After all these years of information gathering, I have decided that I have enough information to help me calculate the risk of allowing my horses a bit of fall grazing. The experiment begins in November, 2011.
My primary concerns are:
Making sure the horses receive adequate salt: I know that in our area, spring and fall grass will contain an excess of potassium. This I believe to be equal to, or greater than, the danger of excess sugar. While I can’t buffer the effect of excessive sugar, I believe I can offset the risk of the excessive potassium by making absolutely CERTAIN that the horses ingest adequate salt, calcium and magnesium.
It goes without saying that in our high-rainfall area, the sodium in the grass will be dismally low. And I do not trust the horses to ingest enough salt voluntarily to meet their daily needs. This is particularly dangerous in fall and spring when the K (potassium) level is going to be high in the grass.
Excess potassium can fool the horse into believing it actually has enough sodium. This will limit sodium intake and a cascade of evils follow. One of those is disinterest in drinking sufficient water. What a setup for a winter impaction colic! Excessive K disrupts calcium and magnesium metabolism as well.
I try to assure that the horses are receiving adequate salt – about one ounce per day – by sprinkling salted water on their hay. They seem to like the slightly salty hay just fine.
Making sure the horses receive adequate calcium and magnesium:
In the cold weather, it is hard for the grass to take up adequate amounts of these two “heavy” minerals. I have been surprised by my fresh forage analyses that the calcium content of the grass tends to be quite good even in colder weather. Magnesium (Mg) is enough to meet NRC requirements but never quite enough to match the Ca (calcium). We top up calcium and magnesium on the pasture every year but this situation tends to repeat itself, so this year I will be looking for ways to boost the magnesium uptake.
At any rate, based on analysis of their foundation hay, more magnesium wouldn’t hurt a thing, especially when it comes to allowing fall grazing. I top their ration up each day with roughly a tablespoon of dolomite, which contains both calcium and magnesium.
Checking sugar content in the grass with a Brix Refractometer:
This is a Brix refractometer. It is a small, hand held device that is used to measure the amount of sucrose in a liquid. A drop or two of liquid is put on the prism (left end) and the plastic cover is lowered onto the sample. Then the prism is held up to the light to obtain a reading.
The reading looks something like this. We are only interested in the scale on the left, the Brix %
You’ll note that where the blue and white come together, the number on the left hand scale is roughly 17. This suggests that the percent of sugar in the liquid is 17%. That might be the sweetness of a nice, juicy apricot.
To further put this into perspective, I added one teaspoon of table sugar to one cup of distilled water (this is all very unscientific, kitchen chemistry). The Brix reading of the liquid was 2.5%. However, things aren’t so cut and dried, as I was soon to discover.
I added a teaspoon of Morton Lite Salt, which has a high percentage of potassium, to the brew.
The new brix reading was 5%. So it IS true that a Brix refractometer reads other compounds besides sucrose in plant sap.
My first reaction was, well, that is a GOOD thing, because it means the sugar in the grass sap would be LOWER if the refractometer is reading the other minerals. Once again, things were not so cut and dried.
I have in the past, regarded a Brix reading of 3 to be the maximum that I would allow for limited fresh grazing. However, I never quite understood why my inclined-to-be-fat mare gained weight readily on grass of such a low brix reading. The answer became clear as I rummaged through more data.
Fresh Forage Analysis
Here is the fresh forage analysis:
Download 11-11 Fresh Forage Brix 1.5 - 2.0
In order to see if I could correlate the Brix reading to the actual sugar content of the grass, I gathered a sample and sent it in for a quick analysis. Before I sent the sample, I took several Brix readings of the grass sap and came out with an average of 1.5-2%.
In my mathematically challenged brain, I was assuming that a simple sugar content of 1.5-2% Brix meant a super-safe grazing level, right? Wrong again.
Looking at the AS SAMPLED column, I discovered, much to my delight, that the simple sugar value was 1.9%, right in line with my brix reading of 1.5-2%!
But the sugar in the DRY MATTER column was 14%!
How could this possibly be?! I thought long and hard about this, and then thought, hey wait! I was sampling grass sap, not dry hay. Maybe that had something to do with the low-Brix, high DM sugar analysis (high meaning over 10% for at risk horses).
Now my confusion became acute. I had sent in a sample at almost the exact same time last year, so I consulted it. I knew it was of roughly the same Brix reading.
Upon consulting the 2010 report, I discovered that the As Sampled sugar content was 1.42%, and the Dry Matter sugar content was a mere 7.53%. How could the Dry Matter sugar content have DOUBLED when there was such a minor difference in the As Sampled sugar content between the two reports?
You have probably already guessed the answer. The difference is not so much in the SUGAR content of the As Sampled column; it is the amount of DRY MATTER in each sample that made the difference.
The 2011 sample contained 13.7% Dry Matter. The 2010 sample contained 18.87% Dry Matter. That is a difference of 5.17%, apparently enough to send the actual amount of sugar the horse is eating in each bite soaring in the LOWER dry matter sample, the 2011 sample.
By now my brain is a shredded mess, as I try to figure out the correlation, based on the as-sampled values. I am still trying to salvage my Brix reading.
