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

Exploring the cause of reduced production responses to feeding corn dried distillers grains in lactating dairy cows

An experiment was conducted to identify the factors that cause reduced production of cows fed a diet with high content of corn distillers grains with solubles (DDGS). We hypothesized that the factors could be high sulfur (S) content in DDGS, which may directly (S toxicity) or indirectly (DCAD) cause reduced production. We also hypothesized that high PUFA in DDGS could be another major factor. In a randomized complete block design, 60 lactating cows (15 primiparous and 45 multiparous; average ± SD at the beginning of the trial: milk yield, 44.0 ± 6.9 kg/d; DIM, 123 ± 50; BW, 672 ± 82 kg) were blocked, and cows in each block were randomly assigned to 1 of the following treatments: SBM (4.7% fatty acids [FA], 0.22% S, and 178 mEq/kg DM of DCAD), a diet containing soybean meal as the main protein source; DG, with SBM replacing mainly soybean byproducts and supplemental fat with distillers grains at 30% dietary DM (4.7% FA, 0.44% S, and 42 mEq/kg DM of DCAD); SBM+S, SBM with sodium bisulfate for additional dietary S (4.8% FA, 0.37% S, and 198 mEq/kg DM of DCAD); SBM+CO, SBM with corn oil (4.7% FA, 0.23%, and 165 mEq/kg DM of DCAD); and DG+DCAD, DG with increased DCAD (4.7% FA, 0.40% S, and 330 mEq/kg DM of DCAD). Due to the limited number of tiestalls, blocks 1 to 6 started the experiment first as phase 1, and the rest of the blocks, as phase 2, started the experiment after phase 1. All cows were fed the SBM diet for 10 d as a covariate period followed by the experimental period for 35 d. Data were analyzed using PROC MIXED of SAS (Version 9.4, SAS Institute Inc.); block and phase were random effects; and treatments, repeated week, and interaction were fixed effects. We found an interaction of week by treatment for DMI. Although milk yield did not change, milk fat concentration tended to decrease (2.78% vs. 3.34%) for DG compared with SBM. Dry matter, OM, NDF, and CP digestibilities were lower when cows were fed the DG diet compared with SBM. Additionally, cows fed DG had lower blood concentrations of HCO3-, base excess, and total (t)CO2 compared with SBM. The SBM+S diet did not affect production, nutrient digestibility, or blood parameters compared with SBM. The SBM+CO diet decreased milk fat concentration and yield compared with SBM. The DG+DCAD diet tended to increase milk fat yield and concentration (1.24 vs. 1.47 kg/d; 2.78% vs. 3.37%) and increased ECM (40.9 vs. 45.1 kg/d) compared with DG but did not improve nutrient digestibility. However, blood HCO3-, base excess, and tCO2 were greater for DG+DCAD compared with DG. In conclusion, the indirect role of S-, altering DCAD, along with the high PUFA content in DDGS, appear to be the factors causing reduced production responses to a high DDGS diet. Increasing DCAD to 300 mEq/kg DM in a high DDGS diet can be a feeding strategy to alleviate reduced production responses.

Effects of Low Dietary Cation and Anion Difference on Blood Gas, Renal Electrolyte, and Acid Excretions in Goats in Tropical Conditions

Goats can suffer from intermittent heat stress in high ambient temperature (HTa) conditions, which causes sporadic respiratory hypocapnia. Obstructive urolithiasis is a common urological problem in goats. Sandy uroliths can be partially relieved by urine acidification with short-term ammonium chloride (NH₄Cl) treatment. However, the outcome of urine acidification and the physiological responses to short-term NH₄Cl supplementation under respiratory hypocapnia of HTa have rarely been reported. The present study investigated the effect of NH₄Cl supplementation that produced a low dietary cation-anion different (l-DCAD) diet on acid-base balance and renal function under HTa conditions. The first experiment investigated the physiological responses to natural HTa to prove whether the peak HTa during the afternoon could induce HTa responses without a change in the plasma cortisol. The partial pressure of CO₂ also tended to decrease during the afternoon. The second experiment examined the short-term effect of l-DCAD under HTa conditions. Although the blood pH was within the normal range, there was a clear acid-base response in the direction of metabolic acidosis. The major responses in renal function were an increase in tubular function and acid excretion. With a comparable level of creatinine clearance, the fractional excretions (FE) of chloride and calcium increased, and the FE of potassium decreased. Acid excretion increased significantly in the l-DCAD group. We conclude that under HTa conditions, the tubular excretion of electrolytes and acids was the major response to acid loading without changing the filtration rate. The l-DCAD formulation can be used to acidify urine effectively.

Metabolic and blood acid-base responses to prepartum dietary cation-anion difference and calcium content in transition dairy cows

Dairy cows commonly undergo negative Ca balance accompanied by hypocalcemia after parturition. A negative dietary cation-anion difference (DCAD) strategy has been used prepartum to improve periparturient Ca homeostasis. Our objective was to determine the influence of a negative DCAD diet with different amounts of dietary Ca on the blood acid-base balance, blood gases, and metabolic adaptation to lactation. Multiparous Holstein cows (n = 81) were blocked into 1 of 3 dietary treatments from 252 d of gestation until parturition: (1) positive DCAD diet and low Ca (CON; containing +6.0 mEq/100 g DM, 0.4% DM Ca); (2) negative DCAD diet and low Ca (ND; -24.0 mEq/100 g DM, 0.4% DM Ca); or (3) negative DCAD diet plus high Ca supplementation (NDCA; -24.1 mEq/100 g DM, 2.0% DM Ca). There were 28, 27, and 26 cows for CON, ND, and NDCA, respectively. Whole blood was sampled at 0, 24, 48, and 96 h after calving for immediate determination of blood acid-base status and blood gases. Serum samples collected at -21, -14, -7, -4, -2, -1, at calving, 1, 2, 4, 7, 14, 21, and 28 d relative to parturition were analyzed for metabolic components. Results indicated that cows fed ND or NDCA had lower blood pH at calving but greater pH at 24 h after calving compared with CON. Blood bicarbonate, base excess, and total CO₂ (tCO₂) concentrations of cows in ND and NDCA groups were less than those of cows in CON at calving but became greater from 24 to 96 h postpartum. The NDCA cows had lower blood bicarbonate, base excess, and tCO₂ at 48 h and greater partial pressure of oxygen after calving compared with ND. Cows fed ND or NDCA diets had lower serum glucose concentrations than CON cows before calving but no differences were observed postpartum. Serum concentrations of total protein and albumin were greater prepartum for cows in ND and NDCA groups than for those in CON. Postpartum serum urea N and albumin concentrations tended to be higher for ND and NDCA cows. Cows fed ND or NDCA diets had elevated serum total cholesterol concentration prepartum. During the postpartum period, triglycerides and NEFA of cows fed ND or NDCA diets tended to be lower than those of CON. Cows fed the NDCA diet had greater postpartum total cholesterol in serum and lower NEFA concentration at calving than ND. In conclusion, feeding a prepartum negative DCAD diet altered blood acid-base balance and induced metabolic acidosis at calving, and improved protein and lipid metabolism. Supplementation of high Ca in the negative DCAD diet prepartum was more favorable to metabolic adaptation to lactation in dairy cows than the negative DCAD diet with low Ca.

