The Truth about CMR, Part 2 - Rumen Development

21 February 2018

 Jim Uprichard

In the second installment of his article about best practise in calf nutrition, Jim Uprichard turns his attention towards the development of the rumen in the young animal...

In the early stages of a calf’s development, all of the energy is supplied from intestinal digestion.

This is because the reticulum and rumen are sterile at birth, making the neonate calf essentially a simple stomached animal. It is at least 2 weeks before the rumen microflora start to develop, and a further 4 weeks before they are in sufficient numbers to significantly contribute to the calf’s energy demands (Meale et al., 2017).

In the Teagasc publication, Development of the Calf’s Digestive system, it is stated that the immature calf’s digestive systems function similarly to those of a young monogastric animal, and the calf depends on milk or milk replacer as an easily digestible source of carbohydrates and protein.

While the Rumen is functioning by 6 weeks of age, it is not until the calf is 12 weeks old that the rumen is fully developed, and its ability to eat and digest dry food will then be more or less similar to that of an adult animal.

The diagram below illustrates the typical ages associated with stages of rumen development:

Age of Calf Rumen Development
Neonate calf  Intestinal digestion
2 weeks Rumen microflora start to develop
6 weeks Rumen microflora can significantly contribute to calf energy demands
12 weeks Rumen fully developed

Based on Table 1 (below), it is not until the calf is 63 days old that the rumen becomes a significant source of energy for the rapidly growing calf. Therefore, it is important for performance that a calf is not weaned too early. While a high quality concentrate should be introduced from the first week of life to drive optimal rumen development, milk is the main driver of growth during this development phase.


Table 1: Energy contribution from the abomasum/duodenum and rumen at various ages and body weights of calves (Doreen, 2012)

 Age in days  14  30  46  63  91  183
 Body weight  46  57  68  80  105  200
 % energy from abomasum / duodenum  100  80  60  40  30  20
 % energy from rumen  0  20  40  60  70  80


Calves weaned off milk before sufficient rumen development has occurred will have poor growth rates and may even lose weight for a couple of weeks after weaning, until the rumen has developed enough to provide sufficient energy. Solid feed (concentrate and straw) contributes to rumen development as it flows into the rumen where digestion begins.