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

[Texarkana]

[QUOTE=pheasantknoll;8502146]
So what is considered high NDF/ADF? I have hay that is 51%/35%. Is that good or bad?[/QUOTE]

Those numbers are very good.

It’s usually recommended horse owners purchase hay <65% NDF and <45% ADF… the lower the numbers, the higher the quality. Also, you ideally want to see a decent gap between the NDF to ADF. Occasionally you see hay where the NDF is lower than average to the point where it is near equal a high ADF value… like in poor quality alfalfa that has lost most of its leaves.

There are numerous references in literature linking hay of any variety with an NDF >65% to impaction colic. With that said, a lot of grass varieties (at least what I see in my region) will almost always have an NDF in the upper 60s. I never used to see such ubiquitous high NDF values when I lived in PA.

An ADF/NDF that is too low can be a bad thing as well, but it’s rare (impossible?) to find hay that is “too low” in fiber. The more common scenario is that barns invest in high quality hay, but then are stingy feeding it, creating a human-induced lack of fiber.

[Katy_Watts]

[QUOTE=Texarkana;8501408]

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.[/QUOTE]

Have always wonder this: if NSC are found inside the cell wall, and the cell wall is not fermented until it gets to the cecum, how can we assume that sugar and starch are absorbed sooner? I looked long and hard, and I could never find studies that looked at percentage of cell walls broken by mastication by horses. They have done studies on cows and a lot of cells are intact, in spite of rumination. This causes fructans in live grass to convert to sugars inside the cow. We’ve all seen horses that gobble hay and grass. I can’t believe that all the cell walls get broken. Wouldn’t this cause sugars, starch and/or fructans to be released IN the cecum?

[Brian]

Here’s some good reading about selecting hay for your horses…

https://www.agry.purdue.edu/ext/forages/publications/ID-190.htm

[Katy_Watts]

Some plant physiology trivia: Rubisco is the enzyme that fixes carbon in plants. It comprises a lot of the protein found in green plants. As plants turn brown, this enzyme/protein degrades. So old brown grass is generally lower in protein.

As grass and alfalfa age, ADF goes up.But if NSC accumulated BEFORE all the Rubisco degraded, it can still be there. So old dead grass that is low in protein might still be high in NSC if growing conditions were conducive. The ratio of fiber has nothing to do with it. Nutritionists always say mature grass is lower in ‘nutrients’, but that is a carryover from days when they focused on protein content and didn’t test for NSC.

[Brian]

[QUOTE=Katy Watts;8502671]
Some plant physiology trivia: Rubisco is the enzyme that fixes carbon in plants. It comprises a lot of the protein found in green plants. As plants turn brown, this enzyme/protein degrades. So old brown grass is generally lower in protein.

As grass and alfalfa age, ADF goes up.But if NSC accumulated BEFORE all the Rubisco degraded, it can still be there. So old dead grass that is low in protein might still be high in NSC if growing conditions were conducive. The ratio of fiber has nothing to do with it. Nutritionists always say mature grass is lower in ‘nutrients’, but that is a carryover from days when they focused on protein content and didn’t test for NSC.[/QUOTE]

We’ve always tried to feed a young cut, 50:50 alfalfa/grass mixed hay. Ideally, with an ADF in the very low 30’s. Primarily because of the caloric value and also to minimize fructan levels found in cold season grasses grown in our region.

Is WSC-ESC a good method for determining fructan levels?

(apologies in advance if this is too far off topic)

[Katy_Watts]

@Brian;8502696

Is WSC-ESC a good method for determining fructan levels?

The people at USDA that are assigned to developing new testing methods cringe when you ask this. It’s totally dependent on the type of forage, even down to species, variety, maturity and growing conditions. Different fractions bind to the fiber. This makes any calculation that uses subtraction inherently inaccurate. But it’s the best we have at this time. If you ask any lab what their testing error is, you start to realize that we have to take all results with a grain of salt. Sampling error is even bigger.

[Brian]

[QUOTE=Katy Watts;8502655]
Have always wonder this: if NSC are found inside the cell wall, and the cell wall is not fermented until it gets to the cecum, how can we assume that sugar and starch are absorbed sooner? I looked long and hard, and I could never find studies that looked at percentage of cell walls broken by mastication by horses. They have done studies on cows and a lot of cells are intact, in spite of rumination. This causes fructans in live grass to convert to sugars inside the cow. We’ve all seen horses that gobble hay and grass. I can’t believe that all the cell walls get broken. Wouldn’t this cause sugars, starch and/or fructans to be released IN the cecum?[/QUOTE]

If lactic acid is a byproduct of sugar/starch/fructan fermentation in the cecum, and lactic acid lowers pH, wouldn’t fecal pH be an indicator?

