| Take home message | Introduction | Management to reduce bloat | Use of bloat control products | Conclusion
This is a fact sheet from the Health Management section of the Alberta Feedlot Management Guide, Second Edition published September 2000. The 1200 page guide is available for purchase on CD-ROM.
Take Home Message
Producers are practicing management intensive grazing of alfalfa and clover based pastures realizing the potential for improved weight gains and economic return. The major downfall of this practice is the losses associated with frothy bloat which can have serious consequences resulting in mortality and decreased production of individual animals. This is especially true of leguminous forages in the early stages of growth.Several alternatives are now available to minimize this hazard but do not replace the vigilant observation necessary when utilizing this high return grazing management.
Introduction
Bloat causes losses to the Canadian cattle industry yearly in the form of mortality and decreased weight gains. In recent years, the potential for economic returns in weight gains when grazing leguminous pastures has prompted advanced means of controlling frothy bloat. Predisposing factors to frothy bloat on pasture are numerous and unpredictable. Cattle grazed on leguminous pastures in the prebloom stage under wet conditions are particularly susceptible. Pastures at this stage are high in protein and water and very low in fibre. Low fibre content in the ruminant diet results in decreased saliva production. Saliva is a natural antifoaming agent. Consequently, with increased protein and water intake and reduced saliva, rumen action generates a large foamy gaseous volume which results in bloat. The potential to develop bloat on pasture is unpredictable due to the regrowth patterns of alfalfa, selective grazing habits of cattle, and changing weather patterns.
Anti-bloat products and key grazing management practices have been combined recently to successfully utilize legume pasture. Varieties of legumes such a sainfoin and birdsfoot trefoil have a minimal bloat incidence, however, their productivity is substantially limited. New varieties of alfalfa are presently being researched, but to date these varieties have not been able to duplicate the gains of the older varieties. The most recent advance has been the development of the LIRD (low initial rate of digestion) Cycle 4 strain by Agriculture Canada. This strain has been found to reduce bloat by approximately 70 - 80% in field trials. Further testing is ongoing.
Management to Reduce Bloat
Because bloat only occurs when there is an excess of fine, low fibre, bloating material in the rumen, it is essential that management of the feed consumed becomes critical. Fibrous feed must be consumed by the animal in conjunction with the bloatable legume material. This can be done by either feeding a hay along side the legume pasture in such a way that the rumen contains some fibre before the animals have access to the youthful, bloatable legume growth, or forcing the animal to consume the coarser parts of the legume plant as well as the fine parts and/or the non bloating plants within the stand. In either strategy, the fine material in the rumen must be diluted with coarser material that stimulates cud chewing and saliva production. Most logically this can be done by using electric fencing and time management coupled with stock density to ensure that the animals are not just selecting the fine bloatable material. This is especially important when the legume plants are youthful and the plant cells are fragile such as after a rain, heavy morning dew, or a recent frost. Bloat often arises from breaks in grazing such as after a storm, attacks from biting insects, and escape from pasture. Uniform and regular intake is the key to minimizing bloat on these pastures. Controlled grazing can eliminate selective grazing. Also, pastures can be grazed when they are past the high risk prebloom stage. The potential for bloat is less at this stage and the plant’s regrowth potential is better. Gains at this stage are only slightly down from those in the prebloom stage. Again it is best that cattle only be moved during the middle of the day when the stand is dry, cattle have coarse feed in their rumens and observation of them is maximum.
Both cattle type and genetic susceptibility can influence bloat incidence. It is thought that susceptibility is a heritable trait, but no scientific studies have been done to substantiate this belief. Some authors believe that bloat prone cattle have a slower rate of liquid passage through their ruminal contents. Cattle which become distended should be removed and culled from that pasture, thereby, removing potential problems.
Use of Bloat Control Products
Several bloat reducing products exist in the market. All of them operate as surfactants that reduce the vicosity of the rumen fluids and reduce bubble formation. Without the ability of the rumen contents to form bubbles, the gases are easily released similar to any other digesting feeds.
Prophylactic bloat treatments are available as ionophores, like Rumensin® or Bovatec®, which alter the rumen’s fermentation (Figure 1).
Figure 1. The fermentation of carbohydrates to volatile fatty acids in the rumen.
This altered fermentation produces more propionic acid and less acetic and butyric acid. Hence, the methane and carbon dioxide gas available for overall gas production is reduced. This directly decreases the potential for bloat. Unfortunately, ensuring adequate consumption on a daily basis is a concern. If trained, cattle can be fed grain with the required daily dose of Rumensin® (250 mg/head). Bovatec® has been tried in the salt/mineral mix at 10%. At this dosage, mature cows need to consume 60 gms/head/day. Bloat Guard® (polaxalene) can also be fed at 1- 2 grams per 100lbs of animal weight. Since its effect only lasts approximately 12 hours, it is better to split this dosage over two feedings. In Canada, poloxalene is sold through feed companies either in mineral or for mixing with grain. In the USA, polaxalene is available in a block form. Rumensin CRC® is a product with a different mode of administration where a bolus is placed into the stomach that slowly releases monensin over a period of 120 days and uses the principals previously discussed. On highly susceptible pastures, this product has reduced the bloat incidence by 80%. The slow-release monensin capsule (Rumensin CRC®) is licensed for bloat prevention for cattle up to 770 lbs.
Some producer experience exists using non-liscenced products like laundry detergent that are fed at low levels and serve as surfactants. Because they are not recognized as feed products, all risks of effectiveness are born by the livestock owner.
With all these anti-bloat products, it is advisable to allow a 3 - 5 day period of product usage prior to introduction to a high risk pasture.
Conclusion
Minimizing the losses from bloat and maximizing the gains from legumes can substantially increase the producer’s profit margin. The keys for implementing legume usage require maximizing grazing management principles in conjunction with bloat control products. Although major advances have been made regarding bloat control on leguminous pastures it is important to recognize that vigilant observation is the only measure which reduces the risk of losses.
Roy Lewis, DVM, 2000. Alberta Feedlot Management Guide |