Effects of altering dietary cation-anion difference on calcium and energy metabolism in peripartum cows

Our objective was to determine the effects of varying dietary cation-anion differences (DCAD: meq[(Na + K) - (Cl + S)]/100 g of dry matter) in prepartum diets on Ca, energy, and endocrine status prepartum and postpartum. Holstein cows (n = 21) and heifers (n = 34) were fed diets with varying amounts of CaCl2, CaSO4, and MgSO4 to achieve a DCAD of +15 (control), 0, or -15 meq/100 g of dry matter for the last 24 d before expected calving. Dietary Ca concentration was increased (by CaCO3 supplementation) with decreasing DCAD. Plasma ionized Ca concentrations prepartum and at calving in both cows and heifers increased with reduced DCAD in the diet. At calving, plasma ionized Ca concentration was 3.67, 3.85, and 4.35 for cows and 4.44, 4.57, and 4.62 mg/dl for heifers fed diets containing +15, 0, and -15 DCAD, respectively. All heifers had normal concentrations of plasma ionized Ca (>4 mg/dl) at calving. Also at calving, plasma concentrations ofparathyroid hormone and calcitriol were less in cows and heifers fed diets containing reduced DCAD, but the plasma concentration of hydroxyproline was not affected by diet. Prepartum dry matter intake, energy balance, and body weight gains were lower and concentration of liver triglyceride was higher for heifers but not cows fed the -15 DCAD diet. Also, nonesterified fatty acids the last week prepartum were positively correlated with liver triglyceride for heifers but not cows. Feeding of anionic salts plus CaCO3 to reduce DCAD to -15 and increase Ca in prepartum diets prevents hypocalcemia at calving in cows, but decreases prepartum dry matter intake and increases the concentration of liver triglyceride in heifers. That heifers maintained calcium homeostasis at calving regardless of diet but ate less when fed the -15 DCAD diet suggests that they should not be fed anionic salts before calving.     

Parturient hypocalcemia in jersey cows fed alfalfa haylage-based diets with different cation to anion ratios

Jersey cows were fed three alfalfa haylage-based diets with different cation-anion balances beginning 6 wk preceding third or later calving and ending 24 to 36 h postpartum. Sodium and Cl as percentages of dietary DM were .08 and 1.66 in diet 1 (anionic, 5 cows), .44 and .91 in diet 2 (intermediate, 6 cows), and 1.60 and .34 in diet 3 (cationic, 6 cows). Cation-anion balances were 22, 60, and 126 meq/100 g DM; Ca:P ratios averaged 4:1. Cows fed diet 1 in comparison with cows fed diets 2 or 3 over 6 wk had similar concentrations of Ca, P, and Na but higher concentrations of Mg and K in plasma and higher urinary excretions of Ca and Mg. Concentrations of 1,25-dihydroxyvitamin D 3 d before parturition were higher in cows fed diet 1 than in cows fed diets 2 or 3. Within 36 h after calving, mean concentrations of Ca in plasma (mg/dl, range) of cows fed diets 1 to 3, respectively, were 7 (8.7 to 6.2), 6.5 (7.8 to 3.9), and 6.3 (7.8 to 3.8). Number of cases of clinical milk fever by diet were 0 of 5, 2 of 6, and 1 of 6 cows. Alteration of dietary cation-anion balance by addition of Cl may effectively reduce incidence and severity of parturient hypocalcemia.     

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

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

Some blood minerals and hormones in cows fed variable mineral levels and ionic balance.

Eighty multiparous Holstein cows were assigned to eight treatments in a 2 x 2 x 2 factorial design to examine changes in serum parathyroid hormone, calcitonin, Ca, P, Mg, K, and Cl under two levels of dietary Ca and P with two anion-cation balances. Factor levels were low and high Ca (51 vs. 115 g/d), P (38 vs. 52 g/d), and cationic:anionic balance (23 vs. -8 meq). Cows were offered a TMR and an experimental mineral supplement to adjust mineral and anion-cation levels. Caudal vein blood samples were collected every 2 d from d -10 to +10 from calving. Serum K was lower for low Ca and high P compared with high Ca and low P treatments. Neither hormones nor the minerals examined in serum showed treatment effects. Cows of higher parity consumed less supplement and had lower serum Ca and P. All serum variables except calcitonin showed day to day variations. Both Ca and P decreased around parturition, whereas parathyroid hormone and Mg increased. Anionic diets did not differ from cationic diets regarding serum parathyroid hormone, calcitonin, Ca, P, Mg, K, Cl, or Na.     

