Studies in the United States indicate that 70% of calves are weaned 7 weeks of age or later.  This is in light of calves with adequate rumen development can be physiologically ready for weaning as early as three weeks of age (Pennsylvania State University).  Getting calves to weaning earlier not only saves money but also saves time spent in the calf shed. 

Calves are born pre-ruminant. All four stomachs are present, but the rumen is underdeveloped in neo-natal calves.  Milk by-passes the first three stomachs and enters the abomasum directly where it is digested.  Solid food however passes directly into the rumen (the first stomach) to begin a journey through the four stomachs. 

Early rumen development is essential for successful rumen development.  When a calf begins to eat dry feed, such as a textured starter feed, the rumen begins to supply nutrients produced by fermentation and the population of rumen bacteria begins to grow.  Fermentation of the starch component in grain produces volatile fatty acids (VFA), particularly butyrate which stimulates the growth of rumen papillae and metabolic activity in the rumen.

Rumen development can be assisted by providing easy access to water in conjunction with a textured starter feed in the first few days after birth.  This feeding strategy promotes the early development of the rumen so that the calf is physically prepared and ready for a change of diet to solid feeds by three to four weeks of age. 

After three weeks of consuming a textured calf feed (grain-based), a calf’s rumen will have enough bacteria fermenting enough feed to supply a substantial amount of energy.  The bacteria in the rumen also provide an additional source of nutrition called microbial protein which is digested and absorbed in the small intestine after they are washed out of the rumen.  The microbial protein is highly digestible and contains a very favourable profile of amino acids to support the needs of the growing calf.

Rumen development is triggered by the digestion of the starch which is found in the grain present in textured starter feeds.  From a physiological perspective, it takes approximately 21 days for the rumen papillae to develop from the initial consumption of grain. 

When assessing an appropriate starter feed, look for a textured feed that contains steam-flaked grains. Steam-flaked grains are highly digestible making the starch more available to the calf.  The process of steam flaking produces grains that are more gelatinised and more digestible in the undeveloped rumen of a calf. 

The main point to take from this is that although calves have the physiological potential to be weaned between three to four weeks of age, Pennsylvania State University studies have shown calves weaned at this early stage require extra attention and that waiting to wean at four weeks is prudent.

It is essential to remember that early weaning can only take place in conjunction with early rumen development.  If the rumen is not developed to handle dry feeds the calf will suffer a growth check for up to three weeks post-weaning. 

To capitalise on the benefits early weaning presents, attention must be given to health and growth up to six months of age while the rumen continues to develop.  Complete rumen development takes place between 4-6 months of age.