Editor's note: The following article was originally published on the Pennsylvania State University Extension website, available here.
In the time period shortly before calving, large amounts of calcium are removed from the blood and are utilized in the mammary gland to be part of the colostrum. Calcium in colostrum may be eight to ten times greater than in the blood supply.
The rapid drop and the decreased mass of the calcium pool prior to parturition, and the failure of calcium absorption to increase fast enough after the onset of lactation, can predispose animals to milk fever or hypocalcemia.
There are other probable causes that have been associated with inducing milk fever. They include excessive bone formation due to elevated levels of gonadal hormones and rations containing excessive dietary levels of cations, especially potassium. In addition, other metabolic disorders can lead to clinical and subclinical hypocalcemia (i.e. ruminal stasis, displaced abomasum, retained placenta, prolapsed uterus, metritis, and ketosis). Figure 1 lists additional factors and situations.
Figure 1. Conditions associated with milk fever.
|Low calcium intake, especially for dry cows
(< .40% in total ration dry matter (TRDM))
|Heavy corn silage feeding; high moisture corn feeding;
inadequate supplementation; low grain intake (dry cows); low forage–high grain feeding.
|Low phophorus intake
(< .28% TRDM)
|Inadequate supplementation; high forage–low grain (i.e. pasturing dry cows).|
|Excessive calcium intake
(between .70% and 1.00% TRDM)
|High legume intake by dry cows; over supplementation with calcium.|
|Excessive phosphorus intake
(> .40% TRDM)
|Over supplementation; excessive grain feeding.|
|Excessive vitamin D intake
(> 100,000 units per head daily)
|Over supplementation can lead to calcification of tissues and result in heart failure.|
|Low magnesium intake
(< .20% in TRDM)
|Failure to balance low magnesium forages, i.e. corn silage, grasses, and small grains.|
|High potassium intake as it affects anion-cation balance (> 1.2% in TDRM)||Forages high in potassium content - over 1.5% on a dry matter basis.|
|Reduced mineral absorption; rumen pH over 6.8-7.2; higher incidence with increasing age (lack of vitamin D, alimentary tract stasis, lack of motility, constipation||High legume ration; high pH water over 8.5; under 3 to 5 pounds of grain intake; underfeeding forage or effective fiber; excessive protein intake.|
|Selenium or vitamin E deficiency
(< .10 ppm) (< 250 units per head daily)
|White muscle disease; lack of supplementation.|
|Toxemia||Coliform mastitis, other toxin-forming organisms; lower gastrointestinal tract stasis; reproductive tract infections.|
|Nerve or muscle damage||Injury at calving; damage from going down or lying on limbs for a prolonged time period.|