Short communication: Characterization of molasses chemical composition

Beet and cane molasses are produced worldwide as a by-product of sugar extraction and are widely used in animal nutrition. Due to their composition, they are fed to ruminants as an energy source. However, molasses has not been properly characterized in the literature; its description has been limited to the type (sugarcane or beet) or to the amount of dry matter (DM), total or water-soluble sugars, crude protein, and ash. Our objective was to better characterize the composition of cane and beet molasses, examine possible differences, and obtain a proper definition of such feeds. For this purpose, 16 cane and 16 beet molasses samples were sourced worldwide and analyzed for chemical composition. The chemical analysis used in this trial characterized 97.4 and 98.3% of the compounds in the DM of cane and beet molasses, respectively. Cane molasses contained less DM compared with beet molasses (76.8 ± 1.02 vs. 78.3 ± 1.61%) as well as crude protein content (6.7 ± 1.8 vs. 13.5 ± 1.4% of DM), with a minimum value of 2.2% of DM in cane molasses and a maximum of 15.6% of DM in beet molasses. The amount of sucrose differed between beet and cane molasses (60.9 ± 4.4 vs. 48.8 ± 6.4% of DM), but variability was high even within cane molasses (39.2-67.3% of DM) and beet molasses. Glucose and fructose were detected in cane molasses (5.3 ± 2.7 and 8.1 ± 2.8% of DM, respectively), showing high variability. Organic acid composition differed as well. Lactic acid was more concentrated in cane molasses than in beet molasses (6.1 ± 2.8 vs. 4.5 ± 1.8% of DM), varying from 1.6 to 12.8% of DM in cane molasses. Dietary cation-anion difference showed numerical differences among cane and beet molasses (7 ± 53 vs. 66 ± 45 mEq/100 g of DM, on average). It varied from -76 to +155 mEq/100 g of DM in the cane group and from +0 to +162 mEq/100 g of DM in the beet group. Data obtained in this study detailed differences in composition between sources of molasses and suggested that a more complete characterization could improve the use of molasses in ration formulation.

The effect of dietary ions difference on drinking and eating patterns in dairy goats under high ambient temperature

OBJECTIVE

The present study was carried out to evaluate the effect of high dietary cation and anion difference (DCAD) rations on diurnal variations in eating and meal patterns, water intake and urination patterns in dairy goats fed under high ambient temperature (HTa).

METHODS

Ten crossbred dairy goats during peri-parturition period were selected and divided into two groups of five animals each. Experimental diets were control DCAD (control, 22.8 mEq/100 g dry matter [DM]) and high DCAD (DCAD, 39.1 mEq/100 g DM). The composition of two diets consisted of 44% corn silage and 56% concentrate. From the 2nd week to 8th week postpartum, goats were fed ad libitum twice daily either with the control or DCAD total mix ration with free access to water. The spontaneous eating and drinking patterns were determined.

RESULTS

The environmental conditions in the present experiment indicated that goats were fed under HTa conditions (average peak THI = 85.2) and were in heat stress. In addition to the typical HTa induced tachypnoea in both groups, the respiratory rate in the DCAD group was significantly higher than the control group (p<0.05). Although the goats from both groups showed comparable level of eating, drinking and urination during experiment, the meal pattern and water intake were different. High DCAD apparently increased eating and meal patterns compared with the control. At week 8 postpartum, goats from high DCAD group had significant (p<0.05) bigger meal size and longer meal duration. Moreover, high DCAD appeared to increase night-time water intake (p<0.05).

CONCLUSION

Both meal pattern and night-time drinking effects of DCAD suggested that feeding with high DCAD ration may alleviate the effect of heat stress in dairy goat fed under HTa conditions.

Reducing prepartum urine pH by supplementing anionic feed ingredients: Effects on physiological and productive responses of Holstein × Gir cows

