Short communication: Relationship between methods for measurement of serum electrolytes and the relationship between ionized and total calcium and neutrophil oxidative burst activity in early postpartum dairy cows

Intramammary lipopolysaccharide challenge in early- versus mid-lactation dairy cattle: Immune, production, and metabolic responses

Study objectives were to compare the immune response, metabolism, and production following intramammary LPS (IMM LPS) administration in early and mid-lactation cows. Early (E-LPS; n = 11; 20 ± 4 DIM) and mid- (M-LPS; n = 10; 155 ± 40 DIM) lactation cows were enrolled in an experiment consisting of 2 periods (P). During P1 (5 d) cows were fed ad libitum and baseline data were collected, including liver and muscle biopsies. At the beginning of P2 (3 d) cows received 10 mL of sterile saline containing 10 µg of LPS from Escherichia coli O111:B4/mL into the left rear quarter of the mammary gland, and liver and muscle biopsies were collected at 12 h after LPS. Tissues were analyzed for metabolic flexibility, which measures substrate switching capacity from pyruvic acid to palmitic acid oxidation. Data were analyzed with the MIXED procedure in SAS 9.4. Rectal temperature was assessed hourly for the first 12 h after LPS and every 6 h thereafter for the remainder of P2. All cows developed a febrile response following LPS, but E-LPS had a more intense fever than M-LPS cows (0.7°C at 5 h after LPS). Blood samples were collected at 0, 3, 6, 9, 12, 24, 36, 48, and 72 h after LPS for analysis of systemic inflammation and metabolism parameters. Total serum Ca decreased after LPS (26% at 6 h nadir) but did not differ by lactation stage (LS). Circulating neutrophils decreased, then increased after LPS in both LS, but E-LPS had exaggerated neutrophilia (56% from 12 to 48 h) compared with M-LPS. Haptoglobin increased after LPS (15-fold) but did not differ by LS. Many circulating cytokines were increased after LPS, and IL-6, IL-10, TNF-α, MCP-1, and IP-10 were further augmented in E-LPS compared with M-LPS cows. Relative to P1, all cows had reduced milk yield (26%) and DMI (14%) on d 1 that did not differ by LS. Somatic cell score increased rapidly in response to LPS regardless of LS and gradually decreased from 18 h onwards. Milk component yields decreased after LPS. However, E-LPS had increased fat (11%) and tended to have increased lactose (8%) yield compared with M-LPS cows throughout P2. Circulating glucose was not affected by LPS. Nonesterified fatty acids (NEFA) decreased in E-LPS (29%) but not M-LPS cows. β-Hydroxybutyrate slightly increased (14%) over time after LPS regardless of LS. Insulin increased after LPS in all cows, but E-LPS had blunted hyperinsulinemia (52%) compared with M-LPS cows. Blood urea nitrogen increased after LPS, and the relative change in BUN was elevated in E-LPS cows compared with M-LPS cows (36% and 13%, respectively, from 9 to 24 h). During P1, metabolic flexibility was increased in liver and muscle in early lactating cows compared with mid-lactation cows, but 12 h after LPS, metabolic flexibility was reduced and did not differ by LS. In conclusion, IMM LPS caused severe immune activation, and E-LPS cows had a more intense inflammatory response compared with M-LPS cows, but the effects on milk synthesis was similar between LS. Some parameters of the E-LPS metabolic profile suggest continuation of metabolic adjustments associated with early lactation to support both a robust immune system and milk synthesis.

Effects of feeding difructose anhydride on the mineral status and milking performance of transition cows

