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Does the ratio of ADF in hay limit the availability of other nutrients?

Horse Care
#1

Carbohydrates and protein get absorbed in the small intestine, before the fiber mass moves to the hind gut.

NDF (neutral detergent fiber) is the measurement of total fiber in the hay. ADF (acid detergent fiber) is the measurement of cellulose, lignin, and the other fibers that the horse can’t digest in the hind gut, that gets excreted. So NDF minus ADF is the amount of fiber that can be digested in the hindgut, and reduced to calories there.

So for this reason, a hay with higher ratio of ADF to NDF has fewer calories, less nutrition, and that hay gets a lower feed value rating for that reason.

What I’m wondering about is whether having a higher ratio of ADF has any impact on how well carbs and protein are absorbed in the small intestine. Does higher ADF “trap” the nutrients at all, make them less bioavailable?

For instance, take two batches of hay with the same level of carbs/sugars, that is the same level of WSC. If one hay had significantly higher ADF/NDF ratio, would that mean the hay effectively provided less sugar?

I can’t find an answer easily on the internet. I’m trying to figure it out based on what I already know about hay and digestion, but I can think of reasons for either answer.

#2

You are on the right track. NDF and ADF, as well as other forage lab analyses, only represent the amount of nutrients. To take it a step further you need to look at digestibility of those nutrients. Portions of ADF are indigestible but there is an ADF digestibility coefficient. The truly indigestible part is going to be measured in Acid Detergent Insoluble fractions (fiber, protein, etc).

NDF digestibility is going to be decreased by increasing lignification, which is evident in increased ADF values. As plants mature, greater lignin is found in the cell wall which makes cell wall contents (NDF) less available.

I did a quick lit search and found the follow article which you may find helpful in furthering your understanding of the carbohydrate system.

Miraglia et al. 1999.Studies of apparent digestibility in horses and the use of internal markers. Livestock Production Science. 60: 21.

http://fyi.uwex.edu/forage/files/2014/01/MaturityNDF-FOF.pdf

#3

In a word, yes. If you’ve ever seen horses surviving off stemmy round bales, you can visibly see the effects of the nutritional deficiency. But it also depends on the structure of the plant and how the nutrients are located with the cells.

For example, alfalfa can have an extremely high ADF if the stem has matured. But if there are still a lot of leaves on that alfalfa, the overall nutrient quality is not as significantly impacted, since the leaf cells are not composed of as many indigestible structural carbohydrates. Yet you could purchase a grass hay with the same ADF and those indigestible structural carbohydrates are going to be found throughout a greater majority of the plant.

There’s also the matter of where exactly the nutrients are located within the plant. The numbers on a hay analysis are percentages of a core sample, which will include stem, leaves, internal structures, possibly seed heads, etc. Just like with the examples given above between different species, different parts of the plant have different concentrations of macromolecules. Depending on the plant, the majority of the “protein” or “sugar” may not be within the most lignified cells.

Another factor is mastication. Mastication releases the contents of many cells, otherwise almost nothing would be available to be absorbed by the horse until microbial fermentation. A horse who is a thorough chewer is going to disrupt more of those cell walls, releasing more cell contents for absorption.

High ADF/NDF are not a good thing. High percentages of detergent fibers have been linked to impaction colic. Attempting to reduce sugar intake by seeking out high NDF/ADF hay is a much riskier proposition than just purchasing low sugar hay.

#4

Maybe I’m wrong, but I’ve always understood ADF to be a measurement of the lignin content in forage…an indication of the maturity of the plant when it was cut. I always understood NDF to be measurement of the hemi-cellulose or thickness of the plant cell wall.

ADF determines palatability and NDF determines consumption. The more mature the plant is, the higher the lignin content and the thicker the stalk.

#5

[QUOTE=Brian;8500565]
Maybe I’m wrong, but I’ve always understood ADF to be a measurement of the lignin content in forage…an indication of the maturity of the plant when it was cut. I always understood NDF to be measurement of the hemi-cellulose or thickness of the plant cell wall.

ADF determines palatability and NDF determines consumption. The more mature the plant is, the higher the lignin content and the thicker the stalk.[/QUOTE]

NDF measures the total fibre in the hay, including both the fiber that the horse can digest in the hind gut, and the fiber the horse probably cannot digest in the hind gut (lignin, cellulose, silica). ADF measures the fiber that the horse cannot digest, so the ADF number is going to always be smaller than the NDF number. The bigger the gap between NDF and ADF, the more digestible fiber in the hay.

#6

[QUOTE=Brian;8500565]
Maybe I’m wrong, but I’ve always understood ADF to be a measurement of the lignin content in forage…an indication of the maturity of the plant when it was cut. I always understood NDF to be measurement of the hemi-cellulose or thickness of the plant cell wall.