1 alpha-hydroxyvitamin D3 plus 25-hydroxyvitamin D3 reduces parturient paresis in dairy cows fed high dietary calcium.

The effectiveness of a combination of 1 alpha-hydroxyvitamin D3 and 25-hydroxyvitamin D3 for reducing incidence of parturient paresis in aged Holstein cows was tested. Intramuscular injection of .5 mg of 1 alpha-hydroxyvitamin D3 plus 4 mg of 25-hydroxyvitamin D3 increased plasma 1,25-dihydroxyvitamin D concentrations through parturition. Treatment with 1 alpha-hydroxyvitamin D3 plus 25-hydroxyvitamin D3 raised prepartum serum Ca approximately 2 mg/dl and prepartum serum P approximately 4 to 5 mg/dl higher than untreated controls. Both treated and control cows had approximately a 2-mg/dl decrease in serum Ca following parturition. The prepartum diet of alfalfa silage and hay was supplemented with a grain mixture supplying 100 g of Ca/d from ground limestone. Under these dietary conditions, incidence of parturient paresis was reduced from 33 to 8%. In a separate experiment, treatment with 1 alpha-hydroxyvitamin D3 plus 25-hydroxyvitamin D3 did not reduce incidence of parturient paresis when cows consumed mixed diets of different feed-stuff composition. Further experiments are required to determine specifically the factor or factors responsible for the difference in response to active vitamin D compound administration between the two experiments. Prepartum dietary Ca intake may be one such factor.     

Influence of sodium chloride or potassium chloride on systemic acid-base status, milk yield, and mineral metabolism in lactating dairy cows

Our objective was to evaluate the response of lactating dairy cows to dietary Na, K, and Cl while holding cation-anion balance constant. Fifteen lactating Holstein cows, blocked according to age and previous milk yield, were assigned randomly to replicated 3 x 3 Latin squares with experimental periods of 3 wk. Diets contained sorghum silage and concentrate in a 40:60 ratio (DM basis) and were formulated to provide +32 meq of [(Na + K) - Cl]/100 g diet DM via one of three variations: 1) basal concentrations of dietary Na, K, and Cl, 2) basal diet with addition of 20 meq of Na and 20 meq of Cl/100 g in the form of 1.17% added NaCl, or 3) basal diet with the addition of 20 meq of K and 20 meq of Cl/100 g in the form of 1.56% added KCl. Free proton concentration in blood was increased by addition of NaCl and KCl; however, this increase did not appear to be physiologically significant, and no other measures of acid-base status were significantly affected. Plasma K was higher and plasma Mg was lower for the diets with supplemental NaCl or KCl than for basal diet. Urine mineral excretion reflected dietary mineral concentration, except Ca and Mg excretion rates were reduced by feeding the KCl diet. Milk yield reflected DM intake, which was lowest with supplemental NaCl. Results of this study indicate that, at a dietary cation-anion balance of +32 meq/100 g of diet DM, the balance of Na and K to Cl in the diet is a more important determinant of dietary impact on systemic acid-base status than actual dietary concentrations of Na, K, and Cl.     

