Clover is a valued forage crop, offering livestock high protein content and digestibility, which improves animal performance. As a legume, clover fixes atmospheric nitrogen into the soil, reducing the need for synthetic fertilizers in the pasture. However, grazing clover presents a significant management challenge due to the risk of frothy bloat in ruminants. Understanding the conditions that lead to this life-threatening condition and implementing appropriate management practices are necessary for safely incorporating clover into a grazing system.
Understanding the Primary Risk of Clover Grazing
The main danger associated with clover grazing is frothy bloat, a condition where the animal cannot expel fermentation gases from its rumen. This condition is triggered by the rapid consumption of lush, immature legumes, which are high in soluble proteins and low in fiber. The quick breakdown of these plant contents leads to the rapid production of gas in the rumen.
The soluble proteins released from the clover act as foaming agents, trapping the gas in a stable, persistent foam. This stable foam cannot be released through the normal process of belching, or eructation. As fermentation continues, the gas buildup distends the rumen, placing pressure on the animal’s diaphragm, heart, and lungs. If left untreated, this pressure can lead to asphyxia and sudden death, making bloat a serious concern for livestock producers.
Determining Safe Grazing Conditions
Safe grazing relies on timing livestock access based on the plant’s condition and environmental factors. Clover should not be the dominant forage; content exceeding 40% is considered a high-risk scenario. The risk is lower when clover is grazed as part of a mixed sward, ideally comprising 30% to 50% legumes.
Plant maturity also plays a role in safety, as immature, rapidly growing clover has the highest concentration of soluble proteins. Clover in the flowering stage is generally safer to graze than plants in their vegetative, pre-bloom stage. A primary environmental factor is the moisture content of the foliage. Grazing wet clover—such as after heavy dew, rain, or irrigation—significantly increases the bloat risk because wet surfaces allow for quicker release and breakdown of the bloat-causing proteins. It is safer to delay turning out animals until midday when the dew has dried and the plants are less saturated.
Active Management Strategies to Mitigate Risk
Proactive management strategies focus on modifying the animal’s diet and grazing behavior to reduce bloat risk. One effective step is to introduce livestock to clover-rich pastures slowly, allowing rumen microbes time to adapt. It is important to avoid turning out hungry animals onto high-risk pastures, as they are more likely to gorge themselves on the lush forage.
Feeding dry hay or other roughage before introducing animals to the clover field is a common practice. This pre-feeding helps fill the animals and slow their clover intake, while the fiber dilutes the concentration of lush forage in the rumen. Grazing techniques like strip grazing or rotational grazing can also manage the volume of clover consumed and prevent animals from selectively consuming only the most succulent plant tips.
Chemical preventative measures can be used for additional protection to stabilize the rumen environment. Products containing anti-foaming agents, such as poloxalene, can be incorporated into feed, mineral blocks, or drinking water. These surfactants work directly in the rumen to break up the stable foam, allowing trapped fermentation gases to be expelled normally. Ionophores like monensin can also be included in supplements to modify the microbial population and gas production within the rumen.
Specific Considerations for Different Clover Types
The degree of bloat risk varies among common clover types used for forage. Red clover is associated with a higher bloat risk than white clover, particularly during rapid growth early in the season. Red clover also presents a concern for breeding ewes due to its higher concentration of phytoestrogens, which can negatively affect reproductive performance.
White clover is considered a moderate risk, lower than red clover, but requires careful management when it makes up a high percentage of the sward. Specialized varieties of legumes are utilized to minimize the inherent danger of bloat. Certain legumes, such as birdsfoot trefoil and sainfoin, are considered low-risk or bloat-safe because they naturally contain condensed tannins. These tannins bind to the soluble proteins in the rumen, preventing the formation of the stable foam that causes frothy bloat.