This study compared physiological and productive parameters in 3/4 Holstein × 1/4 Gir dairy cows receiving a prepartum concentrate containing ammonium chloride to reduce urine pH near 7.0 (CON; n = 17), or a commercial anionic supplement to reduce urine pH near 6.0 (SUPP; n = 17). Nonlactating, multiparous, pregnant cows were assigned to receive SUPP or CON beginning 21 d before expected date of calving. Cows were maintained in a single drylot pen with ad libitum access to corn silage, and individually received their prepartum concentrate once daily (0800 h) before calving. Cows from both treatments completely consumed their concentrate allocation within 30 min after feeding. Cow body weight and body condition score were recorded once weekly, urine pH measured every 3 d, and blood samples collected on d -21, -14, -9, -6, and -3 relative to expected calving date. After calving (d 0), cows were moved to an adjacent drylot pen with ad libitum access to water and a total mixed ration, and were milked twice daily (0600 and 1700 h). Cow body weight and body condition score were recorded once weekly and individual milk production was recorded daily until 30 d in milk (DIM). Blood samples were collected before each milking during the first 5 DIM, as well as at 6, 9, 16, 23, and 30 DIM before the morning milking. Based on actual calving dates, cows received SUPP or CON for (mean ± standard error) 19.2 ± 1.2 and 19.0 ± 0.9 d before calving, respectively. Urine pH was less in SUPP versus CON cows during the last 15 d of gestation (6.12 vs. 7.15, respectively). Milk yield during the first 5 DIM and throughout the experimental period was greater in SUPP versus CON cows (by 20 and 14%, respectively), whereas serum Ca concentrations did not differ between treatments during the first 5 DIM. Serum concentrations of fatty acids were greater in SUPP versus CON cows 3 d before and at calving (by 52 and 22%, respectively), whereas SUPP cows had lower serum glucose and cortisol concentration at calving (by 23 and 27%, respectively). Hence, the SUPP treatment decreased prepartum urine pH near 6.0 in Holstein × Gir dairy cows without depressing concentrate intake compared with CON, although total dry matter intake was not evaluated to fully investigate feed intake responses. Moreover, the SUPP treatment transiently affected serum glucose, fatty acids, and cortisol concentrations near the time of calving, and resulted in greater milk yield during the initial 30 DIM compared with CON.

A 100-Year Review: From ascorbic acid to zinc-Mineral and vitamin nutrition of dairy cows

Mineral and vitamin nutrition of dairy cows was studied before the first volume of the Journal of Dairy Science was published and is still actively researched today. The initial studies on mineral nutrition of dairy cows were simple balance experiments (although the methods available at the time for measuring minerals were anything but simple). Output of Ca and P in feces, urine, and milk was subtracted from intake of Ca and P, and if values were negative it was often assumed that cows were lacking in the particular mineral. As analytical methods improved, more minerals were found to be required by dairy cows, and blood and tissue concentrations became primary response variables. Those measures often were poorly related to cow health, leading to the use of disease prevalence and immune function as a measure of mineral adequacy. As data were generated, mineral requirements became more accurate and included more sources of variation. In addition to milk yield and body weight inputs, bioavailability coefficients of minerals from different sources are used to formulate diets that can meet the needs of the cow without excessive excretion of minerals in manure, which negatively affects the environment. Milk, or more accurately the lack of milk in human diets, was central to the discovery of vitamins, but research into vitamin nutrition of cows developed slowly. For many decades bioassays were the only available method for measuring vitamin concentrations, which greatly limited research. The history of vitamin nutrition mirrors that of mineral nutrition. Among the first experiments conducted on vitamin nutrition of cows were those examining the factors affecting vitamin concentrations of milk. This was followed by determining the amount of vitamins needed to prevent deficiency diseases, which evolved into research to determine the amount of vitamins required to promote overall good health. The majority of research was conducted on vitamins A, D, and E because these vitamins have a dietary requirement, and clinical and marginal deficiencies became common as diets for cows changed from pasture and full exposure to the sun to stored forage and limited sun exposure. As researchers learned new functions of fat-soluble vitamins, requirements generally increased over time. Diets generally contain substantial amounts of B vitamins, and rumen bacteria can synthesize large quantities of many B vitamins; hence, research on water-soluble vitamins lagged behind. We now know that supplementation of specific water-soluble vitamins can enhance cow health and increase milk production in certain situations. Additional research is needed to define specific requirements for many water-soluble vitamins. Both mineral and vitamin research is hampered by the lack of sensitive biomarkers of status, but advanced molecular techniques may provide measures that respond to altered supply of minerals and vitamins and that are related to health or productive responses of the cow. The overall importance of proper mineral and vitamin nutrition is known, but as we discover new and more diverse functions, better supplementation strategies should lead to even better cow health and higher production.

Can neutral dietary cation-anion difference (DCAD) decrease occurrence of clinical periparturient hypocalcaemia in dairy cattle?

BACKGROUND

Adjusting the dietary cation-anion difference (DCAD) is one of the most efficient ways to stimulate calcium homeostasis in periparturient dairy cattle. However, adjusting DCAD to the recommended negative values (-100 to -150 mEq/kg) is associated with decreased food intake and metabolic acidosis. The critical conditions of the animals at peripartum (i.e. drastic hormonal changes, decreased appetite and negative energy balance) can be detrimental to the health, productivity and welfare of the animals if combined with decreased feed intake caused by unpalatable acidogenic salts.

METHODS

In a cross-sectional study, we analysed the ration of eight small to large dairy herds with intensive husbandry systems, including 6949 dry cows. Sodium, potassium, chlorine and sulfur concentrations in the feed were determined and DCAD was calculated. The DCAD of the ration of the farms ranged from -33.5 to +24.7 mEq/kg. Parturient paresis (PP, or milk fever) prevalence was investigated and correlated to DCAD values.

RESULTS

Clinical PP occurrence in the dairies of this investigation on average declined by 87% (ranging from a 97% decline to 5% increase). This indicates that adjusting DCAD at neutral values (0 ± 30 mEq/kg range) may both lower the PP prevalence and increase ration palatability by lowering acidogenic salts in the ration.

CONCLUSIONS

Further research is recommended to investigate the effects of neutral DCAD on subclinical hypocalcaemia and food intake of the cattle.

Effect of negative dietary cation-anion differences on carcass characteristics and beef tenderness of Japanese Black steers

Lowering dietary cation-anion differences (DCAD) can enhance responsiveness to Ca-homeostatic hormones and increase Ca availability, which might have potential to activate a Ca-dependent protease, calpain, and to enhance postmortem myofibrillar proteolysis. In this study, we investigated the effects of DCAD manipulation on calpain activity and beef tenderness in Japanese Black cattle which are characterized by their high marbling. Thirty-six Japanese Black steers were allotted to one of two treatments: (i) control (CON; DCAD +6.09 mEq/100 g of dry matter (DM)) or (ii) negative DCAD (NEGD; DCAD -8.27 mEq/100 g DM) for 70 days before slaughter. Lowering DCAD decreased DM and energy intake (P < 0.01) even though it did not negatively affect the growth performance or carcass characteristics. In NEGD, urine pH was decreased by acidification caused by the negative DCAD (P < 0.01). Calpain activities tended to be improved in NEGD (P = 0.09), but Warner-Bratzler shear force values were not affected by treatment. Although calpain activities tended to improve, lowering DCAD to -8.27 for 70 days before slaughter was insufficient to enhance beef tenderness in Japanese Black steers.

