Interactions of dietary cation-anion balance and phosphorus: effects on growth and serum inorganic phosphorus in dairy calves

Thirty-six male and female Holstein and Jersey calves were assigned at weaning to a randomized complete block design in a 2 x 3 factorial arrangement to evaluate the influence of two dietary cation-anion balances (-14 and +39 meq(Na + K)-(Cl + S) per 100 g diet DM) and three amounts of dietary P (.22, .29, and .37%) on performance and P metabolism from 9 to 19 wk of age. Feed intake, average daily gain, and serum inorganic P were higher on the anionic diets and increased with increasing dietary P. Body weights were higher on the .37% P diets by wk 3 and on the anionic diets by wk 6. The interaction of dietary P and cation-anion balance was responsible for significant differences in calf performance; the anionic diet exhibited marked improvement over the cationic diet at the lowest P concentration. Results indicate that the availability of P for young dairy calves may be higher with anionic than cationic diets.     

Effects of manipulating dietary cation-anion balance on macromineral balance in sheep.

Effect on macromineral balance in sheep of dietary excess of inorganic anions (Cl and S) or inorganic cations (Na and K) was studied. Dietary cation-anion balance was calculated as milliequivalents [(Na + K) - (Cl + S)] kg-1 of DM. Eight crossbred wethers were fed two levels of Ca, designated high Ca (.82%) or normal Ca (.48%), with four treatment each, three of which differed in dietary cation-anion balance. Control and two treatments had +284, +61, and -27 meq kg-1 of DM for high Ca and +343, +218, and +63 meq kg-1 of DM for normal Ca, respectively. A fourth treatment was control plus injection of vitamin D3 (16,670 IU kg-1 of BW). Reducing dietary cation-anion balance reduced Ca retention by increasing excretion of urinary Ca. Apparent absorption of Ca was similar across cation-anion balances. There was no correlation observed between dietary cation-anion balance and concentration of plasma Ca. No difference was observed in apparent absorption of Ca between high and normal Ca. This result may be related to an oversupply of dietary Ca. Magnesium retention as a proportion of that absorbed for lowest cation-anion balance was smaller than that for the intermediate balance and control plus vitamin D3, although not different from control. Results showed that reduced dietary cation-anion balance resulted in a reduction of Ca retention.     

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 × 6 Latin square design with a 2 × 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.     

Dietary cation-anion difference effects on performance and acid-base status of dairy cows postpartum

Our objective was to examine the effect of dietary cation-anion difference (DCAD) on performance and acid-base status of cows postpartum. Sixteen Holstein and 8 Jersey multiparous cows were used immediately after calving to compare 2 DCAD [22 or 47 milliequivalents (Na + K − Cl − S)/100 g of dry matter (DM)] in a completely randomized design. The corn silage-based diets were formulated to contain 19.0% crude protein, 25.4% neutral detergent fiber, 15.0% acid detergent fiber, and 1.69 Mcal of net energy for lactation per kilogram (on a DM basis). An additional 2.3 kg of alfalfa hay was fed during the first 5 d postpartum, and then milk, blood, and urine samples were collected weekly for 6 wk. Repeated-measures (with an extra between-cow effect) mixed model analysis indicated that DCAD did not affect DM intake (18.2 and 18.3 kg/d), milk production (33.5 and 33.3 kg/d), milk composition (3.96 and 4.11% fat, 3.11 and 3.00% protein, and 8.95 and 8.83% solids-not-fat), jugular venous blood pH (7.395 and 7.400), HCO₃⁻ concentration (27.3 and 27.6 mEq/L), or partial pressure of CO₂ (46.7 and 46.5 mmHg). Elevated coccygeal venous plasma branched-chain AA (431 and 558 μM) and ratio of essential AA to total AA (0.390 and 0.434) in cows with DCAD of 22 vs. 47 mEq/100 g of DM indicated that N metabolism in the rumen was affected, probably resulting in more microbial protein flowing to the small intestine. Urinary pH tended to increase with DCAD (8.12 vs. 8.20). Higher net acid excretion in cows with DCAD of 22 vs. 47 mEq/100 g of DM (−24 and −41 mM:mM) suggested that net acid excretion was much more indicative of acid load than blood acid-base parameters in cows postpartum. Intake of DM and performance of cows postpartum were not improved when DCAD increased from 22 to 47 mEq/100 g of DM, likely because cows immediately after calving respond more variably to dietary treatments and that makes treatment effects difficult to detect.     