[mronthebit]

In response to the original poster’s question the hay with higher levels of ADF and NDF will have less digestible nutrients…ie lower levels of non-fibre carbohydrates even if WSC levels are the same because WSC makes up only a small part of NFC. There’s a chart at Dairyland Laboratories that makes this concept easy to understand…I’m not savvy enough to figure out how to import the chart to this page but I’d encourage anyone who can to go over to their site and have a look.

[mronthebit]

http://https://www.dairylandlabs.net/feed-and-forage/understanding-your-results/wsc-water-soluble-carbohydrates

Figured out how to get the link downloaded. Hope this helps!

[Texarkana]

[QUOTE=Katy Watts;8502655]
Have always wonder this: if NSC are found inside the cell wall, and the cell wall is not fermented until it gets to the cecum, how can we assume that sugar and starch are absorbed sooner? I looked long and hard, and I could never find studies that looked at percentage of cell walls broken by mastication by horses. They have done studies on cows and a lot of cells are intact, in spite of rumination. This causes fructans in live grass to convert to sugars inside the cow. We’ve all seen horses that gobble hay and grass. I can’t believe that all the cell walls get broken. Wouldn’t this cause sugars, starch and/or fructans to be released IN the cecum?[/QUOTE]

I know your education on this topic far exceeds mine, so I’m not sure I’m qualified to address your question.

But…

My understanding is that it’s a significant percentage of cells disrupted by mastication, but obviously it’s not all of them. I don’t know if the study you’re looking for on mastication in horses exists… we’re all aware that research in equine nutrition is pretty limited compared to food animal research.

A percentage of sugars, startches, and fructans DO get released in the cecum, and there are microbial flora specifically to address them. When the sugar release is minimal, there isn’t the pH shift from lactic acid production. Anything inside intact cells with a thick, lignified secondary cell wall won’t be released. So you’re really just dealing with the release of the contents of unmasticated cells without a secondary cell wall.

Some ions (K, P, Mg I think are the main ones) and a portion of the WSC (monosaccharides, specifically) are small enough to diffuse out of some cells when rehydrated in salvia. It’s the same reason you can soak hay and reduce the sugar content. So even if the cell remains intact prior to fermentation, a portion of the nutrients can still become available to the horse.

But you have raised a question I’ve never considered until now: I always assumed the diffusion of ions and sugars was a function of passive transport/facilitated diffusion, like you would see in a living cell. But how much integrity remains in the grasses’ cell walls and membranes after they are killed and desiccated? Is there degradation over time that increases bioavailability of nutrients? That seems like a really straightforward question that has probably already been investigated a million times, I just never recall seeing an answer one way or another.

[Brian]

[QUOTE=Texarkana;8503015]
I know your education on this topic far exceeds mine, so I’m not sure I’m qualified to address your question.

But…

My understanding is that it’s a significant percentage of cells disrupted by mastication, but obviously it’s not all of them. I don’t know if the study you’re looking for on mastication in horses exists… we’re all aware that research in equine nutrition is pretty limited compared to food animal research.

A percentage of sugars, startches, and fructans DO get released in the cecum, and there are microbial flora specifically to address them. When the sugar release is minimal, there isn’t the pH shift from lactic acid production. Anything inside intact cells with a thick, lignified secondary cell wall won’t be released. So you’re really just dealing with the release of the contents of unmasticated cells without a secondary cell wall.

Some ions (K, P, Mg I think are the main ones) and a portion of the WSC (monosaccharides, specifically) are small enough to diffuse out of some cells when rehydrated in salvia. It’s the same reason you can soak hay and reduce the sugar content. So even if the cell remains intact prior to fermentation, a portion of the nutrients can still become available to the horse.

But you have raised a question I’ve never considered until now: I always assumed the diffusion of ions and sugars was a function of passive transport/facilitated diffusion, like you would see in a living cell. But how much integrity remains in the grasses’ cell walls and membranes after they are killed and desiccated? Is there degradation over time that increases bioavailability of nutrients? That seems like a really straightforward question that has probably already been investigated a million times, I just never recall seeing an answer one way or another.[/QUOTE]

While not scientific, and probably about as accurate as a weight tape…I used a digital soil pH tester to test fecal pH in 18 of our horses over a period of 5 days. Each horse was on the same diet of hay along with 1-2 lbs of a RB, with an exception of one. That particular horse was also getting 1 lb of a performance sweet feed twice a day in addition to his 2 lbs of RB. Coincidence or not, his pH readings were consistently 2/10ths less than the rest of the barn.

[pheasantknoll]

Thanks for everyone, including OP who started this thread. has been super-informative!

