Article supplied by Dr B.W. Schouten, BVSc
Veterinary Consultant to AgriVantage


The transition from milk to grass

In the early stages of a calf’s life, milk is digested in the fourth stomach (the abomasum). Only when the calf has a fully functional rumen and reticulum (the first two stomachs) can the transition from milk to grass be made.

The rumen

The rumen is very small at birth (about the size of a fist) and is sterile. As the calf grows older, the rumen stretches and becomes a giant fermentation vat, full of useful bacteria able to break down and digest plant material, converting these to energy and growth.

By weaning, the size of the rumen is only about the size of a pillow but as an adult it has the capacity of a 200L drum.

So, when does this occur and what diet is the best to hasten rumenal development?

Rumenal fermentation starts as soon as plant material is introduced into the diet and full function can be achieved as early as 5-6 weeks of age, with the right diet.

Grass is a good feed to do this but, in the spring, it is often very low in sugars (soluble carbohydrates) and dry matter (15% DM) and can be as much as 85% water.

To get maximum DM and energy into the calf, you’re best to feed meal (concentrates) and roughage. Highly soluble carbohydrates and proteins are the ideal diet for a young ruminant.

Meal and roughage feeding for calves

The best supplementation is with concentrates (95% DM) that hasten rumenal development and smooth the transition from milk to grass.

Fibre (hay and straw) will also contribute to the ‘stretching’ of the rumen, but both these products are relatively low in energy and therefore should ideally not exceed more than 10% of the diet.

The so-called scratch factor of roughages is a myth and should be ignored.

A good quality meal must:

  • Be highly palatable

    i.e. it must taste good. The inclusion of 6-8% molasses greatly helps to achieve this, as well as also supplying a valuable energy source.

  • Be highly digestible

  • Be high in energy

  • Contain 16-22% protein

    A high protein level (20%) is needed when calves are indoors. When given access to good quality pasture, the protein level can be lowered to 16% without compromising growth rates.

  • Be high in vitamins and minerals

  • Contain rumenal buffers to prevent acidosis

    Sodium Bentonite and Bicarbonate.

  • Always contain a Coccidiostat (Rumensin, Deccox or Bovatec)

  • Be free of mould or fungi and smell good

Several concentrate products are commercially available and are sold either as meals, textured feeds or pellets. The choice is yours, so long as the above criteria are met.

The relative importance of the various ingredients is shown in Fig 1 below.


The diagram emphasises the importance of cereal grains as the major source of energy to drive rumenal fermentation – as any good home brewer would know!

Please note:

  • The ratios (in commercial concentrates) are carefully formulated and balanced to prevent digestive upsets and to give maximum growth

  • Homebrew cereal grain mixes are should only be used if formulated by a qualified nutritionist - mistakes in mixing rates can be disastrous and expensive.

Practical aspects of meal feeding

  • Start meal feeding from week one.

  • Sodium Bentonite (Trufeed, OptiGrow) sprinkled over the starter ration will often encourage early meal/pellet uptake and deter birds.

  • The size of the trough space is critical for an even early uptake. Meal troughs must be clean, preferably off the ground and under cover. There should be room for all the calves to get access to the trough – as a rule of thumb allow 300mm of trough space /calf.

  • Meal should be available ad-lib, topped up daily and any wet or mouldy product removed.

  • Keep chooks and birds away as much as possible (they can become a major source for bacterial infections and will/can spread bacterial and viral agents from pen to pen). A good practical solution is to fill meal troughs in the evening.


As meal intakes increase, so does the need for access to good quality water.

Inadequate water supply will reduce meal intake and calf growth dramatically - by as much as 60%.

Clean ad-lib water must be available to calves in adequately sized troughs.

Water quality is critical. Ask yourself, would you drink it? If no, do something about it.

Weaning criteria

Calves can be weaned from milk once all the following criteria are met.

Each calf must:

  1. Be over 65kgLW (preferably 80kg+), or at least 25kg above birth weight.
  2. Be consuming more than 1kg of concentrates for more than 3 days.
  3. Have a good pear-shaped abdomen – an indication of a fully functional rumen.
  4. Have access to good quality pasture more than 200mm high (6 inches) >1800kgDM/ha
  5. Continue meal feeding for at least another month or until 100kg+ body weight

Remember, meal feeding is not a cost, it’s an investment and a sure way to ease the successful transition of your calves from milk to grass.

Need advice on calf rearing? Please get in touch.