Rumen Health in Beef Cattle: Acidosis, What to Watch For, and More
Obvious and less-obvious rumen health indicators to monitor
By Craig Belknap, MS, PAS
As a cattle feeder, what do you think of when you think about rumen health? Most people would probably think about rumen pH, acidosis, and the way feed intakes can “yo-yo” up and down and put rumen health at risk. While those thoughts are certainly accurate, rumen health goes much, much further than these issues alone.
One reason some feel that rumen health is no longer a big issue is due to the widespread availability and usage of high-fiber co-product feeds such as distillers grains and corn gluten feed. After all, these feeds now allow us to get more fiber into the diet without sacrificing energy density and thereby lower the risk of acidosis.
However, there’s more to rumen health than just clinical acidosis. Even if we don’t see the classic signs of acidosis, that doesn’t mean the rumen is operating at peak efficiency. There are numerous issues that can have a negative effect on rumen health and performance, but don’t necessarily cause any clinical symptoms or problems. These “invisible issues” could be related to a subclinical acidosis condition, but could also be unrelated. Therefore, don’t just assume rumen health is “all good” just because you have “enough” fiber in your cattle’s diet. Let’s take a look at the obvious, as well as some not-so-obvious signs that we can tie back to rumen health.
The obvious signs…
In starting or feedlot cattle, acidosis generally means an acidic rumen pH caused by too much rapidly fermentable carbohydrates and/or too little fiber. This situation results in a cascade of events such as death of some rumen microbes and a shift in the microbial balance. Cattle generally go off feed until they feel better, at which time they then overeat, tripping them into an acidosis state once again — hence the “yo-yoing” intakes. The acidotic state in the rumen also causes damage to the rumen lining, which can even lead to bacteria from the rumen actually entering the bloodstream and traveling to the liver, eventually resulting in liver abscesses.
Feedstuff digestibility also decreases in cattle experiencing acidosis. The cause of this is twofold: First, the shift in the rumen microbial population can impair microbial fermentation – especially of fiber. Second, damage to the rumen wall can also decrease nutrient absorption within the rumen.
There are also some other issues such as laminitis, which is generally a result of histimine being released from rumen microbes that die as a result of acidosis. This effect then leads to inflammation that causes a weakening in the laminar structure of the hoof.
Feedlot bloat can also be attributed to rumen health, and is often associated with acidosis conditions as well. Acidosis will result in polysaccharides being produced by dying rumen organisms, thus causing an overproduction of foam, which in turn traps rumen gas and prevents eructation.
Note that most of the items above have one thing in common – acidosis. However, you don’t need to have clinical signs of acidosis in order for it to be costing your operation money. For example, can you see which animals in a pen have a damaged ruminal lining? Which animals may have a liver abscess robbing you of performance? Which animals have a microbial balance that may impair feedstuff digestion?
And, keep in mind that acidosis is about more than just fiber and starch. It’s also about how you transition cattle from one type of feedstuffs to the other. It takes time to acclimate a new microbiome once a diet change occurs. Most clinical and subclinical acidosis issues are not so much about the amount of starch or fiber in the diet – it’s more about diet transition.
The not-so-obvious signs…
Heat stress + fever = uh-oh!
OK – so perhaps for you the obvious signs and discussion are simply a review. What other rumen health issues occur that might not be so obvious? One example involves those dying rumen microbes during a bout with acidosis. When many of those microbes die, they release a compound called lipopolysaccharide (LPS ). LPS is a pro-inflammatory compound, which means it stimulates inflammation within the body. Not only can this inflammation decrease intake and rob the animal of energy that it could otherwise use for growth, it can have other negative effects as well, including fever. All of these effects can be problematic, but when coupled with a summertime battle with heat stress, the effects are magnified. Moreover, acidosis often is worse during heat stress situations and it’s a recipe for disaster. How about a sudden heat stress situation, combined with an LPS-induced fever?
What about those co-product feeds?
Yes – those high-fiber co-product feeds are beneficial when it comes to acidosis. But what about the sulfur? We like to think that we always buy our distillers and gluten from plants that regularly run low in sulfur. But could there ever be an issue – a bad batch or a hot spot? Remember, it’s technically not the sulfur in the gluten or distillers that can cause the biggest problems for your cattle, it’s what the rumen microbes make from the sulfur. Certain rumen microbes have the ability to biochemically reduce the sulfur in feed or water to hydrogen sulfide gas. Hydrogen sulfide is highly toxic to cattle. While some of this chemical conversion is inevitable, the amount increases in animals with a lower rumen pH. Moderating sulfur reduction is just another benefit of maintaining adequate rumen pH.
Antibiotics – friend or foe?
Some classes of antibiotics such as ionophores often have a beneficial effect on many rumen health parameters. However, other common antibiotics such as chlortetracycline or oxytetracycline can have mixed effects. Remember that by definition an antibiotic is a compound that kills or inhibits the growth of microorganisms, particularly bacteria. While this can be a positive effect in an animal that has a bacterial infection, it can also be a negative from the standpoint of impacting the rumen microbes that ferment feed and assimilate protein for the animal.
Research by Chai et al. (1999) showed that cattle given in-feed chlortetracycline at the label-recommended dosage for beef cattle tended to have a decrease (P < 0.10) in ruminal acetate, propionate, and butyrate production. The cattle also tended to have lower total tract neutral detergent fiber (NDF) and organic matter (OM) digestion for the week after chlortetracycline feeding. This potential risk to rumen function should be something to consider before throwing antibiotics into a situation in which they may not be the necessary or best choice of action.
In summary, rumen health is a major issue in feedlot cattle, no matter the level of fiber in the diet and/or any clinical signs of acidosis. Maintaining a rumen that is resilient to challenges is not easy, but the benefits of doing so are great — better overall animal health, performance, well-being, and profitability.
Chai, W., M. F. Montano, and R. A. Zinn. 1999. Immediate and Carryover Effects of Short-Term Therapeutic Feeding of Chlortetracycline on Digestive Function in Feedlot Steers. Proceedings, Western Section, American Society of Animal Science 50:301–305. Available from: https://animalscience.ucdavis.edu/sites/g/files/dgvnsk446/files/faculty/zinn/pdf/03.pdf