Thursday, March 9, 2006
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Nutritional Considerations for Spring Forages
by Justin Sexten, Extension Specialist, Animal Systems/Beef
Warmer temperatures and rain suggest the spring grazing season is near. Livestock producers need to consider two common forage-related nutritional disorders, grass tetany and pasture bloat.
Grass tetany or “staggers” is a result of low blood magnesium and is generally observed in older, high-milk producing animals grazing N-fertilized cereal or grass pastures. These animals are susceptible due to the increased magnesium requirement of lactation combined with the older animals’ inability to mobilize bone magnesium. Legumes contain increased levels of magnesium compared to pure grass or cereal grain pastures. So frost seeding legumes into grass pastures not only aids in preventing grass tetany next year but will also lower nitrogen fertilization needs.
Beyond adding legumes to pastures, magnesium supplementation is the best method of preventing grass tetany in susceptible animals. Magnesium is generally considered unpalatable, so it should be added to a mineral or grain supplement to encourage intake. Supplementation will only be effective if animals consume adequate levels of magnesium, so make sure intake matches product recommendations.
Adding legumes to pastures assists in preventing grass tetany but may add another management challenge, pasture bloat. Bloat is a result of animals’ inability to belch excess rumen gas due to ruminal foam formation. Lush legume pastures are generally associated with bloat due to favorable foam formation properties such as high soluble protein and moisture levels combined with low fiber concentrations. Fear of bloat should not prevent producers from incorporating legumes into pastures since management can prevent pasture bloat.
Pastures should contain no more than 40 percent legumes; this is the optimum level for minimizing bloat while maximizing nitrogen fixation. Avoid turning hungry animals into legume-containing pastures by providing hay prior to pasture turn out and rotating animals through pastures quickly leaving a longer residual pasture height. Forages covered with dew can increase the risk of bloat so move animals to new pastures midday rather than early morning. If bloat is still a problem consider using a poloxalene containing supplement or “block” to prevent foam formation.
Justin Sexten, 618-242-9310, firstname.lastname@example.org
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