Alfalfa conditions may result in bloat hazard when grazing


 By Sharla Sackman
Prairie County Extension Agent

Recently, MSU  Extension Specialists Dennis Cash and Rachel Endecott sent out a news release on grazing alfalfa in 2010. Following are some highlights from that article.

After Labor Day weekend, many Montana ranchers begin sizing up their hay crop and pastures for fall and winter feed. Alfalfa and alfalfa-grass hay fields are widely utilized as a hay-stockpile system in Montana and the Northern Great Plains. Alfalfa aftermath in late summer and autumn is high-quality pasture for pre-conditioning calves, putting body condition on bred cows and flushing ewes. Alfalfa re-growth is a rich source of protein, energy, vitamins and minerals. However, due to the potential for pasture bloat, ranchers should always be cautious when grazing alfalfa-dominated hayfields. 
What is pasture bloat? Ruminant livestock grazing lush pastures of alfalfa, clovers, and small grains are prone to a condition called “frothy bloat.” Rapid digestion of forage containing highly-soluble proteins result in a foam which prevents rumen gases from escaping normally. Individual animals or a herd can experience severe symptoms including rapid death. The bloat hazard of alfalfa generally increases with lush, vegetative growth, during cool weather (spring or fall frosts), rain, and with high soil fertility, but can occur any time during the summer. For season-long grazing, the rumen microflora can adjust such that an animal becomes bloat-tolerant. Alfalfa-based pastures are very productive for grazing yearlings. However, rapid changes in diet quality (such as moving cows from dry grass to lush alfalfa) are risky. 
Why is alfalfa grazing in the fall risky? It appears that many of our livestock feeding issues in the autumn and winter are directly related to vast changes in diet quality and the environment. For example, bloat on an alfalfa pasture, nitrate toxicity of cereal hay, and many illnesses or mineral imbalances occur as a result of quick shifts in forage quality and quantity. A particularly risky time for grazing alfalfa is immediately following a frost. 
From 1998 through 2000, MSU Extension conducted grazing experiments with cattle and sheep on pure stands of alfalfa. Grazing occurred in 10 trials from late spring through late summer. Bloat incidence and severity were evaluated. Across all three years, bloat incidence was most severe in late spring and late summer, but occasional bloat “storms” occurred during mid-summer. In 1999, bloat was monitored over several days in which the weather forecast predicted a first frost. On September 3, 8, 9, and 10, the overnight minimum temperatures were 34, 36, 33 and 26 degrees. September 10th was one of the worst bloat days during the study with 80 percent of the ewes in the study bloating. 
Immediately following a “hard” freeze (defined as adequately cold to rupture cell walls), the risk for bloat increases. In general, the forage becomes safer to graze after the stems have collapsed and dried for several days after freezing. 
In 2010, many producers across the state avoided taking a second or third cutting of alfalfa hay fields due to bountiful hay supplies and low prices. Delayed first cut alfalfa, and cool, wet conditions have resulted in a large supply of lush alfalfa re-growth for fall pasture. In short, these conditions are fairly risky for alfalfa bloat this year.
How do I prevent or control bloat? Several legume species such as sainfoin, cicer milkvetch, and birdsfoot trefoil do not cause bloat, so consider these when renovating pastures. A number of products are promoted as “bloat preventative,” including specific mixes of alfalfa varieties, ionophores, and mineral mixes. However, the most studied and effective treatment is Poloxalene (Bloatguard) combined with good animal health practices such as mineral supplementation and vaccinations.
Other grazing tips include: The alfalfa should be flowering. Livestock should be fed dry roughage before turning out to graze on alfalfa pasture. The pasture should be dry, and grazing should be continuous rather than frequent corralling or movement. Paddock rotation should occur in the afternoon. Initially, animals should be monitored multiple times daily, and daily thereafter. The intake of Poloxalene should be monitored, as intake will vary among animals and days. 
In summary, the value of alfalfa pasture in the fall is very high if the risk of pasture bloat can be controlled.

Published Sept. 22, 2010

Article Type: 
Guest Opinion

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