Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 1995
Publication Date: N/A
Interpretive Summary: Milk fever is a disease of low blood calcium concentration associated with calving and milk production in dairy cows. It affects 6-8% of all dairy cows each year. Milk fever occurs because calcium is removed from the bloodstream to make high calcium milk faster than it can be replaced from the diet or bone stores. The result is a severe decline in blood calcium concentrations. One factor thought to be important in susceptibility to milk fever is the level of receptors that recognize the calcium regulating hormone, 1,25-dihydroxyvitamin D, present in the intestine. We measured vitamin D receptor concentration in cows before and after calving and found that the receptor concentration decreases in all cows at calving, but could not detect a significant difference between cows that went on to develop milk fever and those that did not. This decline in vitamin D receptor concentration at calving may aggravate the cow's ability to maintain normal blood calcium concentration, but is not the major factor causing milk fever.
Technical Abstract: Milk fever is the clinical disease associated with severe hypocalcemia in dairy cows. In this paper, we test the hypothesis that calcium homeostasis is compromised as a result of a reduced concentration of receptors for 1,25-dihydroxyvitamin D in the tissues of cows that develop milk fever. Samples of colon mucosa were obtained for analysis of vitamin D receptor concentration in a longitudinal study of Jersey cows during the 2 wk before and after parturition. In the first study, 21 cows fed an alfalfa hay diet were biopsied every 3rd d during the periparturient period. Colon vitamin D receptor concentration in late gestation was 3- to 4-fold higher than the concentration of colon mucosa vitamin D receptor concentration in non-pregnant cows (90 +/- 8 versus 26 +/- 5 femtomoles/mg protein). At parturition, colon vitamin D receptor concentrations decreased to 66 +/- 7.5 femtomoles/mg protein. During early lactation, colon vitamin D receptor concentrations were similar to pre-calving concentrations. There was no significant difference in colon vitamin D receptor concentration prior to calving, at calving, or in early lactation in cows that did and did not develop milk fever. Similar results were obtained in a second study, where seven cows were fed a high cation alfalfa diet and six cows were fed the same diet with anionic salts added.