Final answer:
Calves, as ruminants, undergo a dietary transition from milk to forage as their rumen develops, usually by the age of 6 to 8 weeks. Their specialized four-compartment stomach—rumen, reticulum, omasum, and abomasum—enables the digestion of fibrous plant material. Once fully developed, the rumen utilizes microbes to ferment cellulose, facilitating the weaning process.
Step-by-step explanation:
The transition of calves from milk to forage is involved with the development of their rumen. As herbivores, calves belong to a group of animals known as ruminants, which also includes cows, sheep, and goats.
These animals are adapted to a diet rich in roughage or fiber and have specialized digestive systems with four compartments to process their food: the rumen, reticulum, omasum, and abomasum. Initially, calves consume milk which bypasses the rumen and goes directly to the abomasum.
However, as they grow, their rumen develops and becomes capable of digesting solid forage.
Cattle that are grazed on open lands are generally allowed to reach market size before being placed in a feedlot. In contrast, some cattle are kept on grass diets their entire lives, which is considered to produce healthier and tastier beef that commands a higher market price. Once the rumen is fully developed, usually by 6 to 8 weeks of age, calves can be weaned off milk and transitioned to forage.
This allows them to utilize the microbes in the rumen that break down cellulose and ferment the ingested plant material. When ruminants consume food, it is chewed and passes through the esophagus into the rumen for fermentation. Cud is then regurgitated from the rumen, chewed again, and swallowed to the omasum and eventually the abomasum for further digestion.