The objective of this study was to assess the potential effect of difructose anhydride III (DFAIII) on calcemia, magnesemia, and milking performance in dairy cows. A total of 66 multiparous Holstein cows in late pregnancy (gestation days, mean ± SD = 253.8 ± 2.13 d) were blocked according to their expected calving date and randomly assigned to either receiving no supplementation (control) or receiving 40 g/d of DFAIII (DFA) between -14 and +7 d relative to calving following a complete randomized block design. Cows in the control group received 640 g/d of a pellet containing no DFAIII, whereas DFA cows received the same pellet but containing 6.25% DFAIII. Pellets of each treatment were top-dressed on a daily basis while cows were dry and were fed via an automatic feeding system twice daily (320 g each feeding) during milking. Dry cows were fed once a day, whereas lactating cows were fed twice daily. Dry matter intake was individually monitored on a daily basis. Cows were milked twice daily and milk production and milk protein and fat contents recorded at every milking. Cows were kept on the study until they reached 21 d postpartum. Cows were weighed at dry-off (∼45 d before study enrollment) and twice daily after calving at the exit of the milking parlor. Cows were blood sampled for subsequent determination of serum Ca and Mg concentrations 3 d before the expected calving date and at 6, 12, 24, and 48 h and 7 and 14 d after calving. We found no differences in DMI before calving, but DFA cows consumed more feed than control cows at ∼15 DIM. All cows lost BW after calving, but DFA cows lost slightly less BW during the first 5 DIM than control cows. Cows on DFAIII produced more milk at ∼10 DIM compared with control cows, and DFAIII cows produced more milk protein than control cows 3 d after calving. Serum Ca concentrations were not affected by DFAIII supplementation; however, serum Mg concentrations at 6, 12, and 24 h after calving were greater in DFA than in control cows. In all, DFAIII did not affect postpartum calcemia but improved magnesemia between 6 and 24 h after calving. Milk production in DFA cows was improved around 10 d after calving and milk protein yield after 3 d postpartum compared with control cows. The mechanism leading to increased Mg availability is not clear and warrants further research.

Preoperative and Surgical Predictors of the Treatment Outcome of Dairy Cows with Right Abomasal Displacement-A Retrospective Study of 234 Cases

The displacement of the abomasum to the right (RDA) is a common condition regularly encountered in dairy cows, which requires urgent surgical correction. The survival of the patient primarily depends on early diagnosis and timely treatment, but other factors contributing to the outcome have been discussed in the literature. The objective of this study was to identify preoperative clinical, hematological, as well as intraoperative parameters that are associated with the prognosis of cows with RDA or abomasal volvulus (AV). This retrospective study included patients admitted to a veterinary teaching hospital over a period of 6 years with a diagnosis of RDA or AV. A total of 234 cows were included, of which 193 were discharged after treatment and thus classified as survivors. In contrast, 41 cases died or were euthanized during or after surgery and were categorized as non-survivors. Non-survivors showed more severe dehydration, higher heart rate, lower sodium, as well as higher L-lactate and phosphorus concentration in their blood prior to surgery compared with the survivors. During surgery, the abomasum of non-survivors was markedly dilated and twisted more frequently than in survivors. The results presented here can facilitate the early identification of animals with poor prognosis requiring more intensive peri- and postoperative care.

Validation of a blood gas device for ionized calcium analysis in Holstein cows

BACKGROUND

Accurate analysis of ionized calcium (iCa) is critical for the detection of hypocalcemia or subclinical hypocalcemia. The Edan i15 Vet (EDAN) blood gas device has not been validated for iCa in dairy cows.

OBJECTIVES

We aimed to validate the EDAN blood gas device against the Gem Premier 3000 (GEM) analyzer by measuring iCa concentrations and evaluating the ability of these measurements, compared with serum total calcium (TCa) concentrations, to diagnose subclinical hypocalcemia.

METHODS

iCa concentrations were measured with the EDAN and GEM devices, and serum TCa concentrations were measured with a wet biochemistry method with blood from 125 lactating Holstein cows between calving to day 27 postpartum.

RESULTS

Bland-Altman plots showed a mean and total bias of 0.05 and 0.24 mmol/L for the EDAN device, respectively. The intercept did not include zero, but the slope included 1.0 in the Passing-Bablok regression. The sensitivity and specificity (Se/Sp) of the EDAN device were 93/94%, 93/90%, 91/93%, and 85/95% for iCa cut-off values of <1.00, 1.05, 1.10, and 1.15 mmol/L, respectively, as determined with the GEM device. The Se/Sp were 57/82% and 72/80% for EDAN and 57/80% and 72/79% for GEM at serum TCa cut-off points <2.15 and <2.00 mmol/L, respectively. The average iCa concentrations analyzed with the GEM and EDAN devices were 1.04 ± 0.18 and 1.09 ± 0.17, respectively.

