Monday, January 16, 2006

Tetany animal health issue and soil, hay links

Tetany is a complex disease in that no specific condition triggers it in all cases. Gauge tetany risk using soil and tissue analysis when growing or feeding hay comprised solely of cool-season grasses. A grass-legume mix does not have this risk.

Tetany is a disease affecting ruminants and is associated with feeding or grazing bluegrass, bromegrass, fescue, orchardgrass, ryegrass, timothy and wheatgrass. It is caused by low blood levels of calcium and/or magnesium. Classic risk conditions occur when the forage grass is growing quickly in the spring and nitrogen levels are high. Less well known is that tetany can be a problem when hay is grown on soils with excessive soil potassium. Manure and potassium hydroxide cleansers are two potential sources. Lactating animals are more susceptible to tetany, thus dairies are particularly alert to the concern and tend to avoid growing or feeding grass hay exclusively. Forage guides may not mention it as a concern. A forage tissue ratio of K/(Ca+Mg) of more than 2.2 indicates a high risk of tetany and the need to supplement feed with magnesium (Mg) (see also). If an animal goes down and tetany is suspected, a veterinarian should be contacted for immediate treatment. Often an animal will recover if it can be given an injection of magnesium sulfate (Epsom salts) early on.

Preventative Mg feed supplement and the ready supply of alfalfa tends to keep the incidence of tetany to a minimum. My thought is that tetany is additionally controlled by the close knit nature of farm communities. Caring neighbors and long memories tend to interact sufficiently that tetany symptoms don't take more than an animal or two, usually the weakest anyway, before it is figured out. Perhaps this explains why analytical laboratories in my region are generally unaware of tetany or the role of soil and tissue nutrient levels. My opinion is that cooperative extension publications in the Pacific Northwest can do better in this area. Tips for preventing animal loss due to tetany should be included in the fertility guides published to help folk interpret forage test results.

See also:
Spring Mineral Considerations by Jeff Heldt (link added 03MAR06)
Controlling Grass Tetany in Livestock, by Cooperative Extension, New Mexico State University, available in pdf format

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back40 said...

In the managed grazing community Grass Tetany by the godfather of grazing, Andre Voisin, is discussed or at least mentioned several times a year on the lists and in the magazines (such as The Stockman Grass Farmer).

Confinement dairies feed a total mixed ration that has all sorts of minerals in it, often in consultation with a private advisor. Any more it seems that it is commercial consultants rather than extension agents that are trusted and relied on for advice. The bigger the operation the more this is so.

But even the grass dairies most often feed supplements since it very hard to get everything from the pasture. One school of thought says that it is far cheaper to feed minerals to your livestock than it is to your pasture. Pasture is an indirect route.

What I wonder is how does the whole system work? Does the sum of benefits for the pasture and the animals from careful attention to soil minerals exceed the simple benefit of feeding minerals just to the animals?

Philip Small said...

IANAGHG, but if I was growing grass hay, I would be sorely tempted to cut a lot higher (3-4")than I see folks doing normally (1"). This would increase plant reserves and encourage root growth. (kudos to Steve Fransen, WSU-Pullman for pushing this) It seems reasonable that this approach would increase nutrient value and reduce reliance on mineral feed supplements.

Tissue analysis has gotten more affordable. With near infrared reflectance (NIR) spectroscopy, labs can provide vast info (incl Ca, Mg, K) for $12-$16/sample, $26/sample if you want to add more reliable wet chemistry on the minerals. At those prices, more folks are going to be able to afford to do some in-house on-farm research. Set up some test plots, compare different treatments.

The downside of cutting at 3-4" is the cutting bar has to be sharper than for 1" or some of the hay gets laid down instead of cut. This plays havoc with quality and market value on the next cutting.