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

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

Dietary cation-anion balance and cation source effects on production and acid-base status of heat-stressed cows.

Two 4 x 4 replicated Latin square studies, each containing 8 lactating Holstein cows, were conducted simultaneously in south Georgia during the summer. The effects of dietary cation source (Na or K) and increasing dietary cation-anion balance (milliequivalents of Na + K - Cl per kilogram of feed DM) within cation source (control = 120.4 meq/kg of feed DM; Na source = 219.7, 347.8, 464.1 meq/kg of feed DM; K source = 231.2, 352.6, 456.0 meq/kg of feed DM) were determined on performance and acid-base chemistry during hot, humid weather. Cow body temperatures were elevated by environmental conditions but were not affected by dietary cation-anion balance. Differences in body temperature from dietary cation source probably were related to differences in cow BW. Intake of DM increased linearly, but yields of milk and FCM did not change with increasing dietary cation-anion balance, and cation source had no effect. Milk fat and protein percentages were not altered by dietary cation-anion balance, and greater milk fat and protein percentages from cows offered the Na versus K source diets probably were due to differences between cows in the two Latin squares. Alterations in blood acid-base chemistry with increasing dietary cation-anion balance were as expected. Greater blood buffering capacity, indicated by blood base excess and bicarbonate content, may be responsible for the improved feed intake.     

Effect of dietary cation-anion difference on acid-base status and dry matter intake in dry pregnant cows

The objective was to determine if the reduction in dry matter (DM) intake of acidogenic diets is mediated by inclusion of acidogenic products, content of salts containing Cl, or changes in acid-base status. The hypothesis was that a decrease in intake is mediated by metabolic acidosis. Ten primigravid Holstein cows at 148 ± 8 d of gestation were used in a duplicated 5 × 5 Latin square design. The dietary cation-anion difference (DCAD) of diets and acid-base status of cows were manipulated by incorporating an acidogenic product or by adding salts containing Cl, Na, and K to the diets. Treatments were a base diet (T1; 1.42% K, 0.04% Na, 0.26% Cl; DCAD = 196 mEq/kg); the base diet with added 1% NaCl and 1% KCl (T2; 1.83% K, 0.42% Na, 1.23% Cl; DCAD = 194 mEq/kg); the base diet with added 7.5% acidogenic product, 1.5% NaHCO₃, and 1% K₂CO₃ (T3; 1.71% K, 0.54% Na, 0.89% Cl; DCAD = 192 mEq/kg); the base diet with added 7.5% acidogenic product (T4; 1.29% K, 0.13% Na, 0.91% Cl; DCAD = ?114 mEq/kg); and the base diet with 7.5% acidogenic product, 1% NaCl, and 1% KCl (T5; 1.78% K, 0.53% Na, 2.03% Cl; DCAD = ?113 mEq/kg). Periods lasted 14 d with the last 7 d used for data collection. Feeding behavior was evaluated for 12 h in the last 2 d of each period. Reducing the DCAD by feeding an acidogenic product reduced blood pH (T1 = 7.450 vs. T2 = 7.436 vs. T3 = 7.435 vs. T4 = 7.420 vs. T5 = 7.416) and induced a compensated metabolic acidosis with a reduction in bicarbonate, base excess, and partial pressure of CO₂ in blood, and reduced pH and strong ion difference in urine. Reducing the DCAD reduced DM intake 0.6 kg/d (T1 = 10.3 vs. T4 = 9.7 kg/d), which was caused by the change in acid-base status (T2 + T3 = 10.2 vs. T4 + T5 = 9.6 kg/d) because counteracting the acidifying action of the acidogenic product by adding salts with strong cations to the diet prevented the decline in intake. The decline in intake caused by metabolic acidosis also was observed when adjusted for body weight (T2 + T3 = 1.75 vs. T4 + T5 = 1.66% BW). Altering the acid-base status with acidogenic diets reduced eating (T2 + T3 = 6.7 vs. T4 + T5 = 5.9 bouts/12 h) and chewing (T2 + T3 = 14.6 vs. T4 + T5 = 13.5 bouts/12 h) bouts, and extended meal duration (T2 + T3 = 19.8 vs. T4 + T5 = 22.0 min/meal) and intermeal interval (T2 + T3 = 92.0 vs. T4 + T5 = 107.7 min). Results indicate that reducing the DCAD induced a compensated metabolic acidosis and reduced DM intake, but correcting the metabolic acidosis prevented the decline in DM intake in dry cows. The decrease in DM intake in diets with negative DCAD was mediated by metabolic acidosis and not by addition of acidogenic product or salts containing Cl.     

