@simplysouthern22 ; welcome to the forum. You are commenting on a thread that is over 4 yrs old.
Mastitis has little to do with the CP levels. Most of the time CP levels that are too high will cause cows to get very loose manure... squirts as it is called on many dairies here... winter scours.... but it is really just that they are getting more protein than they can utilize. You cannot feed different rations to get different amounts of milk morning and evening. Basically the amount of feed will control the amount of milk, but again, not going to affect milk output as much from one milking to another on a regular basis.
I feed my dairy cows a 16% sweet feed when I milk. Actually it is a mix of 14% sweet with some 18% protein dairy pellets added in for the jerseys as they seem to milk more "off their back" than the jer/hol crosses. The guernseys and guernsey crosses seem to milk the fat off even more than the jerseys. The sad thing is the guernsey breed has been tampered with more than any other breed and it has caused problems; as they were not meant to be "milk wagons" and have been bred to be too "dairy" and not the more sturdy and even coarser looking cow. I have used a few outcrosses to less "dairy" (meaning fineboned and dainty) lines to try to breed back in some more "strength" into them.
I would look more to environmental causes for the mastitis. Are you doing a share situation with the calf? I have done that often, only milking once a day and the calves on the cow for 12+ hours; separating them away from the cow so I can milk 12 hours late. Calves have often been the way to stop mastitis in cows as they will butt and milk out the udder more often during their time with the cow.
Are you getting enough milk from the cow? Does she seem to have milk in her udder when you separate off the calf in the evening? If so, then the calf is not milking her out enough. She could very well need another calf. How much milk are you getting? How much milk do you need? If she has milk when you lock the calf away in the evening, then the answer is to feed less overall grain.... so her production drops off. My suggestion is to not feed as much grain in the evening... and I would just stick with one grain mix. 16% all the time. You are upsetting the bacteria in the gut tract by constantly changing the protein. The amount of grain will affect the beneficial bacteria in the gut tract and the rumen bacteria.... but constantly changing the protein will also cause havoc. Whenever a dairy changes their feed program due to changing which silage they are feeding, they do not want me to come milk test for about 5-7 days so the cows get adjusted to it and then they will get back to milking normal. It can really throw them off. You are in essence doing that to them every day.
I would see if your state agriculture lab does milk sample analysis. They can check for BF, protein, SCC ... and can isolate the type of mastitis. I also know that the lab in Lancaster PA does this. It is not cheap... but if you are having a problem, you need to know what is causing the problem, if it is treatable and what to treat with. Sometimes there are cows that are chronic high SCC cows... and getting rid of it is tough. Staph bacteria is a common chronic problem. Strep is also a common one. Some will be treatable with antibiotics... but chronic cows often will have a resistant strain and will not respond. You won't know if you don't know what you are dealing with.
I will be glad to help if I can. Another question.... are you near a dairy that you are friends with? Ask if they are "on test".... many dairies are on some type of DHIA test...or with Dairy One.... which is a milk test that samples from every cow get sent into a lab to check the individual cows. If you are friends with a dairy... see if they would send in a sample of your cow with their monthly test. They would have to create a "fake cow" in their herd.... and you would have to give them a milk weight for the cow, but they can take a sample of your cow and send it in along with their herd info. Within a few days after the samples are run, they can tell you what the sample showed... the BF % and the protein and SCC... if it is high... then you have to go from there. I have 2 former dairy farmers with just a couple of cows they still have, that partner with another farm for the samples... it costs about $5 a sample if sent in with a farm already on test. It would cost you 5-10x that much to be on test yourself.... there are rules with these companies for minimums etc....
Again, some of the state labs do sampling. I can get you in touch with the Lab in Lancaster Pa that processes our DHIA samples and they have many farms that do what is called owner sampling. I don't know the particulars on costs. Again, there are minimum charges, but it is a way to get results.
Hope this is of some help.