title: Diet-induced pseudohypoparathyroidism: A hypocalcemia and milk fever risk factor.
abstract: Subclinical hypocalcemia may affect half of all multiparous cows, and clinical hypocalcemia or milk fever affects approximately 5% of dairy cows each year. This disorder of calcium homeostasis can be induced by several dietary factors. Recent studies implicate high dietary potassium and high dietary cation-anion difference (DCAD) with increased risk of milk fever. The hypothesis tested in this study was that high-DCAD diets fed to prepartum cows reduce tissue sensitivity to parathyroid hormone (PTH), inducing a pseudohypoparathyroid state that diminishes calcium homeostatic responses. Multiparous Jersey cows were fed low- or high-DCAD diets in late gestation, creating a compensated metabolic alkalosis in the high-DCAD cows and a compensated metabolic acidosis in the low-DCAD cows. They then received synthetic PTH injections at 3-h intervals for 48 h. Parathyroid hormone is expected to cause an increase in plasma calcium by increasing renal production of 1,25-dihydroxyvitamin D and increasing bone calcium resorption. Plasma calcium concentration increased at a significantly lower rate in cows fed the high-DCAD diet. Cows fed the high-DCAD diet also produced significantly less 1,25-dihydroxyvitamin D in response to the PTH injections than cows fed the low-DCAD diet. Serum concentrations of the bone resorption marker carboxyterminal telopeptide of type I collagen were numerically lower in cows fed the high-DCAD diet but this difference was not statistically significant. These data provide direct evidence that high-DCAD diets reduce tissue sensitivity to PTH. The metabolic alkalosis associated with high-DCAD diets likely induces a state of pseudohypoparathyroidism in some dairy cows at the onset of lactation, resulting in hypocalcemia and milk fever.
authors.affiliation: Periparturient Diseases of Cattle Research Unit, National Animal Disease Center, US Department of Agriculture-Agricultural Research Service, Ames, IA 50010. Electronic address: jpgoff@iastate.edu.
authors.forename: J P
authors.initials: JP
authors.lastname: Goff
authors.affiliation: Institute of Animal Nutrition, Vetsuisse Faculty University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Liesegang
authors.affiliation: Periparturient Diseases of Cattle Research Unit, National Animal Disease Center, US Department of Agriculture-Agricultural Research Service, Ames, IA 50010.
authors.forename: R L
authors.initials: RL
authors.lastname: Horst
mesh_terms: D000818:Animals; D002118:Calcium / Q000097:blood / Q000652:urine; D056657:Cathepsin K / Q000378:metabolism; D002417:Cattle; D002418:Cattle Diseases / Q000097:blood* / Q000209:etiology / Q000473:pathology; D003404:Creatinine / Q000652:urine; D004032:Diet / Q000009:adverse effects* / Q000662:veterinary*; D005260:Female; D006996:Hypocalcemia / Q000209:etiology / Q000662:veterinary*; D007774:Lactation; D008274:Magnesium / Q000097:blood / Q000652:urine; D010281:Parathyroid Hormone / Q000008:administration & dosage / Q000097:blood; D010319:Parturient Paresis / Q000097:blood / Q000209:etiology / Q000473:pathology*; D011247:Pregnancy; D011547:Pseudohypoparathyroidism / Q000209:etiology / Q000662:veterinary*; D012307:Risk Factors; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; D003404:Creatinine; D056657:Cathepsin K; D008274:Magnesium; D002118:Calcium
keywords: dietary cation-anion difference; milk fever; pseudohypoparathyroid