Alfalfa hay fields are a valuable pasture resource for conditioning cattle and sheep in the fall and early winter. A major concern is to avoid BLOAT (plus reducing potential stand damage).
There are no hard-and-fast rules for an exact freezing temperature that makes alfalfa “safe” to graze. However, there are some crop and livestock growth principles to consider before fall grazing of alfalfa:
1. Pasture bloat is primarily a function of rapidly-degrading soluble proteins – alfalfa, as well as other legumes and crops at a lush growing stage have high levels of these soluble proteins. Hard frost ruptures alfalfa cell walls, so a high level of soluble proteins are immediately present before consumption and mastication by an animal.
2. Alfalfa hay rarely causes bloat – at 12 to 15% moisture, intake and feed passage rate are slower which reduce the formation of frothy gas in the rumen (compared to 80% moisture of lush standing forage). Wilted forage (windrowed hay) is safer to graze than standing alfalfa.
3. Pre-conditioning for all livestock seems to be a key ingredient – coming off dry grass into lush alfalfa regrowth can set you up for disaster. This is primarily due to the population of the rumen microbes which take some time to adapt to higher-quality feed.
4. Pasture bloat “storms” are most pronounced in the spring or fall regrowth, when frosts are occurring, but rare cases can occur even on mature alfalfa in mid-summer.
5. Alfalfa generally becomes “safer” to graze in the fall after several consecutive frosts in the 20’s that causes visible plant damage and drydown. When Tye MacDonald was doing his alfalfa grazing trial, we purposely grazed well-irrigated alfalfa regrowth during the week in mid-September when first frost was predicted by the weather service. (The weather was similar to right now- warm afternoons/cool nights). We had few minor bloat cases until the morning following our first frost - in this case, it was about 28 degrees for a couple of mornings in a row and was accompanied by many incidences of bloat for several days. Alfalfa that is more mature or drought-dormant in the fall appear to be safer than 6 to 8 inch, lush regrowth, however this is not 100% because individual animals may selectively graze leaves or in lush areas.
6. Our best recommendations are to avoid grazing until there is significant alfalfa frost damage. Slow adaptation to the pasture is needed – turn animals out “full” for several afternoons and observe them. Livestock access to dry pivot corners, dry pastures, crop stubble or hay is good so animals can balance their intake of dry and wet forage. Also, providing a bloat block is advisable (products such as Silent Herder, Rumensin and others are often cited as reducing bloat).
7. Last, monitor livestock daily and if any suspected bloats occur, treat them and remove the rest of the herd immediately before trying to confirm the cause of the problem.
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