Grazing Alfalfa and Prevention of Bloat

 

Alfalfa is one of the most nutritious forages available and can support beef production levels comparable to feedlot systems. Grazing pure alfalfa stands can significantly increase net farm income—yields of up to 1,371 lbs of beef per acre have been reported. Even with some forage waste, alfalfa out-produces grass and improves soil fertility through nitrogen fixation. However, its use for grazing is limited due to the risk of pasture bloat.

 

Signs of Bloat

  • Distension on the left side
  • Frequent urination and defecation
  • Kicking at the flank
 

Why Bloat Occurs

Alfalfa digests rapidly in the rumen (the largest of 4 stomachs in a ruminant animal) - 5–10 times faster than grasses—allowing cattle to consume more forage but increasing gas production. This rapid digestion by bacteria and enzymes reduces plant particles quickly and moves it to the digestive tract. Under certain conditions, foam can form within the rumen, trapping gases such as carbon dioxide and methane. This prevents normal eructation (belching), inhibiting the release of these fermentation gases and potentially leading to digestive complications. Severe cases can lead to respiratory failure and death.

 

Risk Factors

  • Highest at vegetative to early bloom stages
  • Decreases after 15–20% bloom
  • Soluble protein levels are higher early in the day
  • Frost does not make alfalfa bloat-safe; freezing ruptures cells and increases soluble protein release. Alfalfa is generally safe two weeks after a killing frost.
 

Key Factors Affecting Bloat Potential

  • Soluble Protein Content and Type
  • Presence of Condensed Tannins
    • Tannins reduce bloat risk by precipitating soluble proteins.
    • Non-bloating legumes include birdsfoot trefoil and vetch.
  • Rate of Soluble Protein Release
    • Example: Cicer milkvetch is non-bloating despite lacking tannins due to slow protein release.
 

Management Strategies for Grazing Alfalfa: Bloat Prevention

  • Delay grazing until alfalfa has wilted or dried.
  • Move cattle in the afternoon (2–5 p.m.), not in the morning.
  • Avoid turnout two days after rain during hot weather—alfalfa grows rapidly and bloat risk is high.
  • Maintain “escape” pastures to remove cattle if conditions become unfavorable.
  • Monitor grazing behavior—ensure cattle are mixing alfalfa with grass.
  • Hay paddocks in advance if necessary to manage forage availability.
  • Avoid continuous grazing of a single paddock; after 2–3 weeks, alfalfa regrowth increases bloat risk.
  • Avoid interrupted grazing; maintain continuous intake.
  • Use bloat-reducing supplements.
  • Pre-feed cattle with hay before turnout to prevent overconsumption.
  • Introduce cattle gradually and maintain continuous grazing once started.
  • Monitor during environmental stress (storms, heat, flies) to prevent “bloat storms.”

Observation Tip: Major grazing bouts occur after sunrise and early evening; bloat typically appears 1–1.5 hours after grazing.

Agronomic Approaches

  • Co-cropping alfalfa with bloat-safe legumes such as sainfoin or birdsfoot trefoil.
  • Wilting alfalfa for 24–48 hours before grazing to lower bloat potential.

Feed and Water Additives

  • CRC bolus (Rumensin): Added to feed supplements to help prevent bloat.
  • Alfasure: A liquid additive for controlled water sources; effective for prevention.
  • Emergency Treatments: Alfasure or Dioctol can be administered directly into the rumen to relieve bloat.

Alfalfa Is Not Bloat-Safe After a Killing Frost

As the grazing season ends, many producers consider grazing frost-killed alfalfa. While frost rarely causes nitrate toxicity in alfalfa, testing is recommended, especially where soil nitrogen is high. Nitrate issues are more common in annual species and sorghums, which may also accumulate prussic acid under stress. The primary concern with alfalfa after frost is increased bloat risk.

 

Alfalfa and Frost

  • Alfalfa remains a bloat risk while green and succulent, even after frost.
  • First frost ruptures plant cells, increasing K+, Ca²+, Mg²+, and small fragments—raising bloat risk.
  • Bloat risk declines only after substantial drying (typically one week post-frost).
  • Field-cured alfalfa for baling poses no bloat concern.