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 prepartum dietary calcium level on calcium and magnesium metabolism in periparturient dairy cows

The aim of this study was to investigate the effects of dietary Ca level (4.9, 9.3, and 13.6 g/kg of DM) on Ca and Mg homeostasis in dairy cows around parturition. Cows of the Swedish Red breed (n = 29) with no previous veterinary treatment for milk fever were divided into 3 groups, and each group was fed one of the different diets during the last 15 to 32 d of gestation. Calcium was added as ground limestone, and the Mg concentration was 1.8 g/kg of DM in all diets. After calving the cows were fed similar diets. Plasma was sampled twice per week until calving, and 6, 12, and 24 h, 2, 4, and 7 d after calving. Spot urine samples were collected twice weekly until calving and creatinine was used as a marker of daily urinary excretion. Fecal samples were collected 2 times per day for 5 d starting 2 wk before expected calving, and acid-insoluble ash was used as an indigestible marker to estimate digestibility. Apparent digestibility of Mg and daily Mg excretion in the urine were lower in the dry period for cows fed the highest Ca level. Plasma Mg concentration was lower on 2, 4, and 7 d after calving in cows fed the highest level of Ca. Treatment groups did not differ in plasma Ca concentration, parathyroid hormone concentration, or bone mobilization, evaluated using crosslinked carboxyterminal telopeptides of type I collagen (CTx) as a marker. Plasma Ca concentration decreased and plasma CTx concentration increased 6 h after calving. The apparent digestibility of Ca during the dry period was not affected by dietary Ca, but the cows fed 4.9 g Ca/kg of DM excreted 1.2 g of Ca/d in the urine, which was higher compared with 0.4 g/d and 0.6 g/d for the cows fed 9.3 g of Ca/kg of DM and 13.6 g of Ca/kg of DM, respectively. The results show that feeding 13.6 g of dietary Ca/kg of DM impaired the Mg absorption during the dry period, and resulted in decreased plasma Mg concentration after calving, but prepartum dietary Ca level did not affect plasma Ca, parathyroid hormone, or CTx concentrations.     

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

Eight nonlactating, nonpregnant Jersey cows were used in a crossover experiment with two 28-d periods. The control diet consisted of corn silage plus a concentrate mix (68:32, DM basis). The treatment diet was the same, except that NH4Cl and (NH4)2SO4 (98 g of each/d per cow) were added to the concentrate. Cows fed the treatment diet had lower blood pH, higher ionized Ca in blood, and more urinary excretion of Ca, titratable acid, and ammonium than cows fed the control diet. For cows fed the treatment diet, ionized Ca in blood was greater after equal amounts of Na2-EDTA were infused to both treatment groups, and treatment cows recovered faster after infusion of Na2-EDTA was stopped than did control cows. The treatment diet induced mild metabolic acidosis and increased the cows' ability to maintain normal blood Ca concentrations; it potentially could reduce incidence of milk fever.     

Effect of prepartum dietary calcium on intake and serum and urinary mineral concentrations of cows

Nine multiparous and 12 primiparous cows were fed diets containing an anionic salt supplement and moderate Ca (0.99%) or high Ca (1.50%) concentrations for 21 d prepartum to determine the effects of dietary Ca concentration on serum and urine electrolytes and on postpartum intake and milk yield. Blood samples were collected during 21 to 1 d prepartum, 0 to 2 d postpartum, and 3 to 21 d postpartum. Dietary cation-anion difference (DCAD) for prepartum diets was approximately −6 mEq/100 g of dry matter (Na + K − Cl − S). Immediately postpartum, cows were fed diets with positive DCAD with greater than 1.00% Ca concentration. Mean serum Ca concentrations 21 to 1 d prepartum, 0 to 2 d postpartum, and 3 to 21 d postpartum were 9.62, 8.41, and 9.38 mg/dL. There were no treatment effects on serum Ca concentration. Mean serum Ca concentration was higher for primiparous than multiparous cows (9.34 vs. 8.93 mg/dL) for the trial and at calving (8.77 vs. 8.13 mg/dL). Mean serum HCO₃⁻ and urinary pH, respectively, were 20.32 mEq/L and 5.67 prepartum, 25.82 mEq/L and 7.62 at calving, and 26.08 mEq/L and 8.25 postpartum. No differences due to treatment were observed for serum and urinary concentrations of HCO₃⁻, pH, Mg, Na, K, and Cl. Milk yield was similar for 0.99 and 1.50% Ca treatments (22.8 and 20.7 kg/d). Diets containing 0.99 or 1.5% Ca maintained serum Ca at adequate levels around parturition and resulted in similar dry matter intake and postpartum milk yield.     

