In contrast, the abomasum comprises only 20 percent.
The omasum still makes up about the same proportion at 10 percent. By 12 weeks of age, the reticulum and rumen will make up more than two-thirds of the total stomach capacity. The stomach compartments grow in proportion to the calf's body size. By 4 weeks of age, the reticulum and rumen comprise roughly 58 percent of the stomach, the omasum remains the same at 12 percent, and the abomasum falls to about 30 percent.
At birth, the reticulum and rumen make up 30 percent of the stomach capacity, and the omasum makes up approximately 10 percent. In contrast, it makes up only 8 percent of the stomach capacity in a mature cow. The abomasum constitutes 60 percent of the young calf's stomach capacity. As the calf grows and begins to consume a variety of feeds, its stomach compartments grow and change accordingly (Figure 1 and Table 1). The newborn's functional stomach, the abomasum, is similar to a human's stomach. However, the calf's reticulum, rumen, and omasum are inactive and undeveloped. AnatomyĪt birth, the calf's stomach contains the same four compartments found in adult ruminants. The fascinating differences between calves and mature ruminants create unique nutritional needs for preweaned calves. The stomach compartments grow and change as the calf develops into a ruminant animal. As the calf begins to eat dry feeds, particularly grains containing readily fermentable carbohydrates, the rumen takes on a more important role. The abomasum is the only stomach compartment actively involved in digestion, and milk or milk replacer provides nutrients. From birth to about 2 weeks of age, the calf is a monogastric, or simple-stomached, animal. At birth, the dairy calf's digestive system is underdeveloped.
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