protein and lactose and concentration of lactose were increased by the higher dietary cation-anion difference in early lactation. Higher dietary cation-anion difference reduced milk fat concentration in midlactation because of the higher milk production. In late lactation, none of the milk components were affected by dietary cation-anion difference. In early and midlactation, apparent absorption of water and urine volume were increased by a higher dietary cation-anion difference; these effects were not caused by higher intake of Na or by higher glomerular filtration rate. Intake, balance, and concentration of S in plasma were increased by the lower cation-anion difference at all stages of lactation. Excretion of HCO3- in urine was reduced by a lower dietary cation-anion difference at all stages of lactation, but secretion of protons in milk was reduced in late lactation only. Increasing dietary cation-anion difference does affect acid-base parameters in urine at all stages of lactation, but DMI and milk production of cows were affected in early and midlactation only.

Acid-base status, renal function, water, and macromineral metabolism of dry cows fed diets differing in cation-anion difference

Dietary cation-anion difference was defined as the summation of the milliequivalents of Na and K minus the sum of the milliequivalents of Cl and S per kilogram of DM. Twelve Holstein cows were used in a crossover experiment to compare the effects of changing the cation-anion difference of a diet based on haylage. Two cation-anion differences, 481.8 and 327.2 meq/kg, were compared. Increased dietary cation-anion difference had no significant effects on BW or intake and digestibility of DM, ADF, NDF, and N. The diet with a cation-anion difference of 481 meq/kg of DM increased apparent absorption of water and urine volume. Fecal excretion of Na and absorption and urinary excretion of S were increased by a cation-anion difference of 327 meq/kg of DM. Although blood concentrations were unaffected, lower dietary cation-anion difference reduced concentrations of H+ and HCO3- in urine and total urinary excretion of HCO3-. Plasma volume, packed cell volume, glomerular filtration rate, and effective renal plasma flow were unaffected by diet. Small changes in dietary cation-anion differences, even within the positive range, affected acid-base status and water metabolism of dry pregnant cows without affecting renal function or blood volume.

Manipulation of dietary cation-anion difference on nutritionally related production diseases, productivity, and metabolic responses of dairy cows

Dietary cation-anion difference has been defined as milliequivalents of (Na+K)-(Cl+S) per kilogram of DM and has a direct impact on blood acid-base metabolism. As this difference decreases, one or more of the following blood parameters change: increased H+, decreased HCO3-, and decreased pH. These changes are accompanied by reduced urinary HCO3- excretion and pH as compensatory mechanisms. Although other minerals have an impact on acid-base metabolism, the four minerals used in dietary cation-anion difference have the greatest effect. Manipulation of acid-base balance can be used to manipulate other biological functions to benefit health and productivity of cows. Low cation-anion difference prepartum can mitigate hypocalcemia peripartum via increased urinary Ca, blood-ionized Ca, and responsiveness to Ca homeostatic hormones. These changes reduced the incidence of paresis and increased productivity by reducing the severity and length of hypocalcemia in all cows (periparturient), regardless of the occurrence of paresis. Reduced cation-anion differences prepartum have been related to a reduced severity of udder edema, likely related to increased renal loss of water and unchanged water intake. However, the effects on acid-base balance cannot be ruled out because of effects on biochemical and transport processes. Elevated cation-anion difference in lactation has been shown to increase DMI and production and to mitigate the effects of heat stress. Because production and heat stress are acidogenic, elevated cation-anion difference improves blood-buffering capacity to cope with H+. In heat stress, elevated water intake with elevated cation-anion difference cannot be ignored. Other diseases related to metabolic acid, such as laminitis and ketoacidosis, may be influenced by elevated cation-anion difference in lactation; however, research in these areas has not been forthcoming.

Effects of diet magnesium on acid-base status and calcium metabolism of dry cows fed acidogenic salts

The objective was to study effects of dietary Mg on acid-base status and Ca metabolism of Holstein cows fed acidogenic diets with relatively high Ca concentrations. Eight nonlactating, nonpregnant Holstein cows were used in a switchback experiment with three 28-d periods. The normal Mg (.2%, dry basis) diet consisted of corn silage plus a concentrate mix supplemented with NH4Cl (126 g/d per cow) and (NH4)2SO4 (126 g/d per cow). The high Mg (.37%, dry basis) diet had MgSO4 substituted for an equivalent amount of S supplied by (NH4)2SO4 in the normal Mg diet. Cation-anion differences of the two diets were -302 (normal Mg) and -289 (high Mg) meq/kg of dietary DM. Compared with cows fed the normal Mg diet, those fed high Mg tended to have higher blood pH and plasma concentrations of total Ca but lower plasma concentrations of P and lower urinary excretion of ammonium and net acid. Cows fed the high Mg diet also tended to increase Mg excretion with a decrease in urinary excretion of Ca. Metabolic responses to intravenous infusion of Na2-EDTA were similar among cows fed either diet. Results indicate that increasing Mg intake of cows fed acidogenic salts was of no advantage with regard to Ca metabolism.