A Dairy Herd Case Investigation with Very Low Dietary Cation-Anion Difference in Prepartum Dairy Cows

During the periparturient period, subclinical hypocalcemia (total plasma Ca concentration <2.0 mmol/l) is a potential problem for the dairy cow; consequently, its prevention is essential for success of fertility and productive performance. Dietary cation–anion difference (DCAD) has been defined as the difference in milliequivalents of cations (Na, K) and anions (Cl, S) per kilogram of dry matter (DM) and has a direct impact on blood acid–base metabolism. Diets rich in K and Na induce metabolic alkalosis, interfering with tissue sensitivity to parathyroid hormone, and diets rich in Cl and S (anionic salts) cause metabolic acidosis, reducing the risk of hypocalcemia. Consequently, the use of anionic salts has become a popular method to prevent hypocalcemia in dairy cattle. Monitoring diets with anionic salts can be done by measuring urine pH, with optimal values between 6.2 and 6.8 for Holstein cows. The objective of this report is to present a herd case investigation involving a dairy farm feeding a very low DCAD (−143 mEq/kg DM), expecting improved Ca homeostasis. The diet of −143 mEq/kg (urine pH 5.2–5.8) was changed to a diet with −53 mEq/kg DM (urine pH 6.2–6.8). Blood samples were taken at the time of calving for 10 cows that calved before and then for 10 cows that calved after changing the diet. Cows with extremely low DCAD had Ca concentrations of 2.11 ± 0.22 mmol/l and cows with a more moderated DCAD, 2.11 ± 0.16 mmol/l (P > 0.05). Several other blood metabolites (P, Mg, Na, K, Cl, albumin, globulins, blood urea nitrogen, creatinine, and GGT) were also similar between groups. This very low DCAD during the prepartum period may severely compromise animal physiology unnecessarily, with little advantage over normal calcium concentrations at parturition, when compared with a less negative DCAD (−53 mEq/kg DM). Feeding a less negative DCAD ration (−53 mEq/kg DM) did not decrease plasma Ca levels right after parturition compared to a DCAD ration of −143 mEq/kg DM, reinforcing the lack of benefit of a more negative DCAD.

Acidogenic mineral additions increased Ca mobilization in prepartum sows

Increased sow milk production is associated with an increase in unexplained sow mortality during prepartum and early postpartum periods. This association has led to purported claims of hypocalcemic disorders. Assuming similar responses as dairy cows, feeding anionic mineral salts in late gestation and early lactation may reduce potential hypocalcemia related disorders in sows. Two experiments using CAD-MATE (Granco Minerals, Petersburg, VA), an acidogenic mineral supplement (AMS), were designed to determine the amount required to increase urinary Ca excretion and to identify renal compensatory responses to acid loads in sows. In Exp. 1, 30 multiparous gestating sows (Landrace × Large White) were fed 1 of 6 diets with either 0, 0.5, 1.0, 1.5, 2.0, or 2.5% AMS additions for 14 d. Diets provided a range (33 to -216 mEq/kg) of cation-anion balance, calculated as Na + K - Cl - S. Two 24-h urine samples were collected via bladder catheters for mineral analysis. One venous blood sample was drawn from 2 sows per diet on d 14. In Exp. 2, twelve sows were fed 1 of 3 diets to provide either 0, 1.5, or 2.5% AMS. Three 24-h composites of urine and fecal excreta were collected and analyses were used to calculate apparent mineral retention. Venous blood pH (range 7.41 to 7.33) and base excess (range 5.4 to 0.5 mmol/L) decreased (linear, < 0.10), but blood ionized Ca (range 1.28 to 1.37 mmol/L) increased (linear, < 0.05) proportionally to dietary AMS additions. Blood anion gap was not affected by diet. Urine pH decreased (linear, < 0.10) with additions of AMS (range 7.47 to 5.52). In Exp. 2, urinary SO (range 134 to 396 mEq/d) and NH (range 84 to 323 mEq/d) excretion increased ( < 0.05) with AMS additions. Urinary Mg, Na, and K excretion did not differ among treatments. Fecal excretion of Ca, Mg, and P increased ( < 0.05) in sows fed diets with 2.5% AMS. Fecal K, Na, and Cl excretion did not differ among treatments. Apparent Ca retention decreased ( < 0.05) with AMS additions, but apparent Mg and Cl retention increased ( < 0.05). In conclusion, AMS induced a renal compensated acid load as exhibited by urinary ion excretion patterns and maintenance of blood gas values within physiological ranges. Feeding diets with 1.5 or 2.5% AMS increased urinary and fecal Ca excretion and decreased apparent Ca retention implying an increase in mobilization of body Ca pools in prepartum sows.

Effect of dietary potassium supplementation on the calcium absorption capacity in the rumen and abomasum and fractional excretion of urinary minerals in sheep

The aim of this study was to determine the effect of potassium (K) supplementation on the calcium (Ca) absorption capacity from the rumen and abomasum of sheep. The Ca absorption capacity from the rumen and abomasum of sheep was measured using stable strontium (Sr) as a Ca-analogue tracer method. The sheep, cannulated at either the rumen or abomasum, were randomly allocated to one of two groups (control or K-supplemented) and fed in individual metabolism pens twice daily with a diet comprising oaten hay, lucerne chaff and barley fortified with or without potassium carbonate (K2CO3). The K content of the diet of the K-supplemented animals was 3.1% of dry matter compared with 1.4% for the control animals. The animals were fed their respective diets for a period of 2 weeks. The fractional absorption capacity (FC) of Ca was estimated before, during and after the treatment period. Supplementation with K decreased the FC of Ca in both the rumen and abomasum during treatment and increased the FC of Ca in the abomasum post-treatment. Supplementation with K also increased the fractional excretion of K in the urine, but decreased the fractional excretion of Ca and magnesium (Mg) (P < 0.05), showing that K supplementation significantly affected Ca and Mg metabolism. Results suggest that renal conservation of Ca and Mg is an important mechanism controlling the Ca and Mg pool for vital functions of the body. In times of high demand for these minerals during lactation and pregnancy, high K in the diets may predispose sheep to hypomagnesaemia and hypocalcaemia, which in turn will have a negative impact on productivity and economic returns.

