Articles on forages, animals, and grazing systems
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Extension Forage Specialist
University of Kentucky
Phone: (859) 257-3358
Fax: (859) 323-1952
Pastures were slow to green-up with the cool weather this spring. However, the past few days of warm weather has really made the grass pop. I noticed today, April 18, that some of the timothy and bluegrass was beginning to flower. Now is a good time to be investigating pasture stands for legume content.
Legumes are recommended additions to our tall fescue-based pastures. The inclusion of legumes dilutes the endophyte and its negative impact on performance. In addition, legumes improve forage quality as they tend to be higher in crude protein and often digestibility. Legumes also provide an opportunity for bacteria attached to their root system to capture and utilize atmospheric nitrogen. This nitrogen fixation process lowers the need for fertilizer sources of nitrogen.
The addition of legumes into existing pastures is often accomplished by interseeding red and/or white clover. Some will utilize other legumes like alfalfa, lespedeza, birdsfoot trefoil, and others. However, the ease of frost seeding clovers and their ability to thrive in less than ideal soil conditions makes them the preferred legumes. Many producers will frost seed a few pounds to the acre of red clover in February. It is an economical method of interseeding and improving forage stands. Additional information on frost seeding can be found in previous newsletters or at the Master Grazer website http://www2.ca.uky.edu/grazer/ .
Establishing legumes into pastures is not without risk, though the risk is minimal. Legumes can induce a rumen disorder referred to as frothy bloat. This typically occurs when cattle selectively graze legumes from the pasture in high proportions or when the stand is dominated by legumes. Pastures that contain in excess of 50% legumes have an increased risk of inducing bloat. The most prominent bloat inducing legumes in Kentucky are white clover, alfalfa and red clover.
In recent years, bloat losses have been largely associated with white clover. The drought conditions led to a weakening of the pasture, lowering competition and providing an opportunity for white clover to establish and thrive. In many cases the white clover began to dominate the stand making up in excess of 50% of the forage allowing cattle to selectively graze and consume mostly clover. The microbial population in the rumen responsible for digesting the forages are thought to produce a bacterial slime when a large percentage of their diet is fresh legumes. This slime captures or traps the gas released from the fermentation of the forage forming a froth layer in the rumen. This froth prevents the animal from being able to eructate or belch and release the gaseous products. As fermentation continues, more and more gas builds up in the rumen. Eventually, the rumen begins to press against the diaphragm causing labored breathing and eventually suffocation if not corrected.
Legume bloat can be managed. Commercial feed additives can be utilized and have been shown to be effective in reducing the severity and incidence of bloat. These feed additives must be consumed at the target levels daily to be effective.
Poloxalene is the active ingredient in the bloat prevention blocks and feed products. It is also the active ingredient in the commonly used drench product. This detergent-type additive breaks up the foam layer and allows the gas to escape.
Monensin has been shown to aid in controlling forage induced bloat as well. Oklahoma researchers have demonstrated monensin to be quite effective at preventing wheat pasture bloat which is similar to that caused by legumes. Monensin lowers the formation of the foam layer in laboratory settings by selectively inhibiting the growth of some bacterial species in the rumen. However, the product label does not claim to lower the severity or incidence of bloat.
General management changes can be made to lower the risk of bloat as well. Avoid turning cattle on to pastures with a high proportion of legumes when hungry. Allowing legumes to mature to flowering can lower the risk. When possible, avoid grazing legumes that have moisture on their leaves following a rain or heavy dew. Offering a leafy, highly palatable, grass hay is recommended as well. Routinely check cattle as bloat symptoms occur rapidly and death losses may occur as quickly as 3-4 hours after consuming a large amount of legumes. This fall pasture renovation may be required to establish grasses back into the stand. A variety of options exist and you should contact your county Extension office for additional details on pasture renovation. The last straw may be to eliminate the legume from the stand to lower the competition level and provide the grass an opportunity to reestablish. Once the grass has been reestablished, legumes can be introduced into the stand again. Maintaining 30-40% legumes in the pasture is a good target allowing for the improved performance, nitrogen benefit, and minimal bloat risk.
Get out in the fields now and assess your pastures. If you have a lot of legumes in your stands, develop and implement management strategies to reduce livestock losses. For additional information, considering reading Managing Legume Induced Bloat in Cattle as well as visiting your local Extension office.