Impact of prepartum dietary phosphorus intake on calcium homeostasis at parturition

A study was conducted to determine the impact of dietary P intake on vitamin D metabolism and incidence of parturient paresis in aged dairy cows. Thirty dairy cows (10/group) were fed one of three experimental diets for approximately 28 d precalving. Phosphorus intake was .7, 1, or 3 times daily maintenance requirement and Ca intake was three times daily maintenance requirement for all cows. There was a 20% incidence of parturient paresis in each group. Prepartum dietary P intake had no effect on precalving or calving plasma Ca concentrations. Cows fed the low P (.7 times) diet had higher plasma Ca at 3 and 5 d postcalving than did cows fed P at 1 or 3 times maintenance. Plasma phosphorus concentrations reflected dietary P intake. Dietary P intake had no effect on plasma Mg, free hydroxyproline, 1,25-dihydroxyvitamin D, or 24,25-dihydroxyvitamin D concentrations. The range in dietary P from .7 to 3 times maintenance requirement had no effect on the incidence of parturient paresis. However, it did appear to influence Ca homeostasis during the postpartum period as cows fed the low P diet had higher plasma calcium concentrations postcalving. This may be a result of the low P diet enhancing intestinal C absorption by a vitamin D-mediated transport mechanism.     

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.     

Evaluating the inclusion of alfalfa hay in diets fed to multigravid Holstein cows in their transition to early lactation

The objectives of this study were to determine the dry matter intake (DMI), urine pH, Ca concentration in blood, Ca output in urine, and frequency of hypocalcemia in pregnant and nonlactating dairy cows consuming diets containing different hays and acidogenic products during the prepartum period. Eighty pregnant and nonlactating Holstein cows approaching their second or greater calving were fed 1 of 4 experimental diets according to a 2 × 2 factorial arrangement of treatments during the prepartum period (21 d before calving). Diets included either grass hay (GH) or alfalfa hay (AH) and calcium chloride (CL) or polyhalite (PO) as the acidogenic products. All diets had a dietary cation-anion difference (DCAD) below −190 mEq/kg of dry matter (DM). Grass hay contained 75 g/kg crude protein, 749 g/kg neutral detergent fiber, 3.6 g/kg Ca, 0.9 g/kg Na, 18.8 g/kg K, 3.8 g/kg Cl, 1.5 g/kg S, and a cation-anion difference equal to 290 mEq/kg of DM. Alfalfa hay contained 196 g/kg crude protein, 456 g/kg neutral detergent fiber, 15.2 g/kg Ca, 1.6 g/kg Na, 25 g/kg K, 7.7 g/kg Cl, 3.2 g/kg S, and a cation-anion difference equal to 292 mEq/kg of DM. Cows consuming GH tended to consume more DM than cows consuming AH (11.6 vs. 10.8 kg/d) but DMI did not differ between acidogenic products. Urine pH decreased below 6.5 for all diets, although cows consuming the GHPO diet had the highest urine pH. The concentration of Ca in plasma decreased substantially around calving but neither hay type nor acidogenic product affected it. Urinary Ca output was lowest for cows consuming the GHPO diet. No associations existed between dietary treatments and the frequencies of normocalcemia and hypocalcemia. Under the conditions of this study, in which alfalfa and grass hays had similar cation-anion differences, we concluded that the inclusion of alfalfa hay in prepartum diets does not necessarily increase the frequency of hypocalcemia. The cation-anion difference of the alfalfa hay, more than the concentration of potassium alone, may be a key determinant of whether alfalfa hay fits in a prepartum feeding program for prepartum dairy cows. Further research should explore this relationship.     

