The fiber of forages

Relative feeding value, neutral detergent fiber, lignin.  These are all terms that can be found on any hay or grass analysis.  But what do they mean and how are they determined? 

Let's start at the beginning.  Sending in your forage to be analyzed is very important when developing a feeding plan for any species.  The values you get back tell you how the forage is lacking so that you can fill in the gaps without overfeeding nutrients that the animal won't be able to utilize.

In this post I'm going to focus on the fiber portions of forage analysis.  We'll get to protein and energy later.  Fiber in this sense refers to the structural portions of the plant cells.  The compounds that make plant cell walls rigid.  These are also the least digestible compounds in forages, thus they are important in indicating how well animals can use the nutrients in the forage.

The big three fiber categories are neutral detergent fiber (NDF), acid detergent fiber (ADF), and lignin.  NDF and ADF refer to several types of fiber and the names come from how they are analyzed.  The forage sample is 'washed' in a detergent solution, that solution is either of a neutral pH or an acid because of the chemicals used in each 'wash'.   Each of these procedures removes a set or components from the plant material, leaving only specific fiber types.  But what do they represent?

Plant cell components (image from University of Minnesota)

The neutral detergent removes soluble carbohydrates, sugars, etc.  This leaves us with only the cell wall components, lignin+cellulose+hemicellulose.  NDF value is a general indicator of intake ability.  As NDF increases voluntary intake generally goes down.

The ADF procedure removes hemicellulose, leaving only cellulose and lignin.  It is a general indicator of digestibility.  Cellulose is not digested by any mammalian enzymes, only by the microbes in the rumen of cattle and sheep or the hindgut of horses, rabbits, etc.  As ADF increases digestibility goes down.

Finally lignin, which is almost completely indigestible.  As lignin increases so does ADF and NDF, which means that both intake and digestibility go down.

Generally fiber can also be used a general indicators of maturity.  As plant age (maturity) increases the percent lignin and cellulose go up, decreasing the quality of the forage. 

That's fiber in a nutshell, what portions of nutrition do you want to hear about next?

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Carbon and Rotational Grazing

Grazing (Photo credit: EricMagnuson)

I'm a frequent reader of Mother Earth News for the recipes of nothing else.  Today I was rather pleased with this article that talks about how the correct management of cattle grazing patterns can improve soil carbon sequestration.  In some cases more so than leaving the land fallow. 

Mob (high-intensity) grazing is nothing new, but in recent years I've been hearing about it more and more frequently.  Here at the University of Kentucky there have been several studies looking at very high stocking rates on pastures and strip grazing corn.  Do you use high-intensity rotational grazing?  What are your thoughts?

 

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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.

Related articles

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• Guest Post: University Research. What They Do and Why It Matters.