Ruminants explained

Ruminants are classified into three main feeding categories - browsers, grazers and mixed or intermediate feeders.

Ruminant livestock include cattle, sheep and goats.

According to Wildlife Vets Namibia, plant material is not easy to digest as it contains a lot of cellulose.

“Luckily for the ruminants, they have a whole army of micro-organisms in their gut working hard to convert plant material into nutrients that the animal can use.”

Wildlife Vets explained that rumination is a process that sees already-swallowed food brought up, chewed again and swallowed once more.

“It involves regurgitation, bringing swallowed food back into the mouth, remastication, insalivation and deglutition.”

Rumination therefore allows animals to chew food more completely and this, in turn, improves digestion, it said.

“The smaller the pieces of food, the better the micro-organisms in the rumen can do their job.”



Anatomical differences

According to Wildlife Vets, an advantage of this adaptation is that the ruminant can spend more time resting, while looking out for predators.

Animals can stand while ruminating, but usually lie down.

“What is interesting is that within ruminants, there are a lot of anatomical and functional differences per species. These modifications have evolved in such a way that the most nutrients can be extracted from the food they eat.”

These differences go further than just the diet of an animal.

Wildlife Vets noted that the mouth structure of an animal influences its bite size.

For example, many grazers have wide muzzles to maximise bite size. At the same time, this wide muzzle limits them from selecting smaller, more nutritious grasses.

Browsers, on the other hand, usually have a narrower muzzle and a large mouth opening to strip off leaves. Giraffes have long tongues, and black rhinos have prehensile lips.

On average, the salivary glands are larger in browsers than in grazers, it said. One explanation is that the larger salivary glands in browsers produce tannin-binding salivary proteins that partly help to prevent tannins from reducing the protein digestibility.

Browsers also have more liver tissue, a possible adaptation to the higher amount of chemicals in browse compared to grass.

“When we look at their gut, we see that all ruminants have one or more portions of their gut ‘dedicated’ to house the micro-organisms.”



Digestion process

According to Wildlife Vets, in the rumen, microorganisms digest the plant material - they break down plant components such as cellulose, which is then converted to glucose. The next stomach, the reticulum, has a pouch-like structure, and determines whether the food is digested enough.

“When the food is not digested enough, the animal must ruminate. Grazers tend to have a larger, more muscular and divided rumen/reticulum to digest the cellulose more effectively.”

The next stomach, the omasum, has many large folds to create a big surface where water and other important nutrients are absorbed, it said.

Meanwhile, the last stomach compartment, the abomasum, is similar to that of humans. Here, acid and digestive enzymes are produced which kill bacteria and break down more nutrients.

“Browsers usually have a proportionally larger abomasum and a larger hindgut than grazers, to favour digestion of some of the plant cell contents.”