Effect of a metabolically created systemic acidosis on calcium homeostasis and the diurnal variation in urine pH in the non-lactating pregnant dairy cow

Reducing the dietary cation-anion difference (DCAD) has been shown to be an effective means of preventing parturient paresis in confinement systems where cows are offered a total mixed ration containing DCAD-reducing mineral compounds (anionic salts). Such a supplementation strategy is not possible in cows being group fed forages precalving, and little is known about the effect of supplementing these cows with large amounts of anionic salts twice daily.Eight non-lactating, pregnant Holstein-Friesian cows were allocated to two levels of DCAD (-20 and +18 meq/100 g DM) for 24 d, with an intensive Ca balance undertaken in metabolism stalls following a 2-week acclimatization to diet. The basal diet was 3 kg DM of crushed barley and 7 kg DM of pasture-hay. Urine and faeces were collected separately, weighed daily for 5 d and analysed for Ca content. Urinary Ca, creatinine and hydroxyproline concentration and plasma Ca concentration were determined during the period of the balance study. The diurnal pattern in urine and rumen pH was determined over 2 d. Decreasing DCAD reduced (P<0.001) the pH of urine, and increased (P<0.05) Ca absorption. Plasma Ca concentration was not affected by DCAD, and DCAD did not affect the output of urinary hydroxyproline, a marker of bone resorption. Twice-daily supplementation of anionic salts was sufficient to reduce the pH of blood and increase gastrointestinal Ca absorption. There was no diurnal variation in the pH of urine, suggesting that time of sampling to determine efficacy of DCAD in reducing systemic pH was not important.     

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.     

Effects of dietary phosphorus concentration during the transition period on plasma calcium concentrations,feed intake,and milk production in dairy cows

Our aim was to evaluate the effects of a low or high dietary phosphorus (P) concentration during the dry period, followed by either a high or low dietary P concentration during the first 8 wk of lactation, on plasma Ca concentrations, feed intake, and lactational performance of dairy cattle. Sixty pregnant multiparous Holstein Friesian dairy cows were assigned to a randomized block design with repeated measurements and dietary treatments arranged in a 2 × 2 factorial fashion. The experimental diets contained 3.6 (Dry-HP) or 2.2 (Dry-LP) g of P/kg of dry matter (DM) during the dry period, and 3.8 (Lac-HP) or 2.9 (Lac-LP) g of P/kg of DM during 56 d after calving period. In dry cows, plasma Ca concentrations were 3.3% greater when cows were fed 2.2 instead of 3.6 g of P/kg of DM. The proportion of cows being hypocalcemic (plasma Ca concentrations <2 mM) in the first week after calving was lowest with the low-P diets both during the dry period and lactation. Plasma Ca concentrations in wk 1 to 8 after calving were affected by dietary P level in the dry period and in the lactation period, but no interaction between both was present. Feeding Dry-LP instead of Dry-HP diets resulted in 4.1% greater plasma Ca values, and feeding Lac-LP instead of Lac-HP diets resulted in 4.0% greater plasma Ca values. After calving, plasma inorganic phosphate (Pi) concentrations were affected by a 3-way interaction between sampling day after calving, and dietary P levels during the dry period and lactation. From d 1 to d 7 postpartum, cows fed Lac-HP had increased plasma Pi concentrations, and the rate appeared to be greater in cows fed Dry-LP versus Dry-HP. In contrast, plasma Pi concentrations decreased from d 1 to d 7 postpartum in cows fed Lac-LP, and this decrease was at a higher rate for cows fed Dry-HP versus Dry-LP. After d 7, plasma Pi concentrations remained rather constant at 1.5 to 1.6 mM when cows received Lac-HP, whereas with Lac-LP plasma Pi concentrations reached stable levels (i.e., 1.3–1.4 mM) at d 28 after calving. Milk production, DM intake, and milk concentrations of P, Ca, fat, protein, and lactose were not affected by any interaction nor the levels of dietary P. It is concluded that the feeding of diets containing 2.2 g of P/kg of DM during the last 6 wk of the dry period and 2.9 g of P/kg of DM during early lactation increased plasma Ca levels when compared with greater dietary P levels. These low-P diets may be instrumental in preventing hypocalcemia in periparturient cows and do not compromise DM intake and milk production. Current results suggest that P requirements in dairy cows during dry period and early lactation can be fine-tuned toward lower values than recommended by both the National Research Council and the Dutch Central Bureau for Livestock Feeding. Caution however is warranted to extrapolate current findings to entire lactations because long-term effects of feeding low-P diets containing 2.9 of g/kg of DM on production and health needs further investigation.     