Effect of decreasing dietary cation anion difference on feedlot performance, carcass characteristics, and beef tenderness

The manipulation of acid-base balance has been extensively investigated as a means of manipulating Ca homeostasis and managing milk fever in dairy cows. A low dietary cation anion difference (DCAD) increases urinary Ca, blood-ionized Ca, and responsiveness to Ca-homeostatic hormones. Very little attention has been focused on the possibility of using a low dietary DCAD to increase muscle Ca availability, calpain activity, and meat tenderness of beef cattle. Thus, 90 Angus × Simmental crossbred steers were allotted by weight (590.1 ± 2.4 kg) and breed composition (% Simmental) to 3 treatments (6 pens/treatment, 5 steers/pen) to evaluate the effects of DCAD on beef tenderness. Treatments were initiated 2 wk before slaughter and consisted of 3 DCAD (mEq/100 g) treatments: -16, 0, and +16. Basal diets (DM basis) were 62 to 64% corn, 6 to 9% soybean meal, and 20% corn silage, and were formulated to contain similar concentrations of protein, energy (NEm; NEg), and minerals, with the exception of sodium and chlorine. A commercial chloride ion supplement (PASTURChlor, West Central, Ralston, IA) was added to diets to decrease DCAD and sodium bicarbonate was added to diets to increase DCAD. Performance before initiation of the study did not differ among treatments (P > 0.22). Urine pH did not differ at the initiation of the study (P > 0.57), but did increase at a decreasing rate on d 7 (6.37, 7.69, 8.13) and d 14 (5.68, 7.66, 8.03) of the study as DCAD increased from -16 to 0 to +16, respectively (quadratic, P < 0.02). Gain and gain:feed responded quadratically to DCAD (P < 0.01), increasing from -16 to 0 DCAD and decreasing from 0 to +16 DCAD. Hot carcass weight, dressing percent, fat thickness, LM area, yield grade, marbling score, quality grade distribution, 48 h muscle pH, and Ca content of muscle did not differ among treatments (P > 0.16). In addition, DCAD did not affect Warner-Bratzler shear force among treatments after 7 and 21 d of aging (P > 0.23). Although urine pH was decreased by feeding a -16 DCAD diet, Ca influx into the LM and beef tenderness were not affected by altering the DCAD in finishing beef cattle diets.

Anionic salts and dietary 25-hydroxyvitamin D stimulate calcium availability in steers

The influence of feeds containing varying dietary cation-anion differences (DCADs) with and without supplements of 25-hydroxyvitamin D (25(OH)D) on urine pH and excretion of macro minerals was determined in fistulated crossbred steers (mean live weight 315 ± 45 kg). A basal forage diet comprising lucerne hay and wheat chaff was used, to which varying quantities of MgCl(2) or K(2)CO(3) were added to achieve four levels of DCAD: -300, 50, 150 or 250 mEq/kg dry matter (DM). Steers were allocated to one of six treatments, one treatment for each diet and a further treatment for both the 50 and 150 mEq/kg DCAD diets, which were supplemented with 25(OH)D at a rate of 3 mg/steer per day. Urine pH from steers offered the diets comprising DCADs of 50, 150 and 250 mEq/kg ranging from 8.3 to 8.8. In treatments not containing 25(OH)D with DCADs of 50 to 250 mEq/kg, there were no significant differences in urine pH or Ca excretion. However, steers offered the diet with a DCAD of -300 mEq/kg DM produced urine with a significantly lower pH (6.5 to 7.5). Daily output of Ca in urine was also significantly higher from steers given this diet. Supplementation with 25(OH)D significantly increased urinary Ca excretion from steers offered diets of DCADs 50 and 150 mEq/kg DM. Estimates of daily urinary Ca excretion, calculated using the ratio of creatinine to Ca in 'spot' urine samples, were less variable than those based on total collection (residual mean square of 0.54 and 0.63, respectively).

Influence of varying levels of dietary cation anion difference on ruminal characteristics, nitrogen metabolism and in situ digestion kinetics in buffalo bulls

This study was conducted to examine the influence of varying dietary cation anion difference (DCAD) on nutrient intake, digestibility, ruminal characteristics, blood acid base status and in situ digestion kinetics in Nili Ravi buffalo bulls. Four iso-nitrogenous and iso-caloric diets having -110, +110, +220 and +330 mEq/kg dry matter (DM) DCAD were formulated which were represented by A (anionic), LC (low cationic), MC (medium cationic) and HC (high cationic), respectively. These diets were used in four ruminally cannulated Nili Ravi buffalo bulls in a 4 × 4 Latin Square Design. Improved nutrient intake was recorded at high DCAD levels while digestibility remained unaffected. Ruminal ammonia nitrogen, rumen pH, acetate and acetate : propionate ratio were higher in buffalo bulls fed MC and HC diets than those fed A and LC diets. Blood pH and HCO₃⁻ also tended to increase as DCAD level was increased in the diet. Serum Ca and Cl concentrations were higher in bulls fed A and LC diets whereas serum Mg, P and S remained unaffected. Urine pH increased with increasing DCAD level. Nitrogen intake and blood urea nitrogen concentrations were also higher in bulls fed MC and HC diets. There was a consistent increase in ruminal DM and neutral detergent fiber degradability, rate of disappearance and extent of digestion at high DCAD levels in the diet. However, lag time decreased at high DCAD level. This study indicated that buffalo bulls fed MC and HC diets improved feed intake, ruminal characteristics and digestion kinetics.