Dietary cation-anion difference effects on performance and acid-base status of lactating dairy cows: a meta-analysis

A meta-analysis was conducted to examine potential empirical relationships between dietary cation-anion difference (DCAD) (Na + K - Cl) and the response of lactating dairy cows. The database was developed from 12 studies published between 1984 and 1997 that included a total of 17 trials, 69 dietary treatments, and 230 cows. Results indicated that DCAD affected performance of lactating dairy cows. Maximum milk yield and feed intake were reached when DCAD was 34 and 40 meq/100 g of feed dry matter, respectively. Blood pH and HCO3 concentrations increased with DCAD, indicating an improved acid-base balance of lactating dairy cows. Changes in urinary pH and urinary excretion of Na, K, and Cl were consistent with varying DCAD, thus dietary acidity or alkalinity. The effects of DCAD were likely mediated via modification of acid-base status in the cows.     

Influence of cation-anion balance on feed intake, body weight gain, and humoral response of dairy calves.

The objective of this study was to examine the influence of diets with varying cation-anion balance on performance and humoral responses in young, growing dairy calves. Twenty-eight Holstein and 4 Jersey female calves were blocked at 56 to 70 d after birth according to breed and age and assigned randomly to dietary treatments of 0, 21, 37, and 52 meq(Na + K) - Cl/100 g of dietary DM. Diets were based on cracked corn, dried brewers grains, and oats and were fed for 8 wk. Feed intake and average daily gain tended to increase quadratically, being highest for calves fed the +37-meq diet and lowest for those fed the 0-meq diet. Blood and urine pH increased linearly with increasing dietary cation-anion balance. Plasma Ca increased linearly, and Mg and Cl decreased linearly with increasing cation-anion balance. Plasma Na and P were unaffected by dietary treatments. Urinary Ca, Mg, and Cl excretions decreased linearly; urinary P, Na, and K excretion increased linearly with increasing dietary cation-anion balance. Blood pH increased linearly with increasing dietary cation-anion balance. Blood partial pressure of CO2 and HCO3 increased concurrently with increasing dietary cation-anion balance. Results indicate that altering cation-anion balance may impact DMI and average daily gain in the young ruminant.     

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.     

Effects of dietary cation-anion difference on ruminal metabolism and blood acid-base regulation in dairy cows receiving 2 contrasting levels of concentrate in diets

Dietary cation-anion difference [DCAD = Na + K − Cl in mEq/kg of dry matter (DM)] increases DM intake (DMI) in cows fed diets containing rapidly degraded starch. Increased DMI of diets containing rapidly degraded starch could potentially exacerbate subacute acidosis. The objective of this study was to determine metabolic effects of increasing DCAD in low and high starch diets. Six cannulated Holstein cows were blocked into 2 groups of 3 cows and assigned to two 3 × 3 Latin squares in a split-plot design. Each group received a level of concentrate at either 20 or 40% on a DM basis. The diet containing 20% concentrate supplied 4% rapidly degraded starch, whereas the diet containing 40% concentrate supplied 22% rapidly degraded starch. Diets in each square were formulated to provide a DCAD of 0, 150, or 300 mEq/kg of DM. The 3 values were obtained by manipulating Na and Cl contents. Increasing the proportion of rapidly degraded starch decreased rumen pH and the acetate to propionate ratio but did not affect digestibility, blood acid-base status, pH of urine, and strong ion excretion. Increasing DCAD increased DMI, the effect being higher when the cows were fed the 40% concentrate diet. Increasing DCAD did not affect mean ruminal pH, molar proportion of VFA, and fiber digestibility; reduced the range of rumen pH decrease during the meal in cows fed the 40% concentrate diet; and strongly increased blood pH and blood HCO₃ concentration. Increasing DCAD increased urine pH and modified the urinary excretion of minerals. With low DCAD, 70% of Cl and only 16% of Na were excreted in urine whereas with high DCAD, 33% of Cl and 53% of Na were excreted. These results suggest that DMI of cows fed diets rich in rapidly degraded starch and low DCAD was limited to maintain the blood pH in a physiological range. Increasing DCAD allowed the cows to increase DMI because of the ability of positive DCAD to maintain blood acid-base status. A localized rumen buffering effect could not be excluded and could be linked with a higher amount of HCO₃ recycled into the rumen. Main mechanisms involved in regulating blood pH might be renal excretion of protons and strong ions and renal HCO₃ reabsorption.     