Effect of feeding a negative dietary cation-anion difference diet for an extended time prepartum on postpartum serum and urine metabolites and performance

Forty-five multiparous Holstein cows and 15 springing Holstein heifers were used in a randomized block design trial to determine the effect of length of feeding a negative dietary anion-cation difference (DCAD) diet prepartum on serum and urine metabolites, dry matter (DM) intake, and milk yield and composition. After training to eat through Calan doors (American Calan Inc., Northwood, NH), cows within parity were assigned randomly to 1 of 3 treatments and fed a negative-DCAD diet for 3 (3W), 4 (4W), or 6 wk (6W) before predicted calving. Actual days cows were fed negative-DCAD diets was 19.2 ± 4.1, 27.9 ± 3.1, and 41.5 ± 4.1d for 3W, 4W, and 6W, respectively. Before the trial, all cows were fed a high-forage, low-energy diet. During the trial, cows were fed a diet formulated for late gestation (14.6% CP, 42.3% NDF, 20.5% starch, 7.1% ash, and 0.97% Ca) supplemented with Animate (Prince Agri Products Inc., Quincy, IL), with a resulting DCAD (Na + K − Cl − S) of −21.02 mEq/100 g of DM. After calving, cows were fed a diet formulated for early lactation (18.0% CP, 36.4% NDF, 24.2% starch, 8.1% ash, and 0.94% Ca) for the following 6 wk with a DCAD of 20.55 mEq/100 g of DM. Urine pH was not different among treatments before calving and averaged 6.36. No differences were observed in prepartum DM intake, which averaged 11.4, 11.5, and 11.7 kg/d for 3W, 4W, and 6W, respectively. Prepartum serum total protein, albumin, and Ca concentrations, and anion gap were within normal limits but decreased linearly with increasing time cows were fed a negative-DCAD diet. No differences were observed in serum metabolite concentrations on the day of calving. Postpartum, serum total protein and globulin concentrations increased linearly with increasing length of time the negative-DCAD diet was fed. No differences were observed in postpartum DM intake, milk yield, or concentration of fat or protein among treatments: 19.1 kg/d, 40.6 kg/d, 4.30%, and 2.80%; 19.6 kg/d, 41.5 kg/d, 4.50%, and 2.90%; and 18.6 kg/d, 41.0 kg/d, 4.30%, and 2.73% for 3W, 4W, and 6W, respectively. Results of this trial indicate that no differences existed in health or milk production or components in cows fed a negative-DCAD diet for up to 6 wk prepartum compared with those fed a negative-DCAD diet for 3 or 4 wk prepartum.     

The effect of cation-anion difference on calcium requirement, feed intake, body weight gain, and blood gasses and mineral concentrations of dairy calves

Our objective was to examine the effects of two diets with different cation-anion differences on Ca requirements in the growing calf. Holstein calves (n = 48, 24 males) were blocked at 56 to 70 d after birth (80+/-10 kg of body weight) according to sex and birth date and assigned randomly in a 2 x 3 factorial arrangement of dietary treatments containing cation-anion differences as meq (Na + K) - (Cl + S)/kg of diet dry matter and Ca content of 1) 0 and 0.35%, 2) 0 and 0.50%, 3) 0 and 0.65%, 4) 200 and 0.35%, 5) 200 and 0.50%, and 6) 200 and 0.65%. Feed intake and average daily gain did not differ among treatment groups. Plasma pH and Ca were unaffected by dietary Ca content or dietary cation-anion difference. Plasma Cl and P decreased linearly with increasing Ca content in the diet. Plasma HCO3 increased linearly with increased dietary Ca content. Plasma HCO3 and partial pressure of CO2 were higher in calves fed the 200 compared with calves fed the 0 cation-anion difference diets. Plasma Cl was, however, lower in calves fed the 200 compared with calves fed the 0 meq diets. An interaction of Ca content and dietary cation-anion difference was detected for plasma P content. Urinary pH increased linearly with increasing dietary Ca content. Calves fed the 200 meq dietary cation-anion difference had higher urinary pH values than those fed the 0 meq diet. Urinary P excretion was not altered by dietary cation-anion difference or Ca content of the diet. Calves fed the 0 meq diet had higher urinary cocnentrations of Ca and Cl when compared with those fed the 200 meq diet. Bone ash, P, Ca, Mg, and K content of the 10th rib were not affected by dietary treatments. Breaking strength of the seventh and ninth ribs increased quadratically with increasing dietary Ca content. Dietary cation-anion difference had no effect on the breaking strength of the seventh and ninth ribs. Varying the dietary cation-anion difference from 0 to 200 meq/kg of dietary dry matter had no effect on Ca requirement of the growing calf.     