[Katy_Watts]

This is on cows. I can’t find anything done on horses.
I’m sure there is a big difference between fresh grass and hay.

The release of intracellular constituents from fresh ryegrass (Lolium perenne L.) during ingestive mastication in dairy cows: effect of intracellular constituent, season and stage of maturity
Boudon, A et al.
Animal Feed Science and Technology , Volume 93 , Issue 3 , 229 - 245

The release of intracellular constituents from fresh ryegrass (Lolium perenne L.) during ingestive mastication in dairy cows: effect of intracellular constituent, season and stage of maturity

Abstract
The objective of the trial was to measure the proportions of intracellular constituents (IC) released during ingestive mastication in dairy cows fed ryegrass (Lolium perenne L.) and to quantify the effect of season (spring versus autumn) and stage of maturity. In each season, four dairy cows fitted with a large ruminal cannula were fed indoors with fresh grass. The grass was cut at 23 and 57 days of regrowth, respectively, for the two periods of spring, and at 34 and 68 days of regrowth for the two periods of autumn. To measure the proportion of IC released, the rumen was emptied and ingestive boli were collected directly at the cardia during 30?min. Three subsamples were rinsed carefully with water and their IC contents compared with the IC contents of grass. The grass was at a vegetative stage and of good quality throughout the trial, with an average pepsin–cellulase organic matter digestibility of 76.6% and a NDF content of 501?g?kg?1 dry matter (DM). The proportion of IC released varied strongly according to the nature of the IC considered (P<0.0001). The intracellular nitrogen was clearly less easily released than the total soluble carbohydrates (34% versus 53% of intake). Considering the intracellular subfractions, the released proportions were lowest for chloroplastic constituents such as protein nitrogen and chlorophyll (22 and 28% of intake, respectively), intermediate for fructans (42%), and highest for small vacuolar molecules such as non protein nitrogen, free sugars and potassium (57.7, 60.8 and 58.2%, respectively). The unit eating time amounted to 25?min?kg?1 DM intake on average and was unaffected by season but increased with increasing stage of maturity according to the length of the pieces of grass fed to the cows. Season or stage of maturity had little effect on the proportions of IC released. When the effects were significant, the proportion of IC released generally followed the same trend as unit eating time.

[Katy_Watts]

[QUOTE=Texarkana;8503015]

But you have raised a question I’ve never considered until now: I always assumed the diffusion of ions and sugars was a function of passive transport/facilitated diffusion, like you would see in a living cell. But how much integrity remains in the grasses’ cell walls and membranes after they are killed and desiccated? Is there degradation over time that increases bioavailability of nutrients? That seems like a really straightforward question that has probably already been investigated a million times, I just never recall seeing an answer one way or another.[/QUOTE]

Nutrients don’t leak out of living cells. Nutrients move between cells, but there is a waxy cuticle layer on the outside to prevent leakage. The thickness of this protective layer depends on species and previous adaptation by the plant.

Yes, seems a very straight forward question, but I can’t find the answer for horses.

[Texarkana]

[QUOTE=Katy Watts;8503396]
Nutrients don’t leak out of living cells. Nutrients move between cells, but there is a waxy cuticle layer on the outside to prevent leakage. The thickness of this protective layer depends on species and previous adaptation by the plant.

Yes, seems a very straight forward question, but I can’t find the answer for horses.[/QUOTE]

No, they don’t “leak” but they do travel through the intercellular plasmodesmata. If you disrupt the connections (like when you cut hay), nutrients can indeed diffuse out of cells that are otherwise intact.

ETA: only reading the abstract, the research with cows seems to jive with my own hypothesis on what’s happening. Small molecules (ions, simple sugars) appear to diffuse out of portions of plant that were “disrupted” but maybe not fully masticated. Large macromolecules (proteins, complex carbohydrates) are mostly stuck. Interesting… thanks for sharing!

[Texarkana]

[QUOTE=Brian;8503100]
While not scientific, and probably about as accurate as a weight tape…I used a digital soil pH tester to test fecal pH in 18 of our horses over a period of 5 days. Each horse was on the same diet of hay along with 1-2 lbs of a RB, with an exception of one. That particular horse was also getting 1 lb of a performance sweet feed twice a day in addition to his 2 lbs of RB. Coincidence or not, his pH readings were consistently 2/10ths less than the rest of the barn.[/QUOTE]

You have some dedication, testing manure for 18 horses! :yes:

I don’t think the results are coincidental at all. There is a lot of information out there on sweet feed’s role in acidifying the hindgut. Sweet feed contains more sugars and starches than can be fully digested by enzymatic processes in the foregut-- and significantly more than most hay.