No one knows the cause of milk fever, or hypocalcemia (as it's properly called). The following, however, is known:
Our college dairy herd — a combination of Holsteins and Ayrshires — is relatively high-production by Quebec (Canada) standards and has had its fair share of milk fever. Last year, however, we initiated a new feeding program that has proven 100 percent effective in preventing milk fever. Here's what we did:
We divided our animals into two equal groups. The first received the usual high-calcium feed prior to calving, while the second got five to seven pounds of low-calcium grain and hay per animal per day for the 10 to 14 days before delivery. (The latter diet provides 100 percent of the dry cow's energy, protein, and phosphorus needs, but only 60 percent of her calcium requirements.)
What we observed was that the animals in the "high-calcium" group went on to experience the usual incidence of milk fever after calving ... while every one of the cows that'd been on the low-calcium diet remained healthy.
Why did the cows in the "low-calcium" group fare better? We think that by depriving these cows of dietary calcium, we were able to lower their blood calcium levels slightly and — in turn — stimulate the animals' parathyroid glands. (These are the glands responsible for maintaining the proper level of calcium in the blood. When there is a high demand for calcium — as during lactation — these glands secrete a hormone that causes bone calcium to be liberated into the bloodstream.) Thus, when these cows freshened, their parathyroid glands were already active and working ... and their blood calcium levels remained normal.
The cows that got high-calcium rations before calvingon the other hand — never lacked for blood calcium, and their parathyroid glands — as a result — remained dormant up to (and through) delivery. The sudden demand for calcium brought on by lactation caught these animals' sleeping parathyroids by surprise. Blood calcium levels — meanwhile — plunged dangerously, and the cows developed milk fever.
If your dairy animals have been plagued by milk fever, you might want to give the low-calcium-diet idea a try. (It's certainly worked well for us.) Just remember two things:  The caws should go back on their normal diet after parturition, and  milk fever — when it occurs — is a matter of life and death. Should any of your animals come down with hypocalcernia, don't take chances ... call a veterinarian at once.
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