Effects of maternal level of dietary cation-anion difference fed to prepartum nulliparous cows on offspring acid-base balance,metabolism, and growth

The objectives were to determine the effects of dietary cation-anion difference (DCAD) fed to pregnant cows during the last 22 d of gestation on offspring acid-base balance, metabolism, growth, and health preweaning. A total of 132 nulliparous Holstein cows were enrolled at 250 (248 to 253) d of gestation in a randomized block design. Cows were blocked by genomic merit of energy-corrected milk yield and assigned randomly to diets varying in DCAD: +200 (P200, n = 43), ?50 (N50, n = 45), or ?150 (N150, n = 44) mEq/kg of dry matter (DM). Newborn calves (15 males and 28 females in P200, 22 males and 23 females in N50, and 18 males and 26 females in N150) were followed for the first 7 or 56 d of age if males or females, respectively. Measures of acid-base balance and concentrations of minerals in blood were measured in all calves on d 0 before colostrum feeding, and on d 1, 3, and 7. Each calf was fed 3.78 L of colostrum from the respective treatment, and apparent efficiency of IgG absorption was determined. All calves were weighed at birth, and females were weighed again at 21, 42, and 56 d of age. Concentrations in serum of total calcium (tCa), total magnesium (tMg), and total phosphorus (tP) were measured up to 56 d of age; intakes of milk and starter grain DM were measured daily from 21 to 56 d of age; and incidence of disease was recorded for the first 56 d of age in females. Treatment did not affect acid-base balance measured in all calves. Calves were born with metabolic and respiratory acidosis, which reversed by 1 d of age. In the first 24 h after birth, blood pH increased from 7.215 to 7.421 and bicarbonate from 26.2 to 31.7 mM, whereas partial pressure of CO₂ decreased from 64.1 to 48.7 mm of Hg in all treatments. Maternal DCAD did not affect colostrum IgG content fed to calves (P200 = 95.0 vs. N50 = 91.0 vs. N150 = 97.1 ± 4.1 g/L) or apparent efficiency of IgG absorption (P200 = 33.1 vs. N50 = 33.1 vs. N150 = 34.2 ± 1.9%). Males were born heavier than females, but maternal DCAD did not affect birth weight of all calves (P200 = 37.7 vs. N50 = 37.3 vs. N150 = 37.8 ± 0.7 kg) or daily weight gain in females in the first 56 d of life (P200 = 0.80 vs. N50 = 0.81 vs. N150 = 0.77 ± 0.03 kg/d). Treatment did not affect intake of milk (P200 = 1.11 vs. N50 = 1.04 vs. N150 = 1.19 ± 0.06 kg/d) or starter grain DM (P200 = 0.27 vs. N50 = 0.27 vs. N150 = 0.21 ± 0.06 kg/d), or measures of feed efficiency. Treatment did not affect concentrations of minerals in serum, morbidity, or age at morbidity. Manipulating the DCAD of pregnant nulliparous dams during late gestation did not affect offspring performance in the first 2 mo of age.     

Influence of dietary cation-anion balance on milk, blood, urine, and rumen fluid in lactating dairy cattle

Twelve lactating Holstein cows were blocked according to age and milk production into groups of three cows and assigned to three 4 x 4 Latin squares in a split-plot design with subtreatments. Treatments on each square were four diets formulated to provide -10, 0, +10, or +20 meq/Na + K) -Cl/100 g diet DM. The four balances were achieved on squares 1, 2, and 3 by manipulating Na, K, and Cl, respectively. Actual milk yield was 8.6% higher on +20 than -10 averaged across the three squares. Blood pH and bicarbonate increased linearly with dietary cation-anion balance. Rumen pH increased linearly with dietary cation-anion balance, but fermentation patterns were largely unaffected. Urine pH increased linearly and quadratically with increasing dietary cation-anion balance. Square times balance response differences proved nonsignificant for all parameters except blood bicarbonate and rumen isovalerate, indicating responses could be attributed to the dietary cation-anion balance itself rather than to the effects of a single ion. Regulation of dietary cation-anion balance may become a useful tool for improving the performance of lactating dairy cattle.     

Amounts and sources of protein for dairy calves.