ADF determines palatability and NDF determines consumption. The more mature the plant is, the higher the lignin content and the thicker the stalk.[/QUOTE]

I wrote a nice long post and the computer ate it. :sigh:

Essentially what you are saying is correct, but ADF and NDF are not just palatability and consumption, respectively.

Horses don’t prefer high ADF hay because the high lignin/cellulose/silica content makes it difficult to chew. The amounts of these structural carbohydrates increase as the plant ages. The acid detergent fibers are essentially useless to the horse and the microbes in the gut. Any nutrients embedded within the cell wall or trapped within the contents of intact cells pass through the horse unused.

The NDF component is what will be mostly broken down during microbial fermentation in the cecum (hemicellulose, etc.). A large amount of hemicelluose does usually mean a thicker cell wall on many of the cells, but acid detergent fibers also thicken it, and different cells have different cell wall composition. The reason horses consume less hay when the NDF is high is because their gut stays full with a lot of undigested bulk while it is awaiting fermentation. In the cecum, the neutral detergent fiber will be turned into VFAs absorbed by the horse. But any proteins or simple sugars embedded in the cell wall or in the cell contents of intact cells won’t be absorbed the horse. They are either utilized by the microbes or pass through.

I hope this clears up how everything is related.

#7

That’s nice and clear! Thanks!

#8

Before someone chews me out for poor word choice, when I say the ADF component is “useless,” I meant nutrionally. Physiologically, a small amount is necessary to provide that scratch factor that keeps everything moving on its way out of the horse. But too much is not a good thing.

#9

[QUOTE=Scribbler;8500772]
NDF measures the total fibre in the hay, including both the fiber that the horse can digest in the hind gut, and the fiber the horse probably cannot digest in the hind gut (lignin, cellulose, silica). ADF measures the fiber that the horse cannot digest, so the ADF number is going to always be smaller than the NDF number. The bigger the gap between NDF and ADF, the more digestible fiber in the hay.[/QUOTE]

I get the differences. What I’m not getting is the NDF-ADF=digestible fiber formula. Here are figures from two actual hay tests I have on file.

What you are saying is that a forage with an NDF of 59.57% and ADF of 38.87% (difference of 20.7%) would have more digestible fiber than a forage with an NDF% of 51.05% and an ADF of 33.64% (difference of 17.41%).

You stated, “ADF measures the fiber that the horse cannot digest…” Which I understand and agree. But the results above using your formula contradict that statement.

[QUOTE=Texarkana;8500772]
The NDF component is what will be mostly broken down during microbial fermentation in the cecum (hemicellulose, etc.). A large amount of hemicelluose does usually mean a thicker cell wall on many of the cells, but acid detergent fibers also thicken it, and different cells have different cell wall composition. The reason horses consume less hay when the NDF is high is because their gut stays full with a lot of undigested bulk while it is awaiting fermentation. [/QUOTE]

The proverbial “hay belly” look.

[QUOTE=Texarkana;8500772]
In the cecum, the neutral detergent fiber will be turned into VFAs absorbed by the horse. But any proteins or simple sugars embedded in the cell wall or in the cell contents of intact cells won’t be absorbed the horse. They are either utilized by the microbes or pass through.[/QUOTE]

So why is protein from forage included while calculating protein requirements in horses?

#10

Yes, but remember, fiber isn’t the only component in hay. Hay with a low NDF has less “cell wall” and more “cell contents.” Those cell contents include macromolecules actually digested by enzymatic processes in the horse, like proteins, starches, and sugars.

Regarding the two hay analyses for the sake of discussion, the first hay would provide more of a slow release of energy, but at the cost of losing some nutrition due to the higher NDF/ADF. A horse would likely receive more overall calories and nutrition from the second hay because the fiber portion is lower. Although all of this is speculative not knowing anything else about the two hays except their fiber content.

So why is protein from forage included while calculating protein requirements in horses?

Because mastication releases a lot of it. When horses chew, they mechanically rip open many of the cells, releasing nutrients.

Also, every cell in a plant is not identical. Different tissues have different composition. For example, the vascular tissues that transport water and nutrients tend to be thick and lignified… these tissues make up what we think of as the “stem.” Where as many of the tissues of leaves lack such a thick cell wall and are more easily broken down and digested. Some nutrients are also able to pass through the cell wall/cell membranes of the plant when rehydrated, although I’m not sure if any amino acids are ever small enough to do that.

But the CP you see on a hay analysis is called “crude protein” for a reason. It tells you what’s in the hay, but it makes no promises of what the animal receives. Luckily for us, evolution has made horses extremely efficient at getting most of the stuff they need out of plants.

