Each year we put in Kale & Swede mixed crops to feed our cows over the winter months when they are not milking but the grass isn't growing (grass grows at 9-10'C but optimal growth is at least 12'C ) We also lock up grass paddocks to feed off over winter , we feed Hay to keep our ladies warm and feed Silage ( grass cut in Summer months when growth is booming, sealed and covered to allow it to slightly ferment. Which the cows absolutely love.
Once the winter crop paddocks have been fed off and the ground temperature is warming up, we replant a mix of grasses, clovers and colt foot. Having a variety is important for the nutrition of our cows and keeping them in good health, also future proofing the farms cover so if any particular strain of grass was to be susceptible to a blight or drought. You wouldn't lose the whole cover to the entire farm.
Different species of grasses have different root depths and the deeper the root is allowed to grow by not over grazing the top too low (over grazing puts the plant in survival mode and you won't get the full nutritional properties from the plants because they cant grow to their full potential and recover in time to be grazed again ) means the plant can draw up the nutrients just out of reach of other species that have a shorter root structure. Which in turn is passed onto our cows to keep our ladies in optimal condition and health.
Each year we rotate our winter crop paddocks and slowly work our way around the farm giving paddocks a new lease of life.
So nice wish that I am a part of your job