Why do cattle chew their cud? What is cud? Are
they born knowing how to do it? What triggers this response?
For us humans with our simple stomachs, it can
be a little hard to understand what goes on in the digestive system of a
ruminant animal. You may have thought about these questions – and others –
before, but it may have been hard to find clear answers. Let us spend some time
talking about cattle and their cud!
First of all, we know that cattle are ruminant
animals. This is commonly described as having four stomachs, but that is not
entirely accurate. It is more like they have a four-compartment stomach. Each
compartment has a different job, looks different, and is a slightly different
size. This impacts what kinds of foods they can eat, and the amount of
nutrients they can get from that food.
The four compartments of a ruminant stomach are
the reticulum, rumen, omasum, and abomasum. Food will first be chewed, then
sent down the oesophagus (like in monogastric animals like us), and then it
will land in the rumen.
The rumen is the largest part of the digestive
system and can hold up to 40 gallons worth of material. This compartment’s
basic purpose is to ferment the nutrients out of the food. Cattle are
herbivores, which means they only eat plants. As a general rule, the nutrients
in plants are harder to digest than the nutrients in animal proteins, partially
because they are locked in cellulosic cell walls. This makes organs like the
rumen so important and powerful for herbivorous animals; it can help “cook” out
those nutrients so the animals gain the energy they need. This also helps
explain why we humans eat salads and lose weight, while cattle can eat hay and
other forages and gain weight.
After the cattle’s food sits in the rumen a
little while, it travels to the reticulum. The reticulum’s structure on the
inside looks like a honeycomb. When food first comes into the reticulum, it is
generally not chewed very well. This is their cud. The reticulum will ball up
the portion of food sent to it by the rumen and trigger the regurgitation of
the cud. The cattle will then chew the cud more completely, and will swallow
again when they are done. This helps the cattle better digest their food. The
scientific term for “chewing their cud” is rumination. Cattle will spend about a third of their day
ruminating. When they have finished with this step, the food will travel to the
next stomach compartment.
The next compartment is the omasum. The omasum
helps absorb liquids. It is relatively small and has lots of folds. Since
liquids do not need to be digested to the extent of cellulosic feedstuffs, like
cornstalks, they will generally pass through the rumen and reticulum quickly to
reach the omasum, where they will get absorbed. In fact, there is a small slot
that opens from the reticulum directly into the omasum (the oesophageal groove) when a calf’s head is at
the right angle that allows milk to pass directly to the omasum. Therefore, for
the first portion of a calf’s life, it does not chew its cud – it does not have
any!
The last compartment of the ruminant stomach is
the abomasum, also known as the true stomach. This compartment functions much
like our stomach, using acids to further digest feedstuffs before sending it on
to the intestines. It is important that food gets thoroughly “cooked” and
digested before it reaches the intestines, because the small intestine (the
first segment of intestines) does most of the nutrient absorption in the
digestive system. This makes foregut fermenters (like ruminants) more efficient at absorbing
plant materials than hindgut
fermenters (like humans) who primarily ferment cellulose in the
large intestine.
If you are still a little shaky about how food travels within the ruminant digestive system, I would suggest watching this video:
So now, you know a little bit about cud! Go
ahead and surprise your friends with your newfound knowledge – but maybe not
over dinner.
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