By Hubert J. Karreman, V.M.D.
Every spring I usually get at least a few calls from alarmed farmers that cows on lush pasture are suffering from, believe it or not, rumen acidosis. Oftentimes graziers will reflexively say that rumen acidosis only occurs on conventional confinement farms, due to the practice of feeding large amounts of grain and insufficient fiber to push for really high milk production. While rumen acidosis is more commonly seen any time of year on farms that feed a combination of high amounts of corn silage, high-moisture corn, and grain supplements fed out as a TMR, believe it or not it can also hit grazing cows that milk more moderate levels of grain feeding.
First, let’s look at what rumen acidosis is. Normal healthy rumen pH should be about 6.8. The pH tells you how much acid is in a system, whether you’re measuring the soil that your crops grow in, your well water, or a cow’s rumen. As the system becomes more acidic, the pH number goes towards zero. The pH is also a “log” number, which means that a one point drop from 6.0 to 5.0 indicates that there is now ten times more acid in the system. The population of microbes in the rumen is highly varied, and each type of bug is sensitive to a certain range of pH. Some of the digestion products the rumen creates are dependent on the general rumen ecology, which is affected by the pH. When all the bugs are “happy,” there will be a lot of production of acetic and propionic acid, with some butyric acid. These are volatile fatty acids that can migrate through the rumen wall and enter the cow’s general system to help build certain milk components (acetic acid, for example, which generally helps build butterfat). When the rumen pH drops much below 6.0, the normal rumen bugs are unhappy and die off, especially if the pH remains too low for too long and then lactic acid–loving bacteria will predominate. Rumen acidosis is then happening, burning the walls of the rumen.
The pH, being a reflection of the amount of acid present, can be changed very easily by the cow’s intake of different feed ingredients. To keep the rumen bugs happy, cows chew cud. Chewing cud creates saliva, which has bicarbonate in it and opposes acid. Therefore, the more the cows chew cud, the more saliva they produce, and this saliva when swallowed with the cud maintains a rumen pH between 6.0 and 7.0, keeping the important microbes happy. What makes cows chew cud? Fiber. The best fiber for cud chewing is dry hay. You can never have enough dry hay on a dairy farm. Dry hay is nearly medicinal feed for cows. Fresh grasses and legumes from pasture also provide a lot of material for cud chewing, but sometimes the effective fiber is not as great. We easily see this when cows shoot “pasture manure” across the walkways at this time of the season.
What is almost the opposite of healthy fiber? Grain. The purpose of grain is primarily to provide energy for cows to make lots of milk. Grain feeding tends to favor propionic acid–producing bugs. Propionic acid is the volatile acid that contributes to higher levels of milk production. In the wild, ruminants do eat grain by way of seed heads on grasses and the like. So while grain is not entirely foreign to a cow’s system, giving too much hammers the system in a terrible way. As grain ferments in the rumen, it produces lactic acid, which will drop the rumen pH lower and lower unless offset by sufficient fiber intake. The whole science of ruminant nutrition essentially boils down to balancing the amount of fiber and grain going into the rumen to keep the bugs happy and to produce milk. How this is accomplished definitely affects cow health.
The health of a cow (or any ruminant) depends on a healthy rumen. A ruminant by definition chews cud. The amount of cud chewing, especially chews per cud, is a quick way to evaluate the health of a cow’s rumen. A cow should chew anywhere from fifty to seventy chews per cud that is brought up. This is easy to watch and fun to do. If there are less than fifty chews per cud on a significant number of animals, their diet is lacking in fiber. If grain is coming through in the manure or the manure is not consistent between herd animals, this will confirm rumen acidosis.
With all this in mind, perhaps you can see how rumen acidosis can occur with grazing herds. In grazing herds that feed grain (which most do to some extent), there must be adequate effective fiber going into the rumen so the cow chews cud as much as possible to maximize saliva production with its bicarbonate. I have seen grazing herds on lush spring grass that get rumen acidosis by “slug feeding” grain twice a day (even as little as six pounds per feeding) at milking times and not consuming dry hay but only baleage, or worse, haylage (short chop). Always feed hay before grain. Never feed grain to cows straight after pasture—it’s way too much highly fermentable starch for the rumen to handle after other rapidly fermentable sugars from pasture are already in the rumen. Always put some kind of forage out first; then feed the grain.
Typical signs of rumen acidosis include decreased or no cud chewing, loose or diarrhea manure, becoming skinny, decreased milk, and possibly teeth grinding. The treatment is rather simple: long-stem dry hay, free-choice or force-fed baking soda (sodium bicarbonate), and rumen probiotics to repopulate the rumen with “good bugs.” This treatment will be needed for a few days until manure stabilizes and appetite improves. If a cow is truly acidotic, she will eagerly eat dry hay to the exclusion of other feeds. Always try to feed the most nutrient-dense forages to cows to keep the rumen healthy and maintain good body condition. At least 60 percent of resting cows should be chewing cud at any time and each cud ideally chewed sixty times.
Watching for Rumen Health
We all know that grazing is more of an art than a science, but just because cows are on green grass it doesn’t necessarily mean that their rumens are happy and healthy. Perhaps one of the best and easiest ways to watch rumen health is to let your cows tell you how they are doing. Do they chew at least sixty chews per cud that they bring up?
It’s easy to do—simply count the chews they chew of a cud right after they bring it up. Do it with a bunch of cows. If chewing less than fifty chews per cud, they are lacking fiber for the rumen mat. That is actually vital biological information to know. Also, are at least 60 percent of the cows chewing cud an hour after eating? What does the manure look like? With good digestive health, manure should not shoot out of cows like water from a hose but instead should “set up.” It also shouldn’t have any whole grain in it.
That’s money going right through your cows without any benefit to you. Truly, feeding stored forage can beautifully balance out lush, green grass quite nicely. By taking some simple steps, you can make sure that your cows are healthy and happy when out on pasture this season.
Source: Four-Seasons Organic Cow Care