He had recently turned the herd out onto fresh spring pasture after months in the barn on alfalfa hay. The symptoms looked like grass tetany, but the cows weren’t responding quickly to the IV. The next questions came quickly: What did I think? What to do about these cows? And, what to do about the rest of the herd?
The background: The farm was a grass-based dairy with minimal grain input. The Jersey cows were more than 230 days in milk, averaging 41 pounds of milk per day. The animals had been housed in the barns all winter and fed mostly alfalfa hay plus 8 to 9 pounds of grain daily.
The grain was a 12 percent custom mix of corn, barley, soybean meal, vitamins and minerals, including salt. The spring grass had started to grow a couple of weeks earlier, but the farmer, a skilled grazier, had appropriately kept his cows off the fields until the ground was drier and the grass properly ready to graze.
The pasture: The field was an excellent spring pasture. The farmer had replanted it six months earlier with improved cultivars of Italian and perennial ryegrasses, orchardgrass, festulolium, plantain, chicory and a couple of clovers. It was too early in the spring for the legumes to grow, so the forage was mostly grass and some herbs. In terms of grazing management, cows entered the field at a forage mass of 2,500 pounds and left it with a residual mass of around 1,200 pounds. This is good intensive grazing. And for the soil scientists among us, the soil pH was around 6.0, with 4 percent organic matter and excellent levels of phosphorus and potassium.
The timeline: The cows were turned out on a Wednesday in late March. By the following Monday, three cows were down. Some trembling, but no fever.
The farmer immediately called his veterinarian. Good call – always a solid first step. Since the cows exhibited no fever, the veterinarian ruled out infectious disease. Milk fever was also out, as these animals were well into lactation. But some obvious features pointed to a different syndrome: young grass pasture, early spring growth, well-fertilized with nitrogen – the pasture presented the classic scenario for “grass tetany” (hypomagnesemia, magnesium tetany).
The veterinarian drove out to the farm and administered an intravenous solution of CMPK, a standard IV treatment primarily containing calcium, magnesium, phosphorus, potassium and dextrose. The cows immediately looked better, but the next day, they were still not well. That’s when I got the call.
After listening to the background story, I asked about the pasture. I was basically familiar with the field as I had walked through it a number of times over the past few years. But the farmer quickly used the internet, and he emailed me two forage test reports: the pasture and the alfalfa hay. A few days before turning the cows out, he had walked through that field, taken a forage sample and submitted it to his favorite lab. Good thinking. In fact, he took the sample very cleverly; he used the “grab sample” technique.
It’s not highly sophisticated, but in reality, it is an excellent practical technique for trying to duplicate what a cow would eat. The farmer walked through the field, made believe that he was a cow, and grabbed 20 or 30 handfuls of forage to duplicate a cow grabbing with its mouth. No, it’s not a random sample of all the forage. He wasn’t trying to estimate the average nutritional value of the entire pasture, he was trying to duplicate the intake of a cow who strives to eat the best stuff first.
I looked closely at the forage report. Initially I focused on the minerals, particularly magnesium (Mg). Hmmm. The forage magnesium was 0.26 percent, which is actually fairly high. That was strange. A rule of thumb is the risk of magnesium tetany is moderate for forage Mg levels between 0.12 and 0.18 percent and high for levels below 0.12 percent. This pasture’s Mg level was well above those numbers. (All values are on a dry matter basis.)
I ran a separate check on that forage using a formula called the “tetany ratio.” Magnesium tetany is a complex syndrome involving magnesium, potassium and calcium (also salt, but the cows were getting plenty of NaCl in their grain mix). The tetany ratio is a formula containing these three minerals, and it’s a good tool for assessing the risk of magnesium tetany, especially for forages with marginal magnesium. A ratio higher than 2.2 indicates a high-risk forage. In this pasture, the potassium and calcium levels were 2.69 percent and 0.81 percent, respectively. Although the Mg level of this pasture was not marginal, I thought: No harm in running the numbers. The result was 1.11. No risk there.
