Getting Inside the Rumen

I wrote before about what the rumen is and a bit about how it functions.  Recently I ran across mention of fistulated/cannulated cattle on another blog.  My freinds tend to refer to them as my washing machine cows.  I see these guys every day, they are my research steers.  But I was reminded that not everyone knows about them or understands why and how they come to be.  Cannulas can be placed in other locations, but 90% of the time with cattle we are talking about rumen cannulas, so that's what I'll discuss here.

So, let's begin with just a bit of terminology.  A fistula is a hole.  Specifically it is a connection between two organ or other structures that does not normally exists.  These can occur naturally or can be created by trauma or surgery.  The cannula is the rubber or plastic piece that is inserted to keep the fistula open for access.  The tubes used for tracheotomies?  Those are cannulas.  Just much smaller than the ones we use with cattle.




The next question is always why.  Why do we need cannulated animals?  The simple answer is research.  The long answer is complicated.  Cannulated animals most commonly give us access to the rumen of the cow or steer.    This allows us to take samples from or place things into the rumen.  There are a wide variety of reasons for doing this.  Using some of the research here at the University of Kentucky for a few examples:

1) In my research, we place fescue seed directly into the rumen to induce fescue toxicosis.  Relying on the animals to eat the seed is problematic as it doesn't taste very good and one of the complications of toxicosis is reduced intake.  By placing it into the rumen through the cannula we know exactly how much each animal is receiving each day. This makes the resarch more repeatable and reliable.

2) In situ research.  In situ is Latin for in place.  By placing feed in mesh bags on strings and 'hanging' them in the rumen, we can see how much of the feed is digested over a specific amount of time under controlled circumstances.  Changing the animal's diet, the room temperature, etc changes how the feed is digested.  Better digested feed = less needed to provide the same amount of nutrients.

3) In vitro fermentation.  Again, we scientist types like Latin.  In vitro refers to experiments that simulate animal conditions in the lab.  Most often, we do gas production measurements.  By incubating rumen fluid with various feeds or additives and examining gas production (carbon dioxide & methane) we can predict how these things will affect an animal.  As bloat is a huge issue in the cattle industry, finding natural gas suppression methods is a big deal.

This video from Kansas State gives a good view inside:

I hope this helps answer a few questions.  As always, let me know if you want more information, something doesn't make sense, etc.  It's easy to forget that what I do is unusual when I have done it almost everyday for years.

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• The Mysterious Rumen
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The Mysterious Rumen

Cattle have four stomachs.  Right?  This is what I was taught as a child and it seems to still be out there.  But, like many 'facts' we learn in grade school it's not quite correct.



Alright, so if cattle don't have four stomachs, what do they have?  They have a single stomach with four compartments.  These are the rumen, reticulum, omasum, and abomasum. The first three are often referred to as fore-stomachs (this might be the origin of the confusion).  These are non glandular, meaning they don't secrete acid and other substances like your stomach.   The abomasum is referred to as the true-stomach and is glandular.

Still with me?  Right, so, if there are no secretions, what do the fore-stomachs do?  They serve as the location of fermentation.  They are the home of all the lovely little microbes that digest plant matter. 

The rumen is the largest portion.It is fully lined with papillae that absorb nutrients produced from microbial digestion of feed.  Mostly volatile fatty acids (VFAs) are absorbed here.  The rumen is subdived into several sections called sacs, and I could spend this whole post on just the rumen and how it functions.  But lets save that for another day.

Rumen papillae (from Colorado State's fabulous webpage)

The reticulum is contiguous with the rumen.  Visually the way you tell the difference is that the papillae in the retuculum are in a cool honeycomb pattern.  I was so surprised the first time I saw a reticulum first hand and could see so easily the honeycomb I had always heard about.

Pretty awesome right?  (University of Washington)

Third on our list is the omasum.  It is really neat looking, round and about the size of a basketball.  No, really!  When you remove the digestive tract there is this hard, round structure.  Open up, it has leaves, like the pages of a book.  They are attached to the outer wall and meet in the center to form a sort of channel through the structure. 

Omasum half (creative commons images)

 Unfortunately, no one really knows what the omasum does.  It is thought to function as a sieve, making sure that food particles are small enough before passing into the glandular stomach.  It might also be involved in water absorption, recycling it to the rumen, where water is quite important for fermentation.

After all this, food enters the abomasum.  It works just like yours and my stomachs.  Acid (HCl primarily), mucus, and enzymes are secreted to digest food particles.  After that, it's onto the hindgut (intestines).

Abomasal tissue has folds, but no papillae. (Colarodo State)

I hope that clears things up about the number of stomachs a cow (or sheep or goat) has.  Any questions?  Want more information?  Suggested topics for the next post?  Thanks for reading!