Kern rebecca
Animal Scientist / Ward Laboratories Inc.

Bloat can cause sudden and unexpected death in cattle. When the rumen is unable to expel gases produced as byproducts of rumen fermentation, the rumen expands, pushing on the diaphragm. This pressure on the diaphragm can inhibit the lungs’ ability to take in and distribute oxygen and the animal ultimately succumbs to suffocation. Bloating is a common issue when grazing alfalfa. Pasture bloat is characterized by the foamy rumen contents.

In the rumen

Alfalfa is a high-quality forage providing a high concentration of protein as well as energy. However, this is also what makes grazing alfalfa a bloat risk. Once the highly available or soluble protein and short-chain carbohydrates (think sugars) hit the rumen, microbes go bananas. Legume forages are mostly leafy. Therefore, they are lacking in fiber and lignin, which slow the microbial process of colonizing and breaking down forage particles. So rumen microbes are provided with an abundance of nutrients. The microbes use soluble protein and simple carbohydrates to produce a slimy byproduct. This slimy byproduct entraps gases produced by microbes. These gases would normally escape the rumen through belches. But instead, the gases are caught in the foam and the rumen becomes distended.

Tips for grazing alfalfa

Unfortunately, the only way to avoid all risk of pasture bloat is to avoid grazing alfalfa altogether. However, sometimes circumstances force producers into utilizing forages in ways that aren’t always preferable. Circumstances including drought, armyworms and lack of forage availability can push producers into grazing alfalfa. So if you find yourself with few options, here are some tips to reduce pasture bloat risk: 

  1. Fill cattle up on grass hay or allow them a full day grazing a grass pasture before moving them on to an alfalfa stand. Hungry cattle are more likely to overindulge and bloat.
  2. Acclimate cattle slowly by only allowing access to an alfalfa stand for grazing a few hours a day. Gradually increase time on the stand.
  3. Graze alfalfa in late bloom. Early bloom is the highest risk for developing bloat from grazing alfalfa. At this growth stage, soluble proteins and available carbohydrates are at their peak. As plants mature, cell walls increase along with lignin levels. Higher fiber and lignin content of the forage will slow microbial breakdown, thereby preventing bloating.
  4. Never graze after a frost. Frost ruptures cells, releasing soluble proteins and carbohydrates. The already broken-down cell walls allow easier access to the rumen microbes. Without the fibrous barrier or the plant cell walls, microbes can produce their slime even quicker.
  5. Supplement with poloxalene. This surfactant breaks up soluble protein froth and prevents pasture bloating. It can be offered to grazing cattle through a lick tub. However, individual consumption can be variable, so it cannot be your only strategy for legume bloat mitigation.
  6. Plant "bloat-free" varieties or alternative legume species for emergency grazing. While bloat-free" varieties of alfalfa are not 100% effective, they do reduce bloat risk. Taking this a step further, planting alternative legume species may be the best option. One such alternative which has gained popularity in Western states is sainfoin. Many producers who I have spoken with about this unique forage brag about how they can graze it without bloat risk. This is because sainfoin contains tannins. Tannins precipitate soluble protein and prevent the accumulation of slimy froth in the rumen. 
  7. Observe animals when moved onto an alfalfa paddock. If you see signs of discomfort such as belly kicking, stomping of feet, labored breathing or even a large left side, call the vet immediately.

In conclusion, grazing alfalfa is certainly not an ideal situation to be in as a beef producer. However, when the situation does arise, there are strategies you can implement to lower your risk of pasture bloat. Unfortunately, there is no number on a forage report that can tell you a stand is “safe” from bloat risk. Unlike nitrates or prussic acid, bloat caused by alfalfa is the result of several characteristics of the forage as well as surrounding circumstances.