Resposta em parâmetros sanguíneos e urinários de vacas leiteiras ao aumento no balanço cátion-aniônico da dieta

Estudou-se efeito de quatro níveis de dietas catiônicas sobre os parâmetros ácido-base do sangue e o pH urinário de vacas em lactação. Para a manipulação dos níveis do balanço cátion-amônico da dieta (BCAD), foram adicionadas diferentes concentrações de bicarbonato de sódio às dietas, obtendo-se os seguintes tratamentos: +150, +250, +400 e +500mEq/kg de matéria seca. O experimento foi realizado durante o verão, por um período total de 72 dias, utilizando-se oito vacas da raça Holandesa após o pico de lactação, distribuídas em quadrado latino (4x4), replicado, em que cada período teve duração de 18 dias. O pH urinário e o bicarbonato, o pH, o CO2 total e a pCO2 do sangue aumentaram linearmente (P<0,01) com o aumento do BCAD. As concentrações de sódio e potássio do sangue não foram modificadas (P>0,05) pelo BCAD. A concentração de cloro no sangue diminuiu linearmente (P<0,01) com o aumento do BCAD. O aumento do BCAD afetou o equilíbrio ácido-base das vacas, promovendo efeito alcalinogênico, o que poderia levar a diferenças significativas no desempenho do animal.

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.

Effects of dietary strong acid anion challenge on regulation of acid-base balance in sheep1

The acid-base status of the extracellular fluid is directly affected by the concentrations of strong basic cations and strong acid anions that are absorbed into the bloodstream from the diet. The objective of this study was to develop and characterize a model for dietary acid challenge in sheep by decreasing the dietary cation-anion difference (DCAD) using NutriChlor (HCl-treated canola meal), an anionic feed supplement. Ten fully fleeced sheep (Rideau-Arcott, 54.3 +/- 6.7 kg of BW) were fed either a control supplement [200 g/d of canola meal, DCAD = 184 mEq/kg of DM, calculated as (Na+ + K+) - (Cl- + S2-)] or an anionic supplement (AS; 200 g/d of NutriChlor, DCAD = -206 mEq/kg of DM) offered twice daily at 0700 and 1100 in a randomized complete block design. The sheep were individually housed and limit-fed a basal diet of dehydrated alfalfa pellets (22% CP and 1.2 Mcal of NE(g)/kg, DM basis) at 1.1 kg of DM/d offered twice daily at 1000 and 1300. Two days before the beginning of the experiment, the sheep were fitted with vinyl catheters (0.86-mm i.d., 1.32-mm o.d.) in the left jugular vein to facilitate blood sampling. Blood and urine samples were obtained daily from 1100 to 1130 on d 1 through 9 and at 0700, 1000, 1300, 1600, and 1900 on d 10. Blood was analyzed for hematocrit, plasma pH, gases, strong ions, and total protein. Urine samples were analyzed for pH. The AS induced a nonrespiratory acid-base disturbance associated with lower (P < 0.05) plasma pH (7.47 vs. 7.39), lower (P < 0.05) urine pH (8.13 vs. 6.09), and lower (P < 0.05) strong ion difference (42.5 vs. 39.5). The AS reduced (P < 0.05) the concentration of plasma glucose, base excess, and bicarbonate and increased (P < 0.05) the concentration of K+ and Cl-. Lowering DCAD increased (P < 0.05) Ca2+ concentrations in plasma by 13%. In conclusion, this dietary model successfully induced a significant acid-base disturbance in sheep. Although the acidifying effects of negative DCAD in the diet may have short-term prophylactic effects of elevating the concentration of Ca2+ in plasma, negative DCAD may have detrimental effects on acid-base balance.

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.

Effects of Dietary Cation-Anion Difference and Potassium to Sodium Ratio on Lactating Dairy Cows in Hot Weather

Forty-two lactating Holstein cows 188 +/- 59 d in milk were used in an 8-wk randomized complete block trial with a 2 x 3 factorial arrangement of treatments. The objective was to determine the effects of high dietary cation-anion difference (DCAD) and K:Na ratio on milk yield and composition and blood acid-base chemistry. Treatments included DCAD concentrations of 45 or 60 mEq (Na + K -Cl)/100 g of feed dry matter and K:Na ratios of 2:1, 3:1, or 4:1. Mean DCAD values were later determined to be 41 and 58. Dry matter intake was similar across treatments. Yield of milk and energy corrected milk were lower for the 3:1 K:Na ratio compared with 2:1 and 4:1 ratios. Blood urea N was lower for the highest DCAD, suggesting that DCAD possibly reduced protein degradation or altered protein metabolism and retention. Mean temperature-humidity index was 75.6 for the duration of the trial, exceeding the critical value of 72 for all weeks during the treatment period. Cows maintained relatively normal body temperature with mean a.m. and p.m. body temperature of 38.5 and 38.7 degrees C, respectively. These body temperatures suggest that cows were not subject to extreme heat stress due to good environmental control. Results of this trial indicate that the greatest effect on milk yield occurs when either Na or K is primarily used to increase DCAD, with the lowest yield of energy-corrected milk at a 3:1 K:Na ratio (27.1 kg/d) compared with ratios of 2:1 (29.3 kg/d) and 4:1 (28.7 kg/d). Results also suggest that greater DCAD improves ruminal N metabolism or N utilization may be more efficient with a high DCAD.

