dcara,
Before you can truly decide what you need, you need to know what you already have.
Much like people, cattle do not really need much in the line of extras if they are getting a truly balanced diet.
So, the first step you need to take is to call up your local feed guy. The one that has a reputation for service and honesty. Almost every area has at least one of these. Ask him to have his nutrition rep come out to your place and take some samples of the various feeds you are providing for your animals.
Around here, they will come and take the samples for free if you buy from them. We have this done every year. It does pay off.
This field man will sample the grass, possibly the soil and certainly any hay and supplements you are feeding. He will analyse these samples and provide advice as to what the cattle are getting or not getting.
He will then ask you what YOU want. Are you feeding for growth, fertility, young cattle, gestating cattle, and so on. You may have several groups of cattle, and be feeding for all of the above, or you may simply be backgrounding animals for sale at a later date.
Once the field rep knows what you want for your herd, he will take the information he has from the samples and put it together with the information you have provided.
With all of this information he will provide a feed plan that in almost all cases will exceed that of the people who do not take advantage of this service.
Work with someone who you feel comfortable and within a few years you will actually be very happy with the results.
Keep this relationship going over the long term - it does pay off.
Remember, the feed guys really do know their stuff - after all they have to keep their customers happy - otherwise they go belly up.
Regards
Bez