CONCLUSIONS

The EDAN device did not have satisfactory agreement with GEM and could not be used interchangeably, but it had satisfactory Se/Sp to diagnose subclinical hypocalcemia compared with the GEM-derived iCa cut-off points. Serum TCa concentration cut-off values were not suitable for diagnosing subclinical hypocalcemia because of unsatisfactory Se/Sp compared with iCa concentrations analyzed by the GEM and EDAN devices. The iCa values analyzed using the EDAN and GEM devices were consistent with previously reported data.

Acidified diet is not effective in preventing hypocalcemia in dairy cows on French commercial farms

The objective of this study was to assess, in the context of typical dairy farms in western France, the preventive effects of prepartum diet acidification (AcD) and mineral intake during late gestation on the incidence of subclinical hypocalcemia (SHC) and subclinical hypophosphatemia (SHP) after calving. We conducted a longitudinal study that followed a cohort of 371 Holstein cows from 26 French dairy farms; of these, 235 cows (15 farms) were supplied with anionic salts during late gestation, and 136 cows (11 farms) were not. Blood samples were collected from 1 to 22 cows per farm (average of 14.3 cows per farm) between 24 and 48 h after calving. Total calcium and inorganic phosphorus concentrations in plasma were then quantified by inductively coupled plasma - optical emission spectrometry. The effects of AcD on the incidence of SHC and SHP were assessed using mixed linear models that evaluated the cow-level factors parity, milk yield index, and individual health events/treatments, and the farm-level factors diet calcium and magnesium content, dietary phosphorus intake, vitamin D supply, diet crude protein content, and duration of AcD, with farm as a random effect. Approximately 55% of cows were diagnosed with SHC (calcium &lt; 2.0 mmol/l, n = 203) and 37% with SHP (inorganic phosphorus &lt; 1.3 mmol/l, n=136). The first model confirmed earlier findings that the risk of SHC is higher with increased parity (P ≤ 0.0001) and revealed a higher risk associated with high milk yield (P = 0.0005), high phosphorus intake (40–60 g/cow per day, OR = 3.5; ≥ 60 g/cow per day, OR = 7.3; P = 0.0003) and high vitamin D supply (≥ 19950 IU/cow per day, OR = 3, P = 0.007). The second model highlighted a greater risk of SHP with increasing parity (P = 0.03) and showed trends for the preventive effects of AcD (OR = 0.4, P = 0.07) and moderate amounts of phosphorus in the diet (OR = 0.4, P = 0.10). Overall, our results do not support the effectiveness of AcD in preventing SHC or SHP under field conditions examined here, probably resulting from insufficient diet acidification.

Implementation of hypocalcaemia prevention programmes in commercial dairy herds: From theory to practice

Hypocalcaemia prevention programmes have been widely studied in experimental settings, but their feasibility has not been assessed under field conditions. The main objective of this study was to evaluate, in the context of small dairy farms in western France, whether and how dairy farmers implement prevention programmes and manage the feeding of dry cows to prevent hypocalcaemia. Seventy-nine commercial Holstein dairy farms in Brittany (France) were enrolled in a qualitative study in 2019. We conducted in-person interviews with the farmers to 1) understand the rationale behind the type and seasonality of prevention programmes they implemented and 2) assess how closely they followed common recommendations when implementing them. Most farmers (80 %) used at least one prevention programme, especially supplying a mineral mix formulated to meet the needs of dry cows in late gestation (53 %), acidifying the diet in late gestation (37 %), and supplying calcium at calving (oral or injectable form, 37 %). The use of programmes depended on whether the diet composition varied throughout the year. Among farmers who provided an acidified diet, 25 % did not supply a specific mineral mix to dry cows to ensure an adequate amount of P, Ca, and Mg, which could decrease the effectiveness of the acidification programme. A lack of reliability in feeding practices, such as not weighing feed or not delivering feed frequently enough, was identified for 61 % of contributing farms. Management practices could result in supplying an unsuitable amount of P, Ca, or Mg immediately before calving; for example, inappropriate batching practices around calving were identified for 22 % (cows) to 32 % (heifers) of farms. In addition, nearly all contributing farmers had no processes in place to monitor the effectiveness of the programmes implemented. Reasons for this overall lack of compliance should be explored.