The effect of formulation and amount of potassium fertilizer on macromineral concentration and cation-anion difference in tall fescue

This study investigated the feasibility of altering the dietary cation-anion difference (DCAD) in grass by altering the grass variety and the amount and formulation of K fertilizer application. In experiment 1, treatments were combinations of 2 varieties (Barcel and Hi-Mag) of tall fescue (Festuca arundinacea Schreb); 2 rates of K (0 and 250 kg/ha), supplied as KCl; and 2 rates of Mg (0 and 60 kg/ha), supplied as MgO. In experiment 2, K fertilizer was applied at 0 or 125 kg/ha as KCl or K2SO4. There was no difference between HiMag and Barcel tall fescue in the concentrations of Mg, S, and Cl. Application of K fertilizer decreased concentrations of Mg, but the magnitude of the decrease was not consistent across harvests. Conversely, application of Mg fertilizer increased Mg concentrations, but again, the magnitude of the increase was not consistent across harvests. The concentrations of Ca were higher in HiMag than in Barcel tall fescue, with the magnitude of the difference increasing from first to last harvest. Potassium fertilizer decreased Ca concentrations in the first, fourth, and fifth harvests only. Calcium concentration was decreased by a greater magnitude in HiMag tall fescue as a result of Mg fertilization. The HiMag tall fescue contained lower concentrations of K than did Barcel tall fescue in the first, second, and third harvests. Application of K fertilizer increased the K concentration in all 5 harvests but did not affect Na concentrations except in the last harvest. The HiMag tall fescue contained less Na than did Barcel, but the magnitude of the difference was affected by K and Mg fertilization. Application of K fertilizer decreased S concentrations in first-harvest grass, increased concentrations in second-and third-harvest grasses, and had no effect in fourth-or fifth-harvest grasses. Application of Mg fertilizer decreased S concentrations of tall fescue. Application of K fertilizer increased DCAD values for grass harvested from the second through fifth harvests. The increase in DCAD attributable to K fertilizer was less in HiMag than in Barcel tall fescue. Application of K fertilizer as K2SO4 increased dry matter yield and S concentrations of HiMag tall fescue, whereas K applied as KCl increased concentrations of K and Cl. There was no effect of fertilizer formulation on Na concentrations. The DCAD was lower in HiMag tall fescue fertilized with K2SO4 compared with that fertilized with KCl. This study showed that DCAD of grass can be manipulated by the choice of grass variety, fertilizer formulation, and fertilizer application rate.

Experimental studies on the impact of an increased dose of anionic salts on the metabolism of dairy cows

This study was initiated to investigate the influence of a daily dose of anionic salts (AS) above the valid upper limit at present on metabolism of dairy cows. Eleven non-pregnant and non-lactating Holstein-Friesian crossbred cows with a permanent rumen cannula were used in a study with a controlled feeding design. The initial daily dose was 2500 meq/day, which resulted in a Dietary Cation Anion Difference (DCAD) of -211 meq/kg dry matter. Every seven days,the daily dose was raised by 500 meq. If a cow stopped eating, the application of AS was stopped and these cows were monitored over the next seven days. On day 30 another batch of hay, having the same DCAD but higher concentrations of minerals and energy, was fed. Blood and urine samples were taken to monitor acid-base balance and calcium concentrations. Acid-base balance was strongly influenced by AS. Blood pH dropped steadily and reached values around 7.23. Urine pH dropped quickly below 6 and remained at that level regardless of the increased dosage of AS. Net acid base excretion (NABE) fell continuously with the increase of the dosage of AS and reached values below -200 mmol/l. Calcium concentrations in the serum were nearly stable, but those in urine increased sharply and remained on an elevated level with increasing doses of AS. A few days before the individual cow's refusal of feed intake, calcium excretion in urine decreased. The majority of cows stopped eating while consuming a diet containing 3500 to 4000 meq AS except two animals who consumed up to 6000 meq/day AS but they received the better hay in the second half of the treatment period. In this time pH in blood increased slowly. NABE remained stable on a low level at -100 mmol/l. The results showed that with an increasing amount of AS fed the risk of clinical acidosis increased. The decreasing urine concentrations of calcium indicate a breakdown of the compensation capability of the single cow. Besides the dose of AS fed, the quality of the feed stuff might be another factor concerning the tolerance of cows against AS.

Effects of 25-hydroxyvitamin D3 and manipulated dietary cation-anion difference on the tenderness of beef from cull native Korean cows

In this study, we characterized the effects of 25-hydroxyvitamin D3 (25-OH D3) and manipulated dietary cation-anion difference (DCAD) on the performance, urine pH, serum constituents, carcass traits, tissue residual vitamin D and its metabolites, beef tenderness, and mRNA and protein concentrations of Ca-dependent proteinases in LM using 24 cull native Korean cows. The cows were divided into 3 groups of 8: control, 25-OH D3 supplemented (25-OH D3), and manipulated DCAD plus 25-OH D3 supplemented (DCAD+25-OH D3). Cows receiving 25-OH D3 or DCAD+25-OH D3 were dosed with 125 mg of 25-OH D3 6 d before slaughter. The manipulated DCAD (-10 mEq/100 g of DM) diet was fed from 20 to 6 d (14 d) before slaughter. The DCAD+25-OH D3 treatment decreased urine pH and increased serum Ca concentrations. Although the vitamin D concentrations in LM, liver, and kidney were not affected by 25-OH D3 or DCAD+25-OH D3, muscle tissue 25-OH D3 concentrations were increased by both regimens. Serum 25-OH D3 concentrations were increased by 25-OH D3 supplementation, and the increase was even greater for DCAD+25-OH D3. The same pattern was observed for serum 1,25- (OH)2 D3. However, the LM concentration of 1,25-(OH)2 D3 was less for DCAD+25-OH D3 than for control. Although Ca concentrations of LM increased numerically in response to 25-OH D3 supplementation, no statistical differences in Warner-Bratzler shear force or sensory traits of LM were detected. The LM of cows receiving 25-OH D3 with or without manipulated DCAD had greater concentrations of mu-calpain and m-calpain mRNA, whereas the reverse was observed for calpastatin mRNA. Expression of mu-calpain protein was increased relative to control by DCAD+25-OH D3. The amount of 25-OH D3 and manipulated DCAD administered to cull native Korean cows was insufficient to improve tenderness of beef by increasing muscle Ca concentration. However, DCAD+25-OH D3 induced greater expressions of mu-calpain protein as well as mRNA.

Effect of administration of a controlled-release monensin capsule on incidence of calving-related disorders, fertility, and milk yield in dairy cows

OBJECTIVE

To determine the effect of a controlled-release monensin capsule administered at cessation of lactation on incidence of calving-related disorders, fertility, and milk yield in dairy cows.

ANIMALS

290 dairy cows treated with monensin and 290 untreated control cows.

