I have something to share about DMI as soon as I get permission.
Denny, I think what you are planning to do is sound. I wish knew more about corn silage and I would be even more sure.
As with all feeds, Dry Matter Intake (DMI) is key, along with water.
With 64% TDN in your silage....which was 40# as fed, containing 65% moisture.......that gives you 14# DM....x 64% TDN....almost 9# energy. Plus what you get in the alfalfa.
I found this table which shows the nutrition requirements of a beef cow at different stages of gestation/lactation.
Scroll down to page 12. I tried to bring the table over here, but it didn't transfer well, so best to just check it out using the link:https://www.bookstore.ksre.ksu.edu/pubs/C735.pdf
For example, it shows 1300# cow, mid third pregnancy needs 22# DM; 10.8 TDN; 1.5 Crude Protein. I suppose this is at 20 degrees.
Colder than that the requirements go up substantially. Last trimester requirements go up too. It's a good chart, same as what I have. Came from the NRC published in 1984. To my knowledge, there hasn't been new research by the NRC since.
Figuring your silage alone looks like almost 9# TDN, so you have almost met that requirement. You have 14# DM, so you need an additional 8# of that to make 22#. I know our cows needed more than 22# when it was cold and windy. So keep that in mind.
(10# alfalfa hay @ 14% moisture yields 8.6# DM so adding that to your silage, you have met your DM requirements at 20 degrees.) 10# alfalfa @ 17% Protein results in 8.6 DM x 17%=1.46# Crude Protein. 14# DM silage x 8.5% Protein = 1.19# protein. Now you have 1.19 + 1.46#--2.65# total of Crude protein from the silage and alfafa. The alfalfa PLUS the grass hay would put you over the requirements, which is a good spot to be in going into the winter. It is so much easier to keep them in good body condition and MAINTAIN during the winter as to try to catch up when the winter is cold; sometimes you can't feed enough! Your grass hay will be good to feed as it isn't as digestible as the alfalfa/silage and looks to me you would have a nice balanced feed for your cowsand would give them more DM. Feeding 40# silage; 10# alfalfa (you might be able to cut back to 5#) since you would be adding some grass hay. The grass hay is important, even though it isn't quality feed like the alfalfa. Cows will utilize it and do well having it. Dry matter, dry matter, dry matter.
There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.