At birth, calves are essentially monogastric animals, according to Penn State University professor Jud Heinrichs. Their initial, liquid diets bypass the undeveloped reticulum and rumen, and flow directly into the omasum followed quickly by the abomasum.

Only when calves start consuming dry feed can rumen development begin. Starter grain intake promotes important bacterial growth and amino acid conversion that allow the rumen to grow and become functional.

Research has shown that once a significant amount of starter or grain is consumed by the calf each day (approximately 0.25 to 0.4 lb. per day), it takes about 3 weeks to then develop the rumen to the point that this digestive organ by itself has an established microbial population and enough absorptive capacity to allow the calf to continue normal growth once milk or milk replacer is stopped (weaning). If liquid feedings are removed before rumen development has occurred, the calf will not grow and may even lose body weight for 1 to 3 weeks until the time that the rumen is developed.

Thus, starter grain intake is paramount to a healthy weaning transition, and must start well before weaning occurs. Heinrich said any time a 2-week-old calf is not eating grain,

stop and determine why they are not eating it. If they are not eating a half pound a day by 4 weeks of age, again, look for the cause.

“Any time we evaluate the cost of feeding and maintaining a dairy replacement animal, the preweaned calf is always found to be the most expensive per day (primarily labor and feed), while the first group after weaning is the very least expensive replacement animal,” said Heinrich. “Thus, age at weaning and heifer economics go hand in hand. Obviously, weaning at a reasonable age is only part of the equation, as we want calves to continue to grow at all stages. Thus, rumen development is the key.”

Source: DAIReXNET. The full text of Heinrichs’ article can be found at:

http://www.extension.org/pages/71110/rumen-development-in-the-dairy-calf#.VFf7H6zwumQ.