Is this a show heifer? You can introduce a grower but my experience is that we always have supplemented heifer grower mix with 50% to 70% precon pellets and fiber such as cottonseed hull or even fill . You can get bale of fill at Tractor Supply that works great and is cheaper than natural fill but it's mainly the fiber you are adding.
Heifers need 2 to 3 % of feed to grow with a 12 to 14% protein. Heifers need fat in the diet, but you have to be diligent and not get them too fat. If you are buying Precon, you can contact the Purina Rep in your area as well and they can put together a good formula for you.
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