Comparison of the bovine blood gas parameters produced with three types of portable blood gas analyzers

Background

A definite diagnosis should be made in the bovine practice field, however, it was difficult to perform laboratory analysis immediately. Currently, three types of portable blood gas analyzers are available in Korea.

Objectives

This study aimed to evaluate the correlations among these three analyzers.

Methods

Seventy-two plasma samples from Holstein-Friesian cows were used for blood gas analysis, and three instruments (EDAN i15 Vet, VETSCAN i-STAT, and EPOC) were operated simultaneously. Moreover, plasma calcium levels were compared between these portable analyzers and blood chemistry device, which is usually used in a laboratory environment. Pearson analysis was performed to confirm the correlation of each parameter produced with the three instruments and blood chemistry analyzer.

Results

As results, high correlation was observed in parameters of pH, pO₂, potassium ion, ionized calcium, and glucose (p < 0.001, r > 0.7). In addition, pCO₂ showed a moderate correlation among the three analyzers (p < 0.001, r > 0.5), and there was no correlation among all instruments for sodium ions. There was also a high correlation between ionized calcium from the three portable devices and total calcium from the biochemistry analyzer (p < 0.001, r > 0.9).

Conclusions

In conclusion, there was a high correlation between results from the three different blood gas analyzers used in the bovine clinical field in Korea. Thus, a consistent diagnosis can be made even with different equipment if the operator is aware of the strengths and weaknesses of each piece of equipment and operates it properly.

Changes in the Relationship between Ionized and Total Calcium in Clinically Healthy Dairy Cows in the Period around Calving

Simple Summary

Hypocalcemia is a widespread problem in dairy cows in the first days after calving, which increases the risk for secondary diseases. In practice, the measurement of total blood serum or plasma calcium is widely used to diagnose hypocalcemia. The present study demonstrates a high discrepancy between total and ionized calcium specifically around calving, suggesting that only ionized calcium provides an accurate indication of the animal’s calcium status during that period. We developed an optimized model for prediction of ionized calcium from total calcium, non-esterified fatty acids, beta-hydroxybutyric acid, cholesterol, and phosphorous. However, the precision of that model is still unsatisfactory.

Abstract

We aimed to establish a model for prediction of iCa from tCa, using multivariable regressions with diverse blood constituents. Blood was taken from 14 cows at days −2, 0, 2, 4, 7, and 14 relative to parturition. Cows were clinically healthy, and no hypocalcaemia prophylaxis and treatment were applied. Total calcium and further parameters were determined from frozen serum. Ionized calcium, blood gases, and electrolytes were determined from heparin-stabilized blood samples. Linear regression between iCa and tCa was estimated. Precision improved only slightly using a multivariable model. Best precision was achieved when estimating the iCa:tCa ratio from other blood constituents. To identify the reason behind the poorly predictive value of tCa for iCa, the relative changes of iCa and tCa around calving were calibrated to the respective values of day −2 (=100%) for each cow. An increase in the iCa:tCa ratio was observed from 0.43 at day −2 to 0.48 at day 0, followed by a gradual decrease towards 0.43 at day 7. We conclude that routine measurement of iCa should be implemented in the diagnosis of hypocalcaemia. An optimized estimate of iCa from tCa with non-esterified fatty acids (NEFA), beta-hydroxybutyric acid, cholesterol, and phosphorous as co-predictors is still poorly satisfying.

Validation of the bovine blood calcium checker as a rapid and simple measuring tool for the ionized calcium concentration in cattle

Point-of-care (POC) devices that veterinary practitioners can use to easily and rapidly measure blood ionized calcium (iCa) levels in cows immediately after withdrawing a blood sample on the dairy farm are needed. Aims of present studies was to compare the commercially available ion-selective electrode handheld iCa meter (bovine blood iCa checker) with the benchtop blood gas analyzer GEM premier 3500 and handheld analyzer i-STAT 1. Sixty-two paired-point whole blood samples were obtained from three cows with hypocalcemia experimentally induced by Na₂-EDTA infusion. Whole blood samples were also obtained from the 36 cows kept on a farm in field conditions. The results using the bovine blood iCa checker correlated with those using the GEM premier 3500 and i-STAT 1. Bovine blood iCa checker was “compatible” with the GEM premier 3500 and i-STAT 1 because the frequency of differences between the measurements within ± 20% of the mean were 100% (65/65, >75%) and 90.8% (59/65, >75%), respectively. In the field trial, the blood iCa concentration measured by the bovine blood Ca checker was significantly positively correlated with that measured by the i-STAT 1 portable analyzer. Bovine blood iCa checker was “compatible” with the i-STAT 1 because the frequency of differences between the measurements within ± 20% of the mean was 100% (36/36, >75%). Results from these findings, the bovine blood iCa checker may be applied as a simplified system to measure the iCa concentration in bovine whole blood.

