Farming Magazine - June, 2012

COLUMNS

Beef: Grazing Alfalfa

By Dr. John Comerford

Alfalfa can be an effective pasture forage for beef cattle. Experiments here at Penn State (Comerford et al, 2005) have shown alfalfa/grass combinations may be the most cost-effective midsummer forage alternative in this region because they are perennial plants that have a deep root system and allow growth during drier periods. Less fertilizer cost for a legume and lower costs for seed and equipment costs compared to annual grasses means lower overall costs. Experiences in Argentina showed alfalfa was an important, and in some cases the only, source of pasture forage for cattle. There are certain precautions to take to prevent bloat when grazing alfalfa and alfalfa/grass combinations.

Bloat is caused by the accumulation of gas in the rumen and reticulum of cattle. Legumes are the primary source of pasture bloat, but other plants can also be involved. The gases are primarily methane and carbon dioxide, and they accumulate quickly when eating highly digestible legumes such as alfalfa and clover. The speed of the gas production does not allow the animal to release them by eructation (belching), and they accumulate to the point the animal cannot breathe. Frothy bloat may also occur when froth concentrates in the rumen, causing pressure that also strangles the animal. Suffocation can cause death in as little as one hour after grazing these plants, but there is generally a lag time of 24 to 48 hours before the bloat occurs (Lemenager et al, 2010).

Prevention of bloat in grazing cattle

There are a number of preventative measures that can be taken to prevent bloat in cattle grazing alfalfa, but it should be clear that there are animals more prone to develop bloat, and these cattle may develop the problem in spite of preventative measures. The following are suggestions for preventing bloat.

  • Use grass hay to fill the rumen before turning cattle out on alfalfa pastures. This allows the intake of the forage to be slowed, and the rumen microbes have a chance to adjust to the new form of feed.
  • Immature alfalfa is more dangerous than mature plants, so use other pastures early in the grazing season. This is especially important at spring turnout because the rumen microbes can get adjusted to fresh forage before dealing with a legume. Alfalfa in full bloom is more desirable. This may imply planning to harvest the alfalfa as hay early in the growing season.
  • Turn out the first time in the afternoon on a dry day and continue partial days of grazing over a week to allow the animals to adapt. Cool, wet weather and dew early in the day can contribute to bloat.
  • Grain feeding (up to .5 percent of body weight) just before turnout may help prevent bloat.
  • Partition pastures so that cattle are forced to eat the entire plant at turnout in a short grazing period. This provides more fiber in the diet instead of allowing them to only eat the top, more succulent, leafy part of the plant.
  • Provide a mineral supplement with high levels of salt. The addition of Rumensin to the mineral supplement may also be helpful.
  • Bloat preventative compounds such as poloxalene (marketed as Bloat Guard blocks) can be effective, but they are predicated on the animal actually eating it. Training the cattle to eat the block before introducing the alfalfa pasture can be helpful.
  • Cutting and windrowing alfalfa for 24 to 48 hours before allowing access by cattle can greatly reduce the incidence of bloat (Smith, 2000).
  • Remove cattle from alfalfa pastures that have been frosted.
  • All preventive measures can fail at some time, so observation and quick action by managers is necessary to prevent cattle losses.

What to do if cattle bloat

As shown above, cattle can die quickly with severe bloat, so do not delay action if bloat occurs. If cattle are still mobile, make them walk as much as possible to induce belching. A stomach tube can be inserted by mouth (with extreme care taken to be sure the tube is in the rumen and not the lungs) as an outlet for the gas. For this a garden hose with the metal end removed can be used. Mineral or vegetable oil can be added through the hose or tube (10 to 12 ounces per 1,000 pounds of body weight; Lemenager et al, 2010) to release the froth accumulation. In severe cases when the animal is threatened by suffocation a trocar is the last resort. This is a tube with a sharp end that is literally punched into the rumen through the skin to release the pressure. This procedure can result in bleeding and infection of the skin and peritonitis of the stomach if proper antibiotic treatment is not provided. Consult your veterinarian about the proper treatment.

Grazing alfalfa is not without caution, but it is also functional forage that can effectively fit into many grazing programs.

Dr. John Comerford is associate professor of dairy and animal science at the Pennsylvania State University.