What are animals fed and why?

Some animals, like cattle and sheep, are what animal scientists call “ruminants,” which means that they digest their food by fermenting it in a four-chambered stomach. Inside the stomach, there are bacteria that work to break down the tough stalks of the plants the ruminant animal has eaten. This allows them to eat and digest food that other animals, including humans, cannot. The bacteria can also help produce nutrients for cattle just by living in the animal’s stomach.

Ruminant animals should be fed a diet that consists mainly of forage (like grass) or roughage (like hay). When these feeds are broken down in the stomach, they can provide energy and protein. This is the diet that is most natural for the animal.

At certain times in their lives, ruminant animals may need more energy to help them produce milk or gain weight. Energy in animal feed usually comes from grains, which can be fed alone or as part of a total mixed ration (TMR). A TMR is any animal ration that has multiple kinds of feed mixed together, which prevents the animal from only eating what it likes.

When beef cattle and lambs are being prepared for market, they are sometimes fed TMRs that contain a mixture of roughage and grain. The grain in the TMR provides energy in a more concentrated form, which allows the animal to grow faster and be more efficient with its food.

Corn stalks stored as round bales. Photo from Scott Radcliffe, Purdue UniversityDairy cattle are also fed TMRs. These consist mostly of hay or corn silage, which is produced by grinding the whole plant at harvest and then fermenting the mixture in a silo. The grains in the TMR help the dairy cow to produce milk that is high in butterfat, which makes the milk more valuable.

Farmers need to be careful, though, because feeding too much grain and not enough forage and roughage can make a ruminant animal sick.

Non-ruminants, which are animals like chickens and pigs, digest their food more like people do. In fact, they can live without any hay or grass. Instead, they are fed mixed rations of energy and protein, which usually come from corn (energy) and soybean meal (protein).

Alternative feeds

Feeding animals is the most expensive part of animal agriculture. To keep costs low, some farmers feed by-products from other industries to reduce the amount of hay and grain they need to buy. These products, like distiller’s grains and soybean hulls, contain valuable nutrients. Feeding them to animals prevents waste and helps the farmer to save money.

Feed additives

In addition to protein and energy, animals also need vitamins and minerals. Farmers can buy vitamin and mineral mixes that can be added to their animals’ daily rations, or they can feed it to the animals in a solid block that the animals can lick while they are out grazing.

Calcium and phosphorous are two very important minerals in an animal’s diet. Under normal circumstances, the ratio of calcium to phosphorous should be about 2:1 in order to keep the animal’s body functioning properly. One way to keep this balance is to feed dicalcium phosphate, a compound which has the right balance of calcium and phosphorous for an animal diet.

Sometimes, the farmer will want to give his animals medication to treat or prevent disease. This medication can also be mixed into the animals’ rations. The farmer has to be careful when he or she feeds this, because animals going to market must be taken off medicated feed weeks in advance in order to give the medicine time to wash out of their bodies. This period of time when the animals cannot have medication in their feed is called the withdrawal period.


Too much fat can cause health problems, but fat is not all bad. In fact, humans and animals need fat in their diets in order to stay healthy.

Fat is involved in several important body processes, including liver function and the creation of chemicals, called hormones, that send messages in the body. Fat also provides the most energy out of any of the nutrients.

Energy, in nutrition, is measured in units called kilocalories. In human nutrition, a kilocalorie is the same as a Calorie, spelled with a capital C. These are the units that show up on the “Nutrition Facts” on the side of your cereal box. Every gram of fat provides nine kilocalories. Every gram of carbohydrate or protein provides four kilocalories.

Fat in an animal’s diet can come from some of the food they already eat. It can also come from supplements, like fish oil, that the farmer can feed if that animal needs the extra energy.

Baby animals

Most baby animals are fed on milk from their mothers for the first weeks or months of their lives. When the animals are old enough and nearly ready to be taken off their mothers, the farmer may choose to start creep feeding. Creep feeding involves putting hay or grain behind a special fence that allows the baby animal access to the feed without letting their mothers get in and eat more than they are supposed to. As they grow, the baby animals may have to crouch down, or “creep” to get inside the creep feeder, which is where the process gets its name.

Unlike other farm animals, baby chicks and other hatching species are not fed from their mother. When they first hatch, the yolk of their egg is absorbed into their intestines through a special opening, like a human navel. The yolk has enough nutrients for the bird to not have to eat for two days. When the chicks arrive at the farm, they are fed the same feed as the adult birds.

And what about horses?

Horses are unusual. They aren’t ruminants, but they’re not non-ruminants either. Instead, they are what are called hindgut fermenters.

Horses’ stomachs are a lot like non-ruminant stomachs. They secrete digestive liquids that help the horse to break down the food they eat. These kinds of stomachs are not good at breaking down fiber, which is found in the stems of grass and hay.

But horses eat grass and hay. So why can they do that?

Horses can digest hay because they have an enlarged cecum, or appendix, that can hold about eight gallons of feed. The cecum acts like a ruminant animal’s stomach. It has bacteria and other microorganisms that help the horse to break down the fiber in its diet. In this way, horses can function like a ruminant animal.

Because of this, horses should be fed like ruminants. The majority of their diet comes from forage or roughage and any extra energy comes from limited amounts of grain.


Though it is often forgotten, water is perhaps the most important nutrient of all because it is needed for almost all processes that happen in the body. Humans and animals can survive weeks without food but only a few days without water. Therefore, it is important for the farmer to provide plenty of fresh, clean water at all times.

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