Periparturient hypocalcemia in cows: prevention using intramuscular parathyroid hormone

Intravenously administered parathyroid hormone has recently been reported to prevent parturient paretic hypocalcemia in dairy cows. In the present study, Parathyroid hormone was administered intramuscularly prior to parturition to study its effects on Ca homeostasis and the incidence of periparturient hypocalcemia. Ten Holstein cows were fed a high Ca diet prepartum to predispose them to parturient paretic hypocalcemia. Five cows received intramuscular injections of synthetic bovine parathyroid hormone three times per day beginning about 6 d before parturition and continuing at a reduced dose for about 6 d after parturition. One of five control cows developed parturient paresis, and all five control cows exhibited hypocalcemia within 24 h of calving. None of the treated cows became paretic, and plasma calcium was normal or slightly elevated in these cows during the first 24 h after calving. Parathyroid hormone administration increased plasma concentrations of 1,25-dihydroxyvitamin D and hydroxyproline prior to parturition, suggesting that both intestinal Ca absorption and bone calcium resorption were increased by administration of the hormone. One hormone-treated cow became recumbent and required euthanasia. Although metastatic calcification of soft tissues was not observed, the death of this cow raises the possibility that there are unknown side effects of parathyroid hormone when administered intramuscularly.     

Use of 24-F-1,25-dihydroxyvitamin D3 to prevent parturient paresis in dairy cows

Forty-one aged Jersey cows were fed a high Ca diet prior to parturition to predispose them to parturient paresis. Twenty-one of the cows were treated with 24-F-1,25-dihydroxyvitamin D3, a synthetic analogue of 1,25-dihydroxyvitamin D3, 7 d before the expected parturition. Treated cows received either 100 micrograms (n = 7) or 150 micrograms (n = 14) of 24-F-1,25-dihydroxyvitamin D3, intramuscularly at 7-d intervals until the cow calved. Incidence of parturient paresis among untreated animals was 85% (17/20). Injections of 100 micrograms of 24-F-1,25-dihydroxyvitamin D3 reduced the incidence of parturient paresis to 43% (3/7), whereas 150 micrograms injections of 24-F-1,25-dihydroxyvitamin D3 reduced the incidence of parturient paresis to 29% (4/14). Plasma concentrations of hydroxyproline were not elevated prior to parturition in 24-F-1,25-dihydroxyvitamin D3-treated cows, indicating that treatment did not stimulate bone resorption and that the ability of 24-F-1,25-dihydroxyvitamin D3 to prevent parturient paresis likely resides in its ability to stimulate intestinal Ca absorption prior to parturition. Further, cows treated with 24-F-1,25-dihydroxyvitamin D3 that developed parturient paresis had lower than normal plasma concentrations of 1,25-dihydroxyvitamin D, indicating that 24-F-1,25-dihydroxyvitamin D3 treatment impairs the metabolism of 25-hydroxyvitamin D in response to hypocalcemia. These data suggest that injection of 24-F-1,25-dihydroxyvitamin D3, delivered at 7-d intervals prior to parturition, can effectively reduce incidence of parturient paresis in dairy cows.