PROCEDURE

Treated cows received a capsule that released monensin at 335 mg/d for 95 days. Incidence of calving-related disorders; daily milk yield up to 20 days postpartum; test-day milk yield, fat, protein, and mature-equivalent 305-day milk production; and body condition score at calving were determined. Reproductive variables were conception rate at first service, pregnancy rate, and calving-to-conception interval.

RESULTS

Cows treated with monensin were 2.1 times as likely to develop dystocia and 0.8 times as likely to develop metritis as control cows. For milk yield, there was an interaction of treatment X time X parity. In multiparous cows, monensin significantly improved milk yield at test days 4 and 7. In addition, monensin increased body condition score at calving.

CONCLUSIONS AND CLINICAL RELEVANCE

Despite increasing the likelihood of developing dystocia and metritis, administration of monensin improved the lactational performance of multiparous cows and may be a promising additive for use at the time of cessation of lactation.

Effects of Dietary Cation-Anion Difference on Intake, Milk Yield, and Blood Components of the Early Lactation Cow

Early lactation Holsteins cows (15 primiparous and 18 multiparous) were offered rations with dietary cation-anion difference, calculated as mEq (Na + K - Cl - S)/100 g of feed dry matter (DCAD:S), of 20, 35, or 50 mEq from d 0 (calving) to 42 d postpartum (August 20, 2000 to January 9, 2001) to determine the effects of increasing DCAD:S on dry matter intake (DMI), milk yield, and blood metabolites. For DCAD:S of 20, 35, and 50, DMI was 3.30, 3.38, 2.96 kg/100 kg of body weight (BW); milk yield was 25.5, 24.2, and 22.4 kg/d, respectively. No differences were observed for concentration or yield of milk fat or milk protein. Serum Ca, P, Mg, Na, K, Cl, cation-anion difference, insulin, and glucose did not differ with DCAD. Serum HCO3- was 26.07, 25.88, and 27.64 mEq/L for 20, 35, and 50 DCAD:S. Serum Ca, Mg, Na, and K concentrations were greater for primiparous cows (9.52 mg/dL, 2.35 mg/dL, 140.03 mEq/L, 4.66 mEq/L, respectively) than for multiparous cows (9.27 mg/dL, 2.12 mg/dL, 137.63 mEq/L, 4.46 mEq/ L, respectively). A DCAD:S between 23 and 33 mEq/100 g of dry matter (DM) appears to be adequate during cool weather for the milk yield that occurred in the present study based on DMI (kg/100 kg of BW), whereas DCAD:S of 50 mEq/100 g of DM may be excessive and could be too alkaline or unpalatable, resulting in decreased DMI (kg/100 kg of BW).

Influência do balanço cátion-aniônico da dieta no rúmen e no desempenho de ovinos

Estudou-se o efeito do balanço cátion-aniônico da dieta (BCAD) no desempenho animal e na fermentação ruminal, utilizando-se 25 carneiros machos, da raça Santa Inês, durante 75 dias. O delineamento experimental foi em blocos ao acaso, com cinco tratamentos. Para a manipulação do BCAD, foram adicionados sulfato de amônio e bicarbonato de sódio, obtendo-se os seguintes tratamentos: -160, -40, 140, 250 e 500 mEq/kg de matéria seca. O aumento do BCAD resultou em aumentos da ingestão de matéria seca, do ganho diário, da eficiência alimentar e do pH ruminal (P<0,05). O perfil de ácidos graxos ruminais não foi afetado pelo BCAD.

Effect of a commercial anion dietary supplement on acid-base balance, urine volume, and urinary ion excretion in male goats fed oat or grass hay diets

OBJECTIVE

To determine whether feeding a commercial anionic dietary supplement as a urinary acidifier to male goats may be useful for management of urolithiasis.

ANIMALS

8 adult sexually intact male Toggenburg, Saanen, and Nubian goats.

PROCEDURE

Goats were randomly assigned by age-, breed-, and weight-matched pairs to an oat or grass hay diet that was fed for 12 days. On days 13 to 14 (early sample collection time before supplementation), measurements were made of blood and urine sodium, potassium, calcium, magnesium, chloride, phosphorus, and sulfur concentrations; blood and urine pH; urine production; and water consumption. During the next 28 days, the anionic dietary supplement was added to the oat and grass hay diets to achieve a dietary cation-anion difference of 0 mEq/100g of dry matter. Blood and urine samples were analyzed during dietary supplementation on days 12 to 13 (middle sample collection time) and 27 to 28 (late sample collection time).

RESULTS

Blood bicarbonate, pH, and urine pH of goats fed grass hay and goats fed oat hay were significantly decreased during the middle and late sample collection times, compared with the early sample collection time. Water consumption and urine production in all goats increased significantly during the late sample collection time, compared with the early sample collection time.

CONCLUSIONS AND CLINICAL RELEVANCE

The anionic dietary supplement used in our study increases urine volume, alters urine ion concentrations, and is an efficacious urinary acidifier in goats. Goats treated with prolonged anionic dietary supplementation should be monitored for secondary osteoporosis from chronic urinary calcium loss.

Influência da diferença cátion-aniônica da dieta sobre o balanço de cálcio, fósforo e magnésio em ovinos

O efeito do balanço cátion-aniônico da dieta (BCAD) no balanço macromineral (cálcio, fósforo e magnésio), no pH urinário e fecal, na concentração sérica de cálcio, fósforo e magnésio foi estudado utilizando-se 16 carneiros machos, da raça Santa Inês, por um período de 26 dias, sendo sete de adaptação. O delineamento experimental foi em blocos ao acaso, com quatro tratamentos. Para a manipulação do BCAD foram adicionados cloreto de cálcio e bicarbonato de sódio, obtendo-se os seguintes tratamentos: -12; +30; +76 e +133mEq/kg MS da ração. Não foram encontradas diferenças (P>0,10) no pH fecal, pH urinário, balanço de fósforo e magnésio. Com o aumento do BCAD houve decréscimo da absorção e retenção de cálcio, e aumento da excreção fecal. A manipulação do BCAD interferiu no metabolismo de macrominerais, principalmente no de cálcio.