title: Influence of feeding a low-phosphorus diet on leucocyte function in dairy cows.
abstract: Phosphorus depletion and hypophosphatemia have been described to interfere with immune function in rats and humans. In dairy cows, hypophosphatemia has been associated with muscle weakness and recumbency as well as with intravascular hemolysis resulting from increased osmotic fragility of erythrocytes, but so far, the influence of P depletion and hypophosphatemia on immune function has not been studied. Therefore, the aim of this study was to investigate whether P depletion and ensuing hypophosphatemia are associated with impaired granulocyte and lymphocyte function. Eight mid-lactation dairy cows were fed a P-deficient ration (0.2% P/kg of DM) for a period of 4wk. The depletion phase was preceded by a 2-wk acclimatization period and followed by a 2-wk repletion phase, during which the same ration was supplemented with P to meet or exceed daily requirements. Blood samples were collected at the end of the acclimatization period, after 2 and 4wk of P depletion, and at the end of the repletion phase. Plasma phosphate concentrations ([Pi]) were determined and white blood cells were counted and isolated. General immune function was investigated by performing a phagocytosis assay with Staphylococcus aureus and a lymphocyte stimulation test (LST) with concanavalin A and pokeweed mitogen. The plasma [Pi] decreased significantly, with the lowest values (mean 0.7±0.2mmol/L) occurring after 2wk of depletion, although depletion was continued for another 2wk. During repletion, plasma [Pi] increased above baseline concentrations. Granulocyte counts changed in parallel with plasma [Pi] over time, decreasing significantly at 2wk after P depletion and increasing again thereafter. Granulocyte survival after phagocytosis was lowest after 4wk of P depletion. Phagocytosis activity of surviving granulocytes determined by mean fluorescence intensity was higher, indicating that phagocytosis was not negatively influenced by P depletion. Lymphocyte stimulation showed a similar trend, with a decreasing stimulation index at the end of P depletion, but differences were not statistically significant. Data presented in this study indicate that hypophosphatemia leads to a decrease in granulocyte counts. Chronic P depletion impairs granulocyte survival during phagocytosis but not phagocytosis activity. Lymphocyte function is not influenced by P depletion.
authors: Department of Farm Animal Health, Faculty of Veterinary Medicine, NL-3584CL Utrecht, the Netherlands. Electronic address: s.w.f.eisenberg@uu.nl.
authors: S W F
authors: SW
authors: Eisenberg
authors: Department of Farm Animal Health, Faculty of Veterinary Medicine, NL-3584CL Utrecht, the Netherlands.
authors: L
authors: L
authors: Ravesloot
authors: Department of Farm Animal Health, Faculty of Veterinary Medicine, NL-3584CL Utrecht, the Netherlands; Division of Immunology, Department of Infectious Disease and Immunology, Faculty of Veterinary Medicine, NL-3584CL Utrecht, the Netherlands.
authors: A P
authors: AP
authors: Koets
authors: Department of Farm Animal Health, Faculty of Veterinary Medicine, NL-3584CL Utrecht, the Netherlands.
authors: W
authors: W
authors: Grünberg
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet / Q000662:veterinary*; D019587:Dietary Supplements; D005260:Female; D017674:Hypophosphatemia / Q000662:veterinary*; D007774:Lactation; D007958:Leukocyte Count / Q000662:veterinary; D007962:Leukocytes / Q000502:physiology*; D008213:Lymphocyte Activation; D010587:Phagocytosis; D010758:Phosphorus / Q000008:administration & dosage / Q000097:blood*; D051381:Rats; D013211:Staphylococcus aureus / Q000502:physiology
chemical_list: D010758:Phosphorus
keywords: dairy cow; hypophosphatemia; leucocyte function; phosphorus depletion