Feeding before that calf arrives.
The wrong diet can risk milk fever at calving.
Milk fever (aka hypocalcemia) is a disease that occurs mainly in cows around calving when a cow has to abruptly change its metabolism at the end of the dry (non-lactating) period to a high performance lactation phase. Milk fever is caused by an insufficient amount of calcium in the blood and particularly affects cows with a high milk yield.
During their dry (non-lactating) period, cows have a relatively low need for calcium. When lactation starts, the need for calcium suddenly almost doubles, as large amounts of calcium are required for the production of colostrum. Calcium is generally supplied from feed but when that is insufficient to meet the demand then needed calcium is drawn from their bones. When the supply from the feed and bones is insufficient the body draws the missing calcium from the muscles. This ultimately leads to symptoms of paralysis and overstimulation of the nervous system which is what we call milk fever.
Now… you might conclude that simply increasing the amount of calcium in your Dexter cows diet pre-calving is any easy way to preventing milk fever at calving, but it is exactly the opposite.
Feeding too high a calcium diet (alfalafa, clover, peanut or soybean and especially lush spring grass) will prevent her from maximizing the available calcium when she needs it most – at calving time.
It’s a bit counter-intuitive. You would think if a cow is lacking enough calcium to accommodate the big demand needed right at calving – then the solution would be to provide more calcium rich feed, but according to Jennifer Mather DVM, Bear River Mobile Vet Services in northern CA, a cows body (metabolism) must be accustomed/trained/ready to draw on the reserves of calcium in their bones. If all the calcium needs of a cow are continually being met (or even exceeded) by feed intake, their bodies/metabolism adapt, and become inefficient at drawing calcium from the stores in their bones. So when that big abrupt calcium demand comes at calving… their body first uses any nutritional calcium available, then tries to draw from the bones. When neither of those supply the need quickly enough the last source of calcium is the muscles.
Dexters have an inheritance of centuries of neglect, running semi-wild in the hills of Ireland, sustaining on browse where most other bovine breeds would struggle.
This is important to remember. We risk messing things up when we do not respect their innate hardiness and coddle them with rich feed (aka high quality) thinking we are being a responsible herdsman and doing them a good deed.
It’s a natural assumption to think that a cow requires more “nutrition” when she is pregnant and “eating for two” but nothing could be more false. The very best thing we can do for our Dexter cows and heifers is keep them on a simple diet of mature grass (not new green grass) or grass hay and provide access to minerals – that’s it. Their diet needs to leave them on the thinner side rather than the heftier side. Not only will this greatly reduce the chances of milk fever, it will also increase their fertility.