Then, realizing that the lab isn’t testing the wet grass, but the dried grass, it suddenly occurred to me that they are determining the percent sugar in the DRY MATTER CONTENT first, then doing the simple math to get the AS SAMPLED number. What threw me off is that the As Sampled column always comes first.
So, you can run it out on the above analysis:
% Dry Matter Sugar x % Dry Matter = % As Sampled Sugar
.14 x 13.7 = 1.9
It worked on the 2010 test as well, plus the other values that are reported on the tests. Whew, I thought I’d lose my marbles before I figured that out!
Having the as-sampled value first (the Brix %) does us no good without knowing what the dry matter content of the fresh forage is, and knowing the percentage of the sugar in the plant sap does us no good whatever in determining the safety of grazing fresh grass. However, I think I’ll continue to use the refractometer as a tool for checking sugar content, but I think I’ll lower my maximum tolerable Brix to 2%.
GRAZING
After crunching the numbers on the fresh forage analysis against analysis of the hay that forms the foundation of the horses’ ration, I realized that a bit of grazing on the 14% sugar DM grass wasn’t going to add a significant amount of sugar to the horses’ diet.
What worried me more was the high potassium content of the grass. 3.31% is quite high! So I ran the Calcium:Magnesium:Potassium numbers through the Grass Tetany equation and discovered that the grass is still well below the threat threshold, particularly if I assure the sodium, calcium and magnesium values are topped up in their diet. I decide to risk it. The main thing is managing their intake. How, with a grazing muzzle? No, I’m going to try something different – “Management Intensive Grazing,” or perhaps more accurately, “Strip Grazing.”
During my years as a grassfed lamb producer, I read reams of information about Management-Intensive Grazing (MIG). Although I never became proficient at it (I never had enough sheep), I have a good working knowledge of rotational grazing. Plus, I have a considerable amount of idle equipment for rotational grazing with the horses.
I’ve spent a lot of time researching to be able to estimate how much grass a horse will eat in an hour, and the answer as always is, it depends. The averages of how much grass they will eat, and how many hours of grazing it would take to get full nutrition from grazing alone, range from variable to ridiculous to dangerous. We’ve seen that a difference in sap concentration of sugar has no correlation whatever to how much sugar a horse ingests at any given stage of the grass’ life cycle.
So, I had to come up with my own estimate, and decided that I could risk allowing them to graze for 1 ½ hours per day (after accustoming them slowly) on this 2% Brix grass, based on an estimate of 4 pounds of grass eaten per hour. I cannot even begin to fathom the relative good they receive from the grazing, in terms of both nutrition and happiness.
Their foundation hay is very low in sugar (but unfortunately high in K) and four pounds of grass penciled out to be roughly ½ pound of additional dry matter. So I subtracted a pound of hay from their daily ration, and cranked up the salt, calcium and magnesium in their diet. Now the interesting part begins.
In the grazing literature, it seems that cows have a perfectly uncanny instinct for the best grass. Needless to say, that is the un-bitten, un-trampled, un-pooped on grass.
If you give a cow a strip of fresh grass each day, it is unlikely she will need a fence behind her until all the fresh grass along the new strip has been eaten.
Oh my, do we underestimate our horses’ instinct for fresh, virgin grass!
Day after day, as I parcel out a narrow strip of fresh new grass to the horses, they do not leave that strip until the upper 50% or so of the grass has all been nipped!
If I wait too long, they will have wandered back into the already-bitten grass. This is absolutely what we DON’T want. Every time that fresh grass has been bitten ONCE, it needs to be rested until it re-grows. The amount of time it takes for the grass to recover depends of course, on the time of year. In the fall, our grass is growing very slowly, so the horses may never return to the original strip of grass I have given them before the new growing season arrives! If they were allowed to graze in summer, they might return to the original spot in as few as seven days!
One grass plant, one bite. That is the Law of the First Bite, as the graziers call it.
The horses are presently strip-grazing a one-acre paddock, and the grass is about 6-8” tall. I move the fence roughly two feet each day, giving them a new strip of grass about 2 feet wide and 150 feet long. They are uniformly biting off about 4” of the top – the ice cream – then moving on along the fence. If they have gone back to the already-bitten grass, they are starting to eat the cardboard box that the ice cream came in. This we DO NOT want. One reason is because more of the villainous fructan is concentrated in the lower parts of the plant. The other reason is that we want the grass to have enough leaf surface to continue photosynthesizing, so it can strengthen itself and recover.
In addition, keeping adequate cover on the ground helps the water cycle and prevents erosion.
Just because there is grass left, does NOT mean you still have grazing!
The grass should never be bitten lower than about a 3 – 4” “residual.”
So, what I have become quite confident in, is that my two small horses, will “cream” a strip of grass that is roughly 6-8” high, 2 feet wide and about 150 feet long, in about an hour to an hour and a half. Absolutely reliably. If I go out and find them nibbling around in the previously grazed area, I’ll know that I either need to shorten their grazing time or widen their strip. No frustrating grazing muzzles. Just pure joy for an hour and a half a day. How many of us humans enjoy that much happiness!
Interestingly, after having a breakfast of hay before turnout, they seem to be famished after an hour and a half on the watery grass and come in at a gallop for a carrot and a little more dry matter.
Time will tell if I have made a mistake in allowing grazing on the watery fall grass. Like any of us, all I can do is hope I’ve covered all the bases.
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