title: Effect of induced subclinical hypocalcemia on physiological responses and neutrophil function in dairy cows.
abstract: The objectives were to study the effects of induced subclinical hypocalcemia [SCH, blood ionized Ca (iCa(2+)) <1.0mM, without recumbency] on physiological responses and function of immune cells in dairy cows. Ten nonpregnant, nonlactating Holstein cows were blocked by lactation and assigned randomly to a normocalcemic (NC; intravenous infusion of 0.9% NaCl i.v. plus 43 g of oral Ca, as Ca sulfate and Ca chloride, at -1 and 11h) or an induced SCH [SCHI, 5% ethylene glycol tetraacetic acid (EGTA), a selective iCa(2+) chelator, intravenous infusion] treatment for 24h, using a crossover design. The sequence of treatments was either NC-SCHI or SCHI-NC, with a 6-d washout period. Ionized Ca was evaluated before, hourly during the infusion period, and at 48 and 72 h, to monitor concentrations and adjust the rate of infusion, maintaining blood iCa(2+) <1.0mM in SCHI throughout the 24-h infusion period. Additional measurements included heart and respiratory rates, rectal temperature, dry matter intake, rumen contractions, whole-blood pH, concentrations of glucose and K in whole blood, concentrations of total Ca, Mg, nonesterified fatty acids, β-hydroxybutyrate, and insulin in plasma, and urinary excretion of Ca. Total and differential leukocyte count in blood was also performed. The concentration of cytosolic iCa(2+) in neutrophils and lymphocytes was quantified and neutrophil function was assayed in vitro. Infusion of a 5% EGTA solution successfully induced SCH in all SCHI cows, resulting in decreased blood iCa(2+) concentrations throughout the 24-h treatment period (0.77 ± 0.01 vs. 1.26 ± 0.01 mM iCa(2+)). Induction of SCH reduced dry matter intake on the day of infusion (5.3 ± 0.8 vs. 9.1 ± 0.8 kg/d) and rumen contractions (1.9 ± 0.2 vs. 2.7 ± 0.2 contractions/2 min) for the last 12h of infusion. Cows in SCHI had decreased plasma insulin concentration (1.44 ± 0.23 vs. 2.32 ± 0.23 ng/mL) evident between 6 and 18 h after the beginning of the infusion, accompanied by increased concentrations of glucose (4.40 ± 0.04 vs. 4.17 ± 0.04 mM). Plasma nonesterified fatty acids concentration was greater for SCHI than NC cows (0.110 ± 0.019 vs. 0.061 ± 0.014 mM). Neutrophils of cows in SCHI had a faster decrease in cytosolic iCa(2+) after stimulation with ionomycin (9.9 ± 1.0 vs. 13.6 ± 1.4 Fluo-4:Fura Red post-end ratio) in vitro. Furthermore, induction of SCH reduced the percentage of neutrophils undergoing phagocytosis (22.1 ± 2.1 vs. 29.3 ± 2.1%) and reduced the oxidative burst response after incubation of pathogenic bacteria (16.1 ± 1.7 vs. 24.2 ± 1.7%). Subclinical hypocalcemia compromised appetite, altered metabolism, and impaired function of immune cells in dairy cows.
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611.
authors.forename: N
authors.initials: N
authors.lastname: Martinez
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611.
authors.forename: L D P
authors.initials: LD
authors.lastname: Sinedino
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611.
authors.forename: R S
authors.initials: RS
authors.lastname: Bisinotto
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611.
authors.forename: E S
authors.initials: ES
authors.lastname: Ribeiro
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611.
authors.forename: G C
authors.initials: GC
authors.lastname: Gomes
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611.
authors.forename: F S
authors.initials: FS
authors.lastname: Lima
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611.
authors.forename: L F
authors.initials: LF
authors.lastname: Greco
authors.affiliation: Department of Large Animal Clinical Sciences, and University of Florida, Gainesville 32611.
authors.forename: C A
authors.initials: CA
authors.lastname: Risco
authors.affiliation: Department of Large Animal Clinical Sciences, and University of Florida, Gainesville 32611.
authors.forename: K N
authors.initials: KN
authors.lastname: Galvão
authors.affiliation: School of Natural Resources and Environment, University of Florida, Gainesville 32611.
authors.forename: D
authors.initials: D
authors.lastname: Taylor-Rodriguez
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611.
authors.forename: J P
authors.initials: JP
authors.lastname: Driver
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611.
authors.forename: W W
authors.initials: WW
authors.lastname: Thatcher
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611. Electronic address: jepsantos@ufl.edu.
authors.forename: J E P
authors.initials: JE
authors.lastname: Santos
mesh_terms: D020155:3-Hydroxybutyric Acid / Q000097:blood; D000818:Animals; D001786:Blood Glucose; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D005947:Glucose / Q000378:metabolism; D006996:Hypocalcemia / Q000378:metabolism*; D007328:Insulin / Q000097:blood; D007774:Lactation / Q000502:physiology; D009504:Neutrophils / Q000502:physiology*; D010587:Phagocytosis / Q000187:drug effects; D011897:Random Allocation; D016897:Respiratory Burst; D012417:Rumen / Q000378:metabolism
chemical_list: D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D005947:Glucose; D002118:Calcium; D020155:3-Hydroxybutyric Acid
keywords: dairy cow; immune function; metabolism; subclinical hypocalcemia