Bulls are herbivores, meaning their diet consists solely of plant matter. A bull is an intact male bovine, and like all cattle, its anatomy is specifically adapted to process rough, fibrous vegetation efficiently. The bovine species belongs to the order Artiodactyla, or even-toed ungulates, which are predominantly grazers and browsers. Their digestive system cannot properly utilize or thrive on meat-based diets, which ties their ability to convert forage into energy and muscle to their unique biological structure.
The Ruminant Digestive System
Bulls possess a specialized four-compartment stomach system, classifying them as ruminants, which allows them to extract nutrients from plant material indigestible to most mammals. The first and largest compartment is the rumen, which acts as a massive fermentation vat.
The rumen hosts billions of microorganisms, including bacteria, protozoa, and fungi, which are the true digestive agents. These microbes use enzymes called cellulases to break down cellulose, the tough carbohydrate in plant cell walls. This microbial fermentation produces volatile fatty acids (VFAs), which the bull absorbs as its primary energy source. The bull then regurgitates partially digested food, called cud, to re-chew and further break down the fiber, a process known as rumination.
The other three compartments each play a distinct role. The reticulum traps heavy or foreign objects and moves smaller particles into the next chamber. The omasum absorbs excess water and reduces the particle size of the feed. The abomasum is the “true stomach,” where hydrochloric acid and digestive enzymes break down proteins and microbes before they pass into the small intestine for final absorption.
The Foundation of a Bull’s Diet
The bulk of a bull’s daily intake is roughage, which is plant material high in structural fiber. Forage, such as fresh grass in a pasture, is the most natural and readily consumed food source. Bulls spend significant time grazing, harvesting plant material with their tongues and dental pads.
When fresh pasture is unavailable, the diet relies heavily on conserved forages like hay and silage. Hay, which is dried grass or legumes like alfalfa, provides essential fiber that stimulates rumination and saliva production. Silage is fermented, high-moisture forage, often corn or grass, which offers concentrated energy and protein.
The fiber in these feedstuffs promotes the constant chewing and saliva flow necessary for optimal rumen function. A mature bull may consume roughage equivalent to 1.5% to 2.5% of its body weight in dry matter daily. The quality of this foundation feed determines the level of supplementation required to meet the bull’s nutritional demands.
Nutritional Needs for Health and Performance
Roughage forms the basis of the diet, but supplemental feeding is often required to meet the high energy and protein demands of a bull, especially during growth or breeding seasons.
Protein and Energy
Young, growing bulls require a diet containing a higher percentage of crude protein, sometimes up to 13.5% to 14%, to support muscle and reproductive development. This protein is supplied through supplements like soybean meal, cottonseed meal, or dried distillers grains. Concentrated feeds, such as cereal grains like corn, oats, or barley, supply energy beyond what forage provides. These energy-dense grains are incorporated into the ration to support daily weight gain goals, often targeted around 1.5 to 2.0 pounds per day for young bulls. Grain content must be carefully managed, as excessive amounts can cause digestive upset or fat deposition, negatively affecting fertility.
Micronutrients and Management
Micronutrients are a specialized component of the managed diet. Mineral and vitamin mixes containing elements like calcium, phosphorus, and zinc are necessary for bone strength and reproductive function. Zinc supplementation, sometimes targeted at 60 parts per million (ppm), has been shown to benefit semen quality and fertility. Dietary adjustments are made throughout the year, as mature bulls often lose weight during the breeding season and require increased nutrition afterward to regain condition.