Female Holstein calves (178) were fed rations varying from 10 to 17% crude protein (air dry) from 30 to 102 days of age. Ten percent was inadequate resulting in less body weight, gain, withers height, and heart girth than rations containing 12 to 17% crude protein. In trial 1 addition of urea, biuret, or ammonia-molasses to a 12% diet to make a 16% crude protein diet allowed gains and weights indistinguishable from those on a 12 or 16% crude protein soybean meal ration. In another trial, addition of urea, biuret, or ammonium propionate to a 10% ration to make a 14% ration allowed insignificantly greater gains and body weight. Gains and body weight were greater for the 14% soybean meal ration than the three non-protein-nitrogen rations for calves to 71 days of age but equal for 71 to 102 days. Gain, body weight, dry matter, and protein intakes at most dates and intervals were greater for calves fed the 14% soybean meal ration than the 10% ration. When 10, 12, 14, and 16% soybean meal rations were compared simultaneously, only the 10% crude protein ration gave inferior performance. Gains were reduced when average daily crude protein intake for the 72 day trail was 258 g or less. Calves fed lupine or dried poultry waste did not gain or consume as much as those fed comparable soybean meal rations. Calves fed a 17% crude protein ration from several protein sources plus alfalfa hay gained no much than those fed the 12 to 16% crude protein rations. Regression analysis relating dry matter and protein intake to body weight or gains indicated both dry matter intake and protein percentage were about equally important from day 41 to 72 and that after this age dry matter intake was of much greater importance than protein percentage. Protein intake expressed as g/day was not of importance in this regression. Weaning at day 42 allowed for greater body weight and gains than weaning at day 32. The difference in body weight was 2.5 kg at day 42 and 7 kg at day 102.     

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 × 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°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.     

Effects of prepartum dietary cation-anion difference intake on production and health of dairy cows: A meta-analysis

Prepartum diets influence cow performance for weeks to months postpartum. This observation leads to questions about milk yield and physiological and health responses to diets with negative dietary cation-anion difference (DCAD). Further, responses to increased intake of a diet with lower DCAD (Eq/d) have not been explored using meta-analysis. Our objectives were to explore the effects of prepartum DCAD intake on metabolism and production and health as well as the potential for differences in intake of other macrominerals to influence responses to differences in DCAD intake using classical meta-analytical methods. Not all treated groups were fed a diet with negative DCAD, and the effect studied is that of reducing the DCAD. We hypothesized that reducing DCAD intake would improve Ca metabolism and postpartum performance. We used a maximum of 58 comparisons from 31 experiments and a total of 1,571 cows. Intakes of DCAD were 2.28 Eq/d and ?0.64 Eq/d for the control, higher DCAD and treated, lower DCAD groups, respectively. Diets with lower DCAD reduced urine pH [standardized mean difference (SMD) = 1.90 and weighted mean difference (WMD) ?1.23 pH]. Intake of lower DCAD decreased prepartum DMI (SMD = 0.23; WMD = 0.29 kg/d), increased postpartum DMI (SMD = 0.40; WMD = 0.63 kg/d), and increased milk yield (SMD = 0.172). However, we found an interaction with parity; diets with lower DCAD increased milk yield in parous cows (SMD = 0.29; WMD = 1.1 kg/d) but resulted in numerically lower milk yield in nulliparous cows (SMD = ?0.20; WMD = 1.28 kg/d) compared with controls. The FCM yield increased with treatment (SMD = 0.12; WMD = 0.56 kg/d); however, yield of treated cows tended to be greater in parous cows but smaller for nulliparous cows compared with controls. Milk fat percentage, milk fat yield, and milk protein percentages were not affected by treatment, although milk protein yield tended to increase in cows fed the lower DCAD diet (SMD = 0.21; WMD = 0.02 kg/d). Treatment increased blood Ca (SMD = 0.53; WMD = 0.13 mM) and P (SMD = 0.40; WMD = 0.13 mM) on the day of calving and Ca postpartum (SMD = 0.36; WMD = 0.06 mM). Treated cows had smaller concentration of blood BHB before calving than controls (SMD = ?0.39; WMD = ?0.04 mM). Reducing DCAD in cows resulted in decreased risks of clinical hypocalcemia (risk ratio = 0.60) and retained placenta (risk ratio = 0.59), and reduced the odds of metritis (odds ratio = 0.46) and overall disease (OR = 0.61). We observed no effect on risk of abomasal displacement or mastitis and no effect of differences between treated and control cows in Ca intake (g/d) on the outcomes evaluated. A positive role for increased Mg intake between groups for increased milk fat yield and in reducing the risk of retained placenta was identified. Diets with lower DCAD improved performance of parous dairy cows, and our findings suggest a need for more studies on the effects of a lower DCAD on nulliparous transition cows.     

