In the first week, the abomasum of the calf represents ca 60% of the whole stomach complex, and the rumen 25%. Where the abomasum of the adult cow represents only 7% and the stomach complex 80%. This means that the rumen undergoes a dramatic development, in structure and in size: the final size will determine the capacity the cow has to digest solid feed, and the digestion efficiency.
The rumen of a newborn calf is sterile, however, already soon after birth the calf will come in contact with its environment, and bacteria will start to colonize the rumen. Also milk will enter the rumen, as not 100% of milk is directly flowing to the abomasum.
For the establishment of a healthy bacterial population in the rumen, the calf needs to take up solid feed in the form of concentrates and roughage. This stimulates the rumen development. Ensure that the calf gets unlimited access to water. The solid feed will absorb the water and allow, together with the anaerobic environment of the rumen, the bacteria population to grow. These bacteria metabolize nutrients, and produce volatile fatty acids, like acetate, propionate and butyrate. These acids lower the pH in the rumen, ideal conditions for bacteria to grow even better. Thus the volatile fatty acids stimulate rumen development on itself. This optimal development of the rumen improves the absorptive capacity of the rumen wall, leading to efficient feed utilization!
At the moment the calf is about to be weaned, the calf should have a minimal concentrate uptake of 2,0 kg. This will assure the rumen is sufficiently developed and the calf is able to absorb sufficient energy when milk is taken off the diet. Gradual weaning will help stimulating the concentrate uptake. As well as feeding whey-based milk replacer, since whey does not form a clot in the abomasum, and therefore stimulates solid feed intake.