‘What fuel is for a car, feed is for a cow – without it they are both useless.’
The biggest cost on any dairy enterprise is the feed bill. The most important management tool of the dairy farmer is to feed his animals correctly. The following is a very basic outline of the nutritional requirements of dairy animals.
CALF (See Calf Scours in the Dairy Herd)
A poorly grown calf will never be a top-producing cow, no matter how good the breeding. It is essential that the calf receives colostrum within 6 hours (preferably 2 hours) of birth at a rate of 10-15% of birth weight. She should get colostrum for the first 5 days of life; 2-4 litres/day depending on breed and birth weight..
At one week of age, she should be introduced to calf starter meal. 1 kg of calf starter meal is nutritionally equivalent to 2-2 ½ litres of milk at a fraction of the cost, so the sooner the calf starts eating meal the better. At 2 weeks, good quality roughage is introduced. The calf can be weaned once she is eating the roughage and 1.5kgs of calf starter/day. 
From weaning until 6-8 months of age, the calf should be fed on calf grower meal offered ab lib. She should have good quality roughage available at all times. At about 8 months, the calf becomes a true ruminant and is able to make better use of roughage.
HEIFER (See Dairy Heifer Growth Curves)
The heifer must be adequately fed to reach 85% of mature mass at 14 – 18 months of age, depending on breed when she should reach breeding mass and height and be ready for first service. For this stage she should have constant access to good grazing or roughage and bfed heifer meal at a rate of 2 – 6 kgs/day, depending on age size and condition of grazing. See heifer growth chart to ascertain targets.
The cow requires energy and protein for 
•    Maintenance (breathing, walking, rumination etc)
•    Growth (Ist lactation cows are still growing)
•    To produce milk
•    To produce calves
If the cow’s nutritional needs are not met, these functions cannot be carried out. As food is with-held the animal will
•    Stop cycling or not reconceive
•    Drop milk production
•    Growth is stunted
•    In extreme cases – die.
A very basic rule of thumb is to feed 2 kg of a lactating cow ration for maintenance plus an additional 0.5kg for every kg of milk produced per day. First calvers and cows in early lactation will require more. In addition, the cow requires good quality roughage, whether it be silage, hay, grazing, legumes. A cow cannot eat enough poor quality roughage to meet her needs, as it takes too long to digest. The better the quality of the roughage, the more she can eat, the more milk she will produce.
The Essential Nutrients
•    Water - A lactating cow requires 50-100 litres of water/day. Clean water should be available at all times.
•    Energy needed by the animal to do work, live and produce milk -  is found in concentrate feed, maize and other grain crops, molasses, good quality fibre such as good silage, rye grass, early grazing on planted pastures.
•    Protein forms building blocks for growth and living, also forms the main constituent of milk and meat. Therefore cows with higher production require more protein. Protein is found in concentrate feeds, young grasses, oilseeds and legumes.
•    Minerals and Vitamins  are supplied in the concentrate feed. It is essential that the lactating cow is fed the correct dairy concentrate feed, whether purchased or home mixed.
•    Fibre -  silage, good quality hay, grazing (early season) rye grass, legumes, crop residues etc.
DRY COW (See Management of the Dry Cow) 
The dry cow has different nutritional requirements to the cow in milk. The dairy farmer should aim to dry the cow off at a body condition score of 3.5 and maintain this body condition through-out the dry period. A specialised dry cow meal should be fed at a rate of 2-4kgs/day dependant on body condition and value of roughage. The cow should have access to good grazing or roughage.
Crop Residues can be a useful source of roughage, depending on the residue.
Stems/leaves cowpeas/groundnutBean and soya bean hay with leaves
Sweet potato vinesGreen maize stover
Green maize leavesSugarcane tops
Banana leaves - green 
Old brown maize stoverOld wheat straw and veld grass, even with molasses and urea.
Wheat straw 
Veld grass – still green