before calving: what to feed

Another farmer question:

Hi! We just obtained our first dairy heifers and are about to breed them. I recently read or heard somewhere that feeding a dry cow alfalfa hay before she calves is not a good idea because it has too much calcium in it and can, ironically, lead to milk fever. It seems to be something about the way cows metabolize dietary rather than stored calcium.. they can’t transition fast enough (after they calve) to utilize the dietary calcium and so their body’s calcium stores plummet). Anyway… do you know anything about this? We have marginal pasture but we grow alfalfa hay and had planned to use it as our feed source to supplement poor pasture, but now I’m worried.

So, you say your pasture is ‘marginal’; how marginal? Do you mean that it would not by itself be adequate nutrition for a heifer, or bred heifer, or lactating cow, or whatever? How sure are you? It has been our experience that most folks grossly underestimate the nutritional value of their ‘unimproved’ pastures. We hardly ever visit a farm where the default groundcovers/forages won’t support a bovine without supplementation.
If you do decide you need to supplement — and it’s great that you can make your own alfalfa hay — you would in any case be well advised to drop the supplement in the last weeks before calving. Both old and modern wisdom recommends a more fibrous, lower calorie diet for late-gestation cows (‘putting her in a negative energy balance’ is how our veterinarian son expresses it). This is partly because fat cows have more trouble calving, but also because it is better for a cow to move somewhat gradually into milk production, not slam into it like a freight train. You don't want to feed them high and have them begin lactation at peak production. So we keep cows on brown or more ligneous forages for several weeks before and maybe a couple of weeks after calving — at least, that’s the plan, and we’re always better off when we don’t deviate from it.
In any case, we would encourage you to consider the possibility that you won’t need to supplement your pastured animals. It might seem like a great idea -- after all, the hay is free! -- but remember that when you offer non-pasture options, you short-circuit the foraging instinct that teaches a cow to self-medicate. We're not saying that you shouldn’t do supplement, but you should at least know there isn’t a necessity for it.
We hope this helps! Do keep in touch, we’d love to hear how it goes. Thanks for reaching out!