Effects of oral calcium bolus supplementation on intracellular polymorphonuclear leukocyte calcium levels and functionality in primiparous and multiparous dairy cows

The objectives of this study were (1) to characterize Ca levels and polymorphonuclear leukocyte (PMN) function in primiparous and multiparous animals following oral Ca bolus supplementation, and (2) to determine differential responses of boluses containing a lower dose of Ca than traditionally used in primiparous animals on Ca levels and PMN function. Jersey × Holstein crossbred animals (n = 104) were enrolled within 24 h of parturition. All animals were blocked by time relative to calving and randomly assigned to treatment. The Ca boluses were composed of a mixture of Ca chloride, Ca sulfate, and Ca propionate. For objective 1, animals were assigned to control (CON; no Ca supplementation), or a series of 2 Ca boluses given 24 h apart for a total of 50 g of Ca. Objective 2 treatments included control (CON; no Ca supplementation), a series of 2 Ca boluses given 24 h apart containing 50 g of Ca, or a series of 2 Ca boluses given 24 h apart containing 25 g of Ca. Blood samples were collected on d 1 (<24 h), 2, 3, 5, and 7 relative to parturition. Total serum Ca, serum haptoglobin, PMN intracellular Ca, PMN intracellular Ca after stimulation with an environmental Escherichia coli, PMN L-selectin surface expression, and PMN phagocytic and oxidative burst activities were analyzed. For objective 1 a tendency was detected for a treatment difference on basal intracellular PMN Ca and a treatment difference on E. coli-stimulated intracellular PMN Ca. We detected a parity × DIM effect for PMN oxidative burst intensity. However, no other interactions or parity effects on other functional PMN variables were detectable. In primiparous animals, we found a treatment difference for E. coli-stimulated intracellular PMN Ca among animals given 50 g of Ca but no treatment difference on basal intracellular PMN Ca. The 50 g of Ca treatment increased both PMN phagocytosis and oxidative burst intensities. Supplementing animals with 50 g of oral Ca increased intracellular PMN Ca and influenced PMN function.

The effect of prepartum negative dietary cation-anion difference and serum calcium concentration on blood neutrophil function in the transition period of healthy dairy cows

Our objectives were to assess the effects of a diet with a negative dietary cation-anion difference (DCAD) before calving on phagocytosis (Pc) and oxidative burst (OB) function of circulating neutrophils, and to determine the associations of serum ionized (iCa) and total calcium (tCa) concentrations with Pc and OB in transition dairy cows. We hypothesized that multiparous cows fed a negative DCAD diet prepartum would have greater iCa and tCa, and thus improved Pc and OB. From 3 wk before expected parturition until calving, 38 healthy multiparous cows from 3 farms were assigned to negative DCAD treatment (TRT; -100 mEq/kg of diet dry matter; n = 21) or a control (CON; 95 mEq/kg of dry matter; n = 17) diet. Each farm was on one treatment or the other at a time, but all farms contributed cows to both groups. Urine pH was measured weekly and in TRT was 6.1 ± 0.8 with 80% of 50 samples <7 and 74% ≤ 6.5. Phagocytosis, OB, iCa, and tCa were measured at d -7, 1, and 4 relative to calving. Median fluorescence intensity for Pc (MFIP) and OB (MFIOB), and the shift of percentage of cells active for Pc (PPc) and OB (POB) were measured in isolated, stimulated neutrophils via flow cytometry. Outcomes were assessed with mixed linear regression models accounting for repeated measures. There were no differences between treatments in the 4 neutrophil function outcomes. Although MFIOB varied over time, there were no interactions of treatment with time for any outcome. Serum ionized and tCa did not differ between TRT and CON. The least squares means ± standard deviation for iCa were: d -7, 1.23 ± 0.12 vs. 1.21 ± 0.12; d 1, 1.07 ± 0.12 vs. 1.02 ± 0.12; d 4, 1.16 ± 0.12 vs. 1.17 ± 0.12 mmol/L for TRT and CON, respectively; and for tCa: d -7 2.39 ± 0.25 vs 2.44 ± 0.31; d 1, 2.01 ± 0.25 vs 1.97 ± 0.31; d 4, 2.33 ± 0.25 vs 2.32 ± 0.31 mmol/L, respectively. The proportion of blood samples with tCa <2.15mmol/L at d -7, 1 and 4 was 5, 76, and 13%, respectively, with no differences between TRT and CON. Correlations of iCa or tCa with each of the 4 polymorphonuclear leukocyte (PMN) function outcomes were weak (r < |0.3|). We did not observe the hypothesized differences in aspects of innate immunity in clinically healthy multiparous cows fed a negative DCAD. We underline that cows that experienced clinical disease were excluded from this study, which is important for interpretation of the results.