#11

Tex - :applause: :applause: What a great science lesson this morning!

#12

Yes indeed, thank you!!

#13

Why is there a difference in release rate? Or is it because of the higher ADF/NDF that it just takes longer to digest?

As far as protein goes, I was under the impression that Lysine was about the only or primary amino acid found in forages, in particular legumes. And the absorption or usage was dependent on the balance. Meaning that the utilization of Lysine would be dependent on the amount of available Methionine, Cystine, Threonine, Tryptophan, etc…

When buying hay, I’ve always placed a higher priority on ADF & NDF for the purpose of having the hay provide the majority, if not all of the calorie or energy requirements of our horses. We probably pay more for our hay than most, but in the long run, it’s significantly cheaper than buying calories from bag. Not to mention, savings on vet bills, supplements, etc… For the nutritional requirements, we use a RB.

Thanks for your input.

#14

Grass hays tend to be higher in methionine and lower in lysine, and legumes are the opposite.

You’re right about the hierarchy being important. But lysine is the first limiting AA. Protein synthesis is limited to how much lysine there is. Next is threonine, and so on down the line

#15

This.

The majority of fiber cannot be digested until it reaches the cecum and undergoes bacterial fermentation. It takes several hours for forage just to reach the cecum and over a day to complete the entire fermentation process.

Other macromolecules, such as sugars, starches, and proteins, undergo enzymatic digestion in the foregut and are available to the horse in a matter of minutes or hours.

So the higher the (digestible) fiber content, the longer it will take for the horse to receive energy from the hay.

As far as protein goes, I was under the impression that Lysine was about the only or primary amino acid found in forages, in particular legumes. And the absorption or usage was dependent on the balance. Meaning that the utilization of Lysine would be dependent on the amount of available Methionine, Cystine, Threonine, Tryptophan, etc…

Lysine receives so much attention because it is an essential amino acid that is synthesized by plants, but not animals. Lysine availability in the diet can limit protein synthesis by the animal. But it’s not the only amino acid found in plants. Plants synthesize a broad range of amino acids, and they use them to synthesize many complex proteins to carry out cell functions. Although I’m going to hit the ceiling of my biochemistry education fairly quickly on this topic. :wink:

When buying hay, I’ve always placed a higher priority on ADF & NDF for the purpose of having the hay provide the majority, if not all of the calorie or energy requirements of our horses. We probably pay more for our hay than most, but in the long run, it’s significantly cheaper than buying calories from bag. Not to mention, savings on vet bills, supplements, etc… For the nutritional requirements, we use a RB.

Thanks for your input.

I do the same thing!

#16

If [what-ever plant the hay is made of] is old enough to be stemmy and of poor digestibility, wouldn’t many important nutrients be missing to start with?

I would think this type of hay might fall into the category of “it takes more out of the horse to digest than it gives the horse”.

#17

Yes csaper (I still want to call you casper LOL) that is true. That type of hay often leads to a hay belly - mal-nourishment along with too much indigestible fiber.

#18

[QUOTE=csaper58;8501478]
If [what-ever plant the hay is made of] is old enough to be stemmy and of poor digestibility, wouldn’t many important nutrients be missing to start with?

I would think this type of hay might fall into the category of “it takes more out of the horse to digest than it gives the horse”.[/QUOTE]

I think unfortunately, a number of boarding barns and/or horse owners try to correct poor quality hay with a commercial bagged feed or cereal grain. And when that doesn’t work, they turn to a supplement or multiple supplements in search of a solution. Personally, I’ve never seen a skinny (aka hard keeper) horse on a free choice diet of high quality forage. However, I have seen a number of skinny horses that were fed poor quality forage, several pounds of grain per day, and a list of supplements as long as your arm.

Generally speaking, IMO, poor quality or high ADF/NDF hay is the “root” of most health problems in the horse.

#19

I hear you, I left one barn because the ‘hay’ my young, growing horse was being fed was the bush hogged trimmings from an empty field. Mostly briars, rag weed, and other trash rolled into a round bale.

But not all horses can eat premium hay and be healthy, and now the same horse has an air fern metabolism, and needs hay that is the equivalent of iceberg lettuce.

I also think many barn owners struggle to find good hay. Wonderful hay fields are turning into subdivisions, and hay making is a dying art that few if any young people want to learn. Therefore, good hay can be scarce and is priced accordingly.

Finally, IMO, the sugar content of hay is as, or more, important to the horse’s health than the fiber content.

#20

So what is considered high NDF/ADF? I have hay that is 51%/35%. Is that good or bad?

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