The effect of transient, moderate dietary phosphorus deprivation on phosphorus metabolism, muscle content of different phosphorus-containing compounds, and muscle function in dairy cows

Abstract

Hypophosphatemia is a common finding in periparturient and anorectic cattle. Although the clinical relevance of hypophosphatemia in cattle is uncertain, it has been empirically associated with persistent recumbency, specifically in periparturient dairy cows. The objective of the present study was to determine if transient dietary phosphorus (P) deprivation over a course of 5 wk, by feeding an approximately 40% P-deficient ration to lactating dairy cows, would result in altered muscle function or muscle P metabolism severe enough to present a risk for animal health and well-being. In addition, we wanted to determine the association between the plasma phosphate concentration ([Pi]) and muscle tissue P content to assess to what extent intracellular P deprivation of muscle cells could be extrapolated from subnormal plasma [Pi]. Ten healthy multiparous, mid-lactating dairy cows received a ration with a P content of 0.18% over a period of 5 wk. Following the P-deprivation phase, the same ration supplemented with P to obtain a dietary P content of 0.43% was fed for 2 wk. Blood and urine samples were collected regularly and muscle biopsies were obtained repeatedly to determine the P content in muscle tissue. Function of skeletal and heart muscles was evaluated by electrocardiography and electromyography conducted repeatedly throughout the study. Feeding the P-deficient ration resulted in the rapid development of marked hypophosphatemia. The lowest plasma [Pi] were measured after 9 d of P depletion and were, on average, 60% below predepletion values. Plasma [Pi] increased thereafter, despite ongoing dietary P depletion. None of the animals developed clinical signs commonly associated with hypophosphatemia or any other health issues. Urine analysis revealed increasing renal calcium, pyridinoline, and hydroxypyridinoline excretion with ongoing P deprivation. Biochemical muscle tissue analysis showed that dietary P depletion and hypophosphatemia were not associated with a decline in muscle tissue P content. Electromyographic examination revealed increased occurrence of pathological spontaneous activity in striated muscles after 2 wk of dietary P depletion in several cows, which could be suggestive of neuromuscular membrane instability. No effect on heart muscle activity was identified electrocardiographically. These results suggest that counter-regulatory mechanisms were sufficient to maintain normal muscle tissue P content during transient and moderate P deprivation. Muscle function was not grossly affected, although the increased occurrence of pathological spontaneous activity suggests that subclinical neuropathy or myopathy, or both, may have occurred with ongoing P deprivation. The results presented here indicate that plasma [Pi] is unsuitable for assessing muscle tissue P content in cattle.

Concentration of Potassium in Plasma, Erythrocytes, and Muscle Tissue in Cows with Decreased Feed Intake and Gastrointestinal Ileus

“…Then an approximately 200 mg muscle biopsy specimen was obtained using the biopsy needle7, put into the sample vial9 which was tightly closed and analyzed for tissue potassium (IDEXX laboratories Germany). Biopsy specimens were kept at room temperature until analyzed similar to studies which have been published recently 18, 19, 20. The analysis was performed within 48 hours of sample collection.…”

“…The potassium measurement in blood plasma was performed at the laboratory of the clinics for ruminants using an ISE incorporated in a blood gas analysis device 5. The potassium concentration in tissue and in the erythrocytes were measured by one of the authors (Dr. Anja Müller, Vet Med Labor GmhH, Division of IDEXX Laboratories, Germany) using inductively coupled plasma optical emission spectroscopy (ICP‐OES)13 which has been described previously 18, 19, 20. Dr. Müller was blinded to the origin of the samples.…”

“…e The potassium concentration in tissue and in the erythrocytes were measured by one of the authors (Dr. Anja M€ uller, Vet Med Labor GmhH, Division of IDEXX Laboratories, Germany) using inductively coupled plasma optical emission spectroscopy (ICP-OES) m which has been described previously. [18][19][20] Dr. M€ uller was blinded to the origin of the samples. For the measurements of intracellular potassium concentration in erythrocytes, 1 mL of the heparinized blood was mixed with physiologic NaCl solution and centrifuged.…”

Phosphorus content of muscle tissue and muscle function in dairy cows fed a phosphorus-deficient diet during the transition period

“…Attempts to experimentally induce hypophosphatemic recumbency in cattle have been unsuccessful thus far, and reports about treatment efficacy of oral or parenteral P supplementation in cattle with presumed 4073 hypophosphatemic recumbency are inconsistent at best (Rodehutscord et al, 1994;Grünberg, 2014;Puggaard et al, 2014;Grünberg et al, 2015b). A potential mechanism through which P depletion or hypophosphatemia may result in disturbed muscle function has not been unraveled, but depletion of energy stores in muscle tissue in states of P deficiency has been proposed in combination with membrane instability (Grünberg, 2014;Grünberg et al, 2015b). Muscle fibers depend on the availability of creatine phosphate (CPh) and adenosine phosphates as a source of energy, and it is thought that hypophosphatemia is indicative of P deficiency and thus is accompanied by depletion of intracellular P stores.…”

“…Electromyographic examinations were conducted at the time points T 1 , T 2 , T 3 , T 4 , and, for cows of replicate 1, T 5 . Electromyographies were always conducted and analyzed by the same investigator as described in earlier studies (Wijnberg et al, 2004;Grünberg et al, 2015b). Briefly, the electrical activity of intercostal (IC) and biceps femoris (BF) muscles was determined to evaluate pathologic spontaneous activity and to assess the properties of isolated MUAP and interference patterns (Liguori et al, 1997).…”