Changes in ionized calcium concentration in the blood of dairy cows with peracute coliform mastitis

We determined the clinical signs and blood ionized calcium (iCa) levels in dairy cows with peracute coliform mastitis (PCM). The clinical scores at the onset of the disease (day 0) and on day 2 and subsequent days were significantly (P<0.01) higher than those of healthy cows. We found a positive correlation (r=0.894, P<0.01) between iCa and total calcium (TCa) concentrations in the blood of healthy cows ; however there was no correlation from day 0 to day 3 in the blood of PCM cows. Multiple regression analysis revealed that the concentration of iCa was correlated with rectal temperature, hematocrit value, platelet count, and albumin level of PCM cows at the onset of disease (r= −0.804, r=0.6576, r=0.6182, r=0.284, P<0.01, respectively). There was no correlation between the TCa concentration and these parameters for PCM cows at day 0. Low blood iCa concentration at day 0 for PCM cows was related to symptoms of septic shock involving hypothermia, activation of the blood coagulation system, and dehydration.

On-farm use of a water hardness test kit to assess total blood calcium level in dairy cattle

In this Research Communication we report the measurement of total blood calcium concentration with a water hardness test kit (WHTK) in dairy cattle and compare the results to a reference method. The study was carried out on 107 Holstein Friesian cows from three commercial dairy farms in Sardinia (Italy). Blood samples were collected ≤7 d from calving and total serum calcium concentration was determined using a biochemical analyzer and a WHTK. The relationship between the laboratory results and the WHTK results was investigated using Spearman's rank correlation test and simple linear regression was determined. Sensitivity, specificity, negative and positive predictive values, intra and inter-assay coefficient of variation were also calculated. The test values were highly correlated with the laboratory values (R2 = 0.72, P < 0.001). Sensitivity and specificity were respectively 88 and 83% for the WHTK and intra and inter-assay coefficients of variation were 7.3 and 11.3% respectively. The WHTK was identified as a potential on-farm tool for monitoring early postpartum Ca concentrations at herd level.

Intravenous calcium infusion in a calving protocol disrupts calcium homeostasis compared with an oral calcium supplement