Effects of continuous versus periodic milk availability on behavior and performance of dairy calves

Dairy calves fed milk ad libitum engage in feeding activity throughout the day and night. However, providing calves with continuous access to milk can present practical problems with milk quality, particularly during warm weather. One way to maintain milk quality in ad libitum feeding regimens is to limit the time that milk is available, but no research to date has addressed how this might affect calves. The objectives of this study were to quantify the effects of continuous access to milk (24 h/d) vs. access during only part of the day on milk feeding behavior and performance. Twenty-eight female Holstein calves were randomly assigned to treatments at 5 ± 3 d of age and monitored for 28 d. All calves had milk delivered through a teat. Treatments were 1) access to milk for 24 h/d; 2) access to milk for 2 feedings per day (each of 2 h), with water available through the teat the remainder of the day (4-h wet treatment); and, 3) access to milk for 2 feedings per day (each of 2 h), but with no water available through the teat (4-h dry treatment). Calves given 24-h access to milk consumed 11.2 ± 0.5 kg/d on average. Milk intake tended to be lower for the 4-h wet and 4-h dry treatments, averaging 10.0 ± 0.3 kg/d, with no difference between these 2 treatments in this or any other variable. Average daily gain over the course of the experiment did not vary with treatment and averaged 1.1 ± 0.04 kg/d. Calves in the 24-h treatment spent more time on the teat than those calves on the 4-h treatments, but during the 4 h/d when milk was available to all calves, calves in the 4-h treatments spent more time on the teat. These results show that individually housed calves fed milk ad libitum for only 4 h/d compensate by changing their milk feeding behavior and are able to achieve similar weight gains to animals fed milk continuously.     

Role of magnesium in the dietary cation-anion balance equation for ruminants

Eight midlactation Holstein cows (four primiparous) were assigned to replicated 4 x 4 Latin squares with a 2 x 2 factorial arrangement of treatments. The basal diet was formulated to contain 0 milliequivalents (Na + K) - Cl/100 g of diet DM. Treatment diets of high and low dietary cation-anion balance were achieved by adding appropriate amounts of supplemental Na + K (added on an equivalent basis) or Mg to the basal diet. Milk and protein yield were increased as well as DMI and FCM for Na + K diets The high concentration of cation increased milk fat percentage. The cation-anion balance (using Mg as a cation) had no effect on any of the production parameters observed. The higher cation-anion balances increased blood bicarbonate levels and plasma Na. Urinary Ca excretion was increased for the Mg diets. Urinary pH increased with both the source of cation (Na + K) and the concentration of cation (high) in the diet. other minerals were unaffected in milk, plasma, or urine. Responses measured in this trial reflect treatments calculated using the equation milliequivalents (Na + K) - Cl/100 g diet DM or (Na + K) - (Cl + S)/100 g diet DM, suggesting that Mg plays a minor role in dietary cation-anion balance.     

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 × 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.     

Effects of dietary aflatoxin and zinc on enzymes and other blood constituents in dairy calves

Young male Holstein calves were fed diets containing 40 or 640 ppm zinc with 0 or 5 ppm aflatoxin for 3 wk. The aflatoxin mixture contained 80.5% B1 and the calves consumed 143 mg of B1 over 3 wk. Plasma glutamic-oxaloacetic transaminase and alkaline phosphatase concentrations were increased substantially, and lactic dehydrogenase was reduced in aflatoxin-fed calves. Supplemental zinc partially counteracted the effect of aflatoxin on these enzymes. Hemoglobin, packed cell volume, and total solids in blood plasma were increased in aflatoxin-fed calves, but high dietary zinc had no effect on these blood constituents. Glucose in plasma was reduced in calves receiving aflatoxin. High dietary zinc was only partially effective in protecting against the reduced glucose effect for about 1 wk. Total protein, albumin, globulin, ratio of albumin/globulin in blood plasma, and liver lipid were not affected by aflatoxin. Several enzymes and blood constituents are affected by aflatoxin in calves. The protection of zinc against aflatoxicosis appears to be no more than a partial effect.