What about milk fever? Well, these girls had been milking for more than 230 days. Forage calcium was reasonable at 0.81 percent. No, milk fever was not the issue.
Then two things in this forage report caught my eye: fiber levels and sugar levels. The pasture NDF (neutral detergent fiber) and ADF (acid detergent fiber) values were 29.9 percent and 18.5 percent, respectively. These are incredibly low for young spring grass, which commonly shows fiber levels around 40 percent for NDF and 25 percent for ADF. (Grasses nearly always contain more fiber than legumes like alfalfa.) But the sugar and starch levels were through the roof. Sugar levels were 21.7 percent and starch was 7.1 percent. The meaning was clear: That pasture had extremely high levels of quickly fermentable carbohydrates (starch + sugar = 28.8 percent of the dry matter).
Compare these numbers to the alfalfa hay that had been fed previously to the cows in the barn. The NDF, ADF, sugar and starch values of this hay were 24.5 percent, 22.6 percent, 12.9 percent and 4.1 percent, respectively. These fiber levels were what you’d expect for good dairy-quality hay, and its combined level of quickly fermentable carbohydrates was only 17 percent (= 12.9 + 4.1).
(The crude protein levels of the alfalfa and pasture were 22.7 percent and 15.4 percent, respectively, but these numbers were not important in this situation.)
Recall that the cows were already receiving a daily amount of 8 to 9 pounds of a grain mix, which effectively contains more than 50 percent quickly fermentable carbohydrates like starch and sugar.
A clear story was beginning to take shape. The problem wasn’t magnesium tetany, it was acidosis. On a grass pasture. Wow! Who would have expected that?
Acidosis is a problem in ruminants where too much quickly fermentable substrates like starch and sugar ferment too quickly. The unusually high levels of starch and sugar in this pasture, combined with the high levels of starch and sugar in the grain mix, set the stage. The products of rumen fermentation are acids. In acidosis, the rumen bacteria produce too much acid too fast. This acid overwhelms the buffering capacity of the rumen, rumen pH drops, extra acid crosses into the blood and lowers blood pH. Then real serious problems occur: The animal suffers the symptoms of acidosis.
In this case, however, the question was what can we do now? Well, basically, add something into the feed to increase its buffering capacity, like a buffer such as sodium bicarbonate (affectionately known as “bicarb”). This we did on two levels: firstly, the farmer’s nutritionist reformulated the grain mixture to include some additional bicarbonate and also increased the fiber a bit. And secondly, the farmer put out a free-choice lick of sodium bicarb right in the pasture, letting the cows lick as much as they wanted.
The result? The symptoms quickly disappeared. The cows seemed to recover. Grazing continued unabated. The sun came out, the prices went up, music filled the air and birds smiled. All was copacetic.
But let’s move beyond the details of this case and look at the bigger issue. When faced with a potentially major problem, at least nutritionally, it may be imprudent to leap to the first conclusion based on the initial appearances. The initial conclusion seemed obvious, but it wasn’t. The real issue was buried in the numbers. The forage report was critical, and it wasn’t until the numbers were parsed into meaningful comparisons did the real nutritional problem become apparent. Data, data, data.
This was not just a cow issue. It was a nutritional issue with lessons for all of us. It was a story of stepping back, looking under the hood and following the data, despite initial impressions. A good lesson in many fields, not just grazing. The devil, as they say, was in the data. 
PHOTO: A real-world scenario on a grazing dairy shows, at least nutritionally, it may be imprudent to leap to the first conclusion when health problems appear. The forage report is critical for meaningful comparisons to reveal nutritional issues. Photo by Mike Dixon.
Woody Lane, Ph.D., is a livestock nutritionist and forage specialist in Roseburg, Oregon. He operates an independent consulting business and teaches workshops across the U.S. and Canada. His book, From The Feed Trough: Essays and Insights on Livestock Nutrition in a Complex World, is available through Woody Lane Livestock Services.
-
Woody Lane, Ph.D.
- Lane Livestock Services
- Roseburg, Oregon
