Below is a tidbit from "Feed and Care of the Dairy Cow" ©1898
In a herd of fifty cows, the average amount eaten, per cow. will correspond closely with the amount given in the one hundred rations, but individual cows will vary widely from the average. some eating not more than half the amount called for in the ration and others eating and giving returns for twice the amount. We find many Kansas dairymen feeding all cows in a herd alike, the fresh cows, the cows that have been milking six months and those nearly dry getting the same amount of grain. This is a mistake. In most herds cows will be found that, after milking three months, begin to put on fat and slacken in milk yield. As soon as the first signs of this appear, cut down the grain ration. Other cows will be found to keep thin, turning all their feed into milk. Increase the feed of such cows just as long as they will give returns for it. In the same herd we have with profit varied the grain ration for different cows from two to twenty-four pounds. If the dairyman has the conveniences it will pay to vary for each cow the proportion in which the grains are given, which is easily done if the grain mixture is fed from awbox mounted on low wheels. Fill the box with the mixture of grain selected for the ration, select the two grains in your mixture that are "respectively richest and poorest in protein and put them in small boxes on your feed-box. Taking ration No. 38. the feed richest in protein is cottonseed meal, that poorest in protein is Kaflir cornmeal. You come to a cow that is milking well but is beginning to put on flesh; give her only a part of a feed of the general grain mixture and add some cottonseed meal; this will tend to force her to a higher milk yield. The next cow may be a heavy milker that is getting so thin that she is losing vitality; give her only a part of a ration of the general mixture and add a liberal allowance of Kafiir corn meal. This will help her put on flesh enough to keep up strength. The nearer each cow’s wants are met, the greater will be the yield and the more the profits. Feed according to the _vield of milk and the condition of the cow.
This publication also notes various types of feed. Here's a partial list:
Red Clover Hay
The list goes on but have fun with it, try and decide which diet your characters are feeding their cows and if it works well for them or not.