What are the characteristics of rumen development in calves?

When a calf is newborn, the rumen is very small and its function is underdeveloped, while the abomasum is large, accounting for 70% of the stomach volume. After 3 weeks of age, the rumen gradually develops, and by 6 months of age, the combined capacity of the first 3 stomachs accounts for 70% of the stomach capacity, while the abomasum accounts for only 30%. By 12 months of age, the stomach is already close to the level of an adult cow. After one week, because the calf begins to eat forage, microorganisms enter the rumen through the mouth and multiply, beginning to show digestive function. At 3 to 4 months of age, a ciliate flora appears. After the calf eats forage, rumination occurs and the parotid glands secrete saliva, so feeding calves forage earlier can accelerate rumen development and promote microbial reproduction, allowing them to pass through weaning smoothly.