No one knows the cause of milk fever, or hypocalcemia (as it's properly called). The following, however, is known:
[1] The disease occurs primarily in high-milk-production cows that have calved once or twice before.
[2] The symptoms begin to appear-usually-within 72 hours after calving. (First, the afflicted animal shows signs of unsteadiness . . . then she collapses and lies with her head turned to one side, her eyes dull and expressionless. The name "milk fever" notwithstanding, the cow's temperature is usually below-not above-normal.)
[3] The physiological abnormality most consistently associated with the disease is low blood calcium.
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% 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% of the dry cow's energy, protein, and phosphorus needs, but only 60% 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: [1] The caws should go back on their normal diet after parturition, and [2] 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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