September rain brings pasture regrowth, abundance of annual bromes
By Casey Matney
Rangeland Extension Specialist
Thanks to September rainfall, our cool-season pasture grasses are having a lot of green growth this October. This growth is giving an added carbohydrate boost to our perennial grasses as they prepare to go dormant for the winter.
Such growth can also provide added forage for fall/winter grazing, but is there a downside to having so much fall regrowth? Two potential downsides exist: 1) grass tetany, and 2) an abundance of cheatgrass and Japanese brome.
Grass tetany occurs when cattle feed on young leaves of rapidly growing grasses. Grass tetany is also called grass staggers, hypomagnesemia, winter tetany, and wheat pasture poisoning. Caution periods are in spring when perennial grasses begin growth or in the fall/winter when grasses are initiating regrowth. The germination and new growth of winter annual grasses are also a factor in the fall/winter caution period. Consumption of grasses having low fiber and high moisture content with low magnesium levels results in cattle having diminished magnesium levels in the blood. Magnesium is important in many enzymatic reactions in the body. Stress, extreme weather, and forages high in nitrogen/crude protein and potassium can exacerbate the magnesium deficiency in the forage. Pastures fertilized with ammonia or having soils with high nitrogen and potassium levels can also increase the risk of grass tetany in spring and fall/winter. Lactating cows have a greater risk for grass tetany.
Forages having more than 0.2 percent magnesium, on a dry matter basis, are generally considered safe. Acute cases of grass tetany can result in death within one hour of the onset of symptoms. Symptoms may develop within a few hours. Animals suffering from acute poisoning may show symptoms prior to death including excitability, aggressiveness, abnormal walk, vocalization, convulsions, and frothing at the mouth. Chronic or subacute symptoms of grass tetany that can develop over a period of days include staggering and abnormal walk, excessive blinking, lack of appetite, weight loss, and decreased milk production. Treatment of animals suffering from grass tetany consists primarily of an injection of solution containing magnesium, calcium, and dextrose. Contact a veterinarian if you suspect your cattle are showing signs of grass tetany.
Grass tetany is preventable. Providing cattle with a magnesium supplement can prevent and reduce the risk of grass tetany. Examples of magnesium supplements include licks, capsules, and a powder that can be added to forage dry or as a liquid mix. Supplementation of magnesium should occur before releasing animals into pastures with a suspected risk for grass tetany. Cattle will need to remain supplemented with magnesium as long as they are consuming deficient forage.
Abundance of cheatgrass and Japanese brome
You might be noticing a surprising carpet of young green grass shoots 2 to 4 inches tall growing between the larger bunchgrasses and shrubs this fall. This abundance of young grass plants comprises mostly cheatgrass and Japanese brome. Cheatgrass and Japanese brome were prolific this summer, but now a multitude of seeds from those parent plants are emerging. These newly emerging plants stand a high chance of surviving the winter.
The one good aspect of this mass of new growth is that it can potentially provide forage for cattle through the spring. If your cattle are grazing cheatgrass this fall or spring, beware of grass tetany. However, if these new stands of cheatgrass are not sufficiently grazed or controlled by early this next spring, we could be looking at record numbers of cheatgrass that could be competing for water, nutrients, and space with desirable perennial grasses. To make the situation worse, this carpet of cheatgrass could expand in 2014 as well as greatly increase the risk and severity of wildfire, which is all the more reason to plan on controlling the cheatgrass as we enter the 2014 growing season.
If you can, make what grazing-use you can of cheatgrass and Japanese brome prior to the development of seed heads, which typically occurs during late April and early May. In addition, try to include chemical and mechanical methods to control these annual bromes. For information on how to control annual bromes and understand the wildfire risk they pose, visit http://www.ext.colostate.edu/pubs/natres/06310.html.