Hypocalcemia is a common postpartum condition in dairy cows, which negatively affects health and production. Intravenous Ca infusions are commonly included in calving protocols to prevent or mitigate the effect of hypocalcemia in multiparous cows. Thus, we sought to contrast the effect of intravenous Ca infusion against voluntary oral Ca intake on Ca metabolism. Serum total Ca (tCa) and whole-blood ionized Ca (iCa) were monitored in 24 multiparous Holstein cows after parturition. Precalving diets were formulated with a positive dietary cation-anion difference of 172 mEq/kg of DM and contained 4.1 g of Ca/kg of DM. At parturition, cows were blocked by calving sequence and calcemic status as either normocalcemic (cutoff threshold of iCa ≥1.10 mmol/L) or hypocalcemic (cutoff threshold of iCa <1.10 mmol/L). Cows in each block were randomly assigned to 1 of 2 treatments: either an oral source of Ca (Ca-Oral; n = 12) or an intravenous source of Ca (Ca-IV; n = 12). Cows in the Ca-Oral group were offered a 20-L commercial Ca suspension (48 g of Ca) for voluntary consumption. The supplement contained Ca carbonate, Ca formate, Ca propionate, and other minerals and vitamins (Farm-O-San Reviva, Trouw Nutrition, Amersfoort, the Netherlands). Cows in the Ca-IV group received a 450-mL intravenous Ca solution (13 g of Ca) that contained 298 mg/mL of Ca gluconate, 33 mg/mL of magnesium chloride, and 82 mg/mL of boric acid (AmosCAL, Kommer-Biopharm BV, Heiloo, the Netherlands). Both treatments were initiated within 25 ± 10 min after calving. The oral Ca suspension was offered to cows in a 25-L bucket and was available for 10 min. All cows in the Ca-Oral group voluntarily consumed the entire 20 L of the Ca suspension within 5 min. Blood samples for Ca analyses were collected at 0 (before treatment initiation), 1, 3, 10, and 18 h relative to treatment, and at 0700 and 1900 h for the next 2 consecutive days, to represent the 24-, 36-, 48-, and 60-h sampling time points. In Ca-IV cows, both iCa and tCa concentrations peaked at 1 h (1.54 mmol/L for iCa and 2.85 mmol/L for tCa) and declined to a nadir at 24 h following treatment initiation (0.94 mmol/L for iCa and 1.74 mmol/L for tCa). Although whole-blood iCa and serum tCa were higher at 1 and 3 h in Ca-IV cows, concentrations of iCa were greater for Ca-Oral cows at 18, 24, and 36 h and for tCa at 24 and 36 h. Our data indicate that intravenous Ca infusion immediately induced a state of hypercalcemia followed by lower whole-blood iCa and serum tCa concentrations 24 h later compared with oral Ca.

Effect of induced hypocalcemia in nonlactating, nonpregnant Holstein cows fed negative DCAD with low, medium, or high concentrations of calcium

The main objective of this study was to determine how feeding different dietary calcium (Ca) concentrations in combination with a negative dietary cation-anion difference (DCAD) would affect the cow's response to induced hypocalcemia. We conducted an experiment with multiparous, nonlactating, nonpregnant Holstein cows fed a negative DCAD (average -18.2 across all diets) for 21 d with low (LC; 0.45% Ca; n = 5), medium (MC; 1.13% Ca; n = 6), or high (HC; 2.02% Ca; n = 6) concentrations of dietary Ca. Urine and blood samples were collected and urine pH measured daily during the 21-d feeding period prior to hypocalcemia challenge. Cows were then subjected to a controlled induction of hypocalcemia to determine how dietary Ca intake affected the response to a hypocalcemia challenge. On days 22, 23, and 24, hypocalcemia was induced with an intravenous infusion of 5% EGTA in 2 different cows from each treatment daily. During infusion, blood samples were collected every 15 min until 60% of prechallenge ionized calcium (iCa) concentrations were achieved. Samples were collected postinfusion at 0, 2.5, 5, 10, 15, 30, and every 30 min thereafter until 90% of prechallenge iCa was reached. Blood pH, hematocrit, and serum total Ca (tCa), sodium (Na), potassium (K), phosphorous (P), magnesium (Mg), and serotonin did not differ (P > 0.05) among treatments during the feeding period. Blood iCa (P = 0.04) and glucose (P = 0.03) were significantly elevated in HC compared with LC and MC cows during the feeding period. Urine pH was less than 6.0 in all cows, but was lowest in LC (P = 0.02) compared with MC and HC cows during the feeding period. Urine Ca, P, Mg, and deoxypyridinoline did not differ among treatments (P > 0.05). Cows fed HC maintained higher concentrations of iCa (P = 0.03) during the challenge period than MC (P = 0.04), and LC (P = 0.004), and required a longer time to reach 60% of whole blood iCa, and required more EGTA to reach 60% iCa than MC or LC cows (P = 0.01). Serum tCa decreased in all cows during infusion (P < 0.0001) but did not differ among treatments. Serotonin concentrations were elevated in MC cows compared with HC and LC cows during EGTA infusion (P = 0.05), suggesting an interdependent relationship between iCa and serotonin. Cows fed HC had a slower rate of decrease in iCa, but not tCa, when induced with hypocalcemia, indicating potential metabolic benefits of feeding higher dietary Ca in combination with a negative DCAD.