By Peggy Joseph-Potter RN, BSN, MHA
Spring rains bring burgeoning foliage and for most beef producers the ever important lush green grass. While this welcome addition may delight many a farmer, it is not without a sinister side. Grass tetany is a feed related metabolic disorder which can prove harmful and at times lethal for cattle.
Grass tetany, “grass staggers,” wheat pasture poisoning, or hypomagnesaemia, can be a problem in the spring when immature grass is prolific. This disorder is more prevalent in older lactating cows as it is theorized they are less able to mobilize their magnesium storage from their bones than their more capable counterparts. High nitrogen fertilization reduces magnesium availability, especially on soils high in potassium or aluminum. Grass tetany occurs most frequently in the spring; often it follows a period of cooler temperatures such as those between 45 and 60°F, causing the grass to grow rapidly. This condition is also seen in the fall with new growth of cool season grass or wheat pastures.
The greatest risk for grass tetany is when pastures soils are low in available magnesium (Mg), high in available potassium and high in nitrogen. Pastures where a significant amount of manure has been applied often have this mineral imbalance and are considered more vulnerable. Soil testing can aide in the analysis of such pastures to determine what nutrients need to be added to prevent the onset of this metabolic disorder. While the name denotes grass and wheat as the culprits, grass tetany can occur from any sort of foliage including orchard grass, perennial ryegrass, timothy, tall fescue, crested wheat grass, brome grass, Kentucky bluegrass, annual ryegrass and small grain (wheat, oats, barley, triticale and rye) pastures. It can also occur when livestock are wintered on low Mg grass hay or corn stock. Other factors which have been associated with this disease include low levels of Mg and high protein and potassium levels in the forage.
Common factors present with grass tetany include the following:
Animals are usually grazing grass dominant pasture or lush cereal crops, often without any hay supplementation.
Cold and wet windy weather with little or no shelter, resulting in short periods of fasting.
Animals are either fat or losing condition or very thin.
Animals recently moved to a different paddock.
Heavy use of nitrogen and/or potash fertilizer on pasture.
Cows in peak lactation are most commonly affected, but dry cows and, under certain conditions, beef steers, may also suffer.
Symptoms: In the early stages, animals are observed to walk very stiffly, with lost flexibility of their hind legs. It is this swaying gait which gives the impression that the animal is staggering, hence the English name “grass staggers.” Animals may have an over-alert appearance, being excitable and aggressive. The animal has no appetite and looks mournful. Its eyes are glazed and bulging to a certain extent. In the latent stages the animals progresses to convulsions, high fever and if left untreated will be found down with an unlikely survival.
Physical symptoms include:
Muscles: Stiff with contraction of the tail
Muzzle: Mouth close and difficulty to open; grinding of the teeth; frothing at the mouth
Eyes: Wild, blood shot, frequently rolling
Head: Thrown back
Pulse: Feeble and rapid
Udder: Normal with no extensive softness
Temperature: Normal or high (104)
Treatment: When symptoms are observed, prompt treatment by a veterinarian is required. The intravenous injection of a combined calcium and magnesium solution (350ml) under the skin in the area behind the shoulder and over the ribs is most effective. Massaging the area well after injecting the solution will spread the fluid and aid its rapid absorption into the blood stream. Treated animals should be given adequate shelter and identified so that a response to treatment can be monitored. In some situation, repeat treatment maybe indicated.
Cattle affected by grass tetany often relapse and die or become ‘downers’ and eventually have to be destroyed. Time is of paramount importance to success of treatment. Prompt identification and initiation of medication and stress reduction related to weather improve treatment efficacy. Often affected animals do not eat – this can be a very serious complication, especially in pregnant cattle which often succumb to pregnancy toxemia and die.
Prevention: To prevent grass tetany cattle should be feed a high Mg supplement or free-choice minerals. Magnesium may be added to grain, protein or liquid supplements. Magnesium sulfate is the most palatable source and since magnesium stored in the body is not rapidly available it must be supplied at least every second day during the “danger period.”
Grass tetany blocks provide magnesium as a palatable ‘lick’. A major disadvantage of this method is that all the animals may not consume sufficient magnesium. Follow the manufacturer’s instructions concerning the number of cows per block. When buying blocks, be sure that they are recommended for the prevention of grass tetany.
Feed mineral supplements that contain magnesium. Commercial mineral mixtures containing 10-15% magnesium are available for feeding during periods of increased grass tetany probability. Cattle need to consume 6-12 oz/head/day of this mineral.
Feed mineral mixtures with Iodine and Cobalt 30 percent bone meal or dicalcium phosphate, 30 percent Magnesium Oxide, and 10 percent dried Molasses. This mixture provides about 18 percent Magnesium.
Epsom salts or magnesium chloride may be added to the water supply. The salts can also be added at the rate of 60g per cow per day (60 g is about two level tablespoons). The dose must be split and added to the water on two occasions during the day. The normal water flow should be maintained. The capacity of the trough should be at least nine quarts per cow so that the salts are sufficiently diluted. Cattle will scour if they get more than 140 g of Epsom salts per day. Also, because cattle don’t like the taste, the Epsom salts need to be added gradually over 2-3 weeks. There are several disadvantages in using this method. Epsom salts are unpalatable and not readily accepted by stock. In winter, water consumption is variable due to the high moisture content of the feed and as a result insufficient salts may be ingested.
Drenching stock with magnesium oxide or Epsom salts mixed in water is an effective but time consuming, method. The daily rate is 60g/cow mixed in 100 ml water. Epsom salts may be mixed with bloat treatments but the volume of water will need to be increased if such a mixture is used. The magnesium oxide drench mixture must be constantly shaken to prevent it settling out.
Magnesium oxide (Magnesia) may be added to feed fed in the bail at the rate of 45-50 g per cow per day but there are indications that levels greater than 30g per cow per day may predispose the cows to Salmonella.
Remove animals from pasture or limit grazing during periods of rapid growth. Allow access to hay or dry pasture. Also, producers may want to limit grazing of the temporary winter pastures when moving cattle directly from poor quality frosted grass pastures. A rapid change in feed can cause digestive upsets and nutritional stress.
Fertilization suggestions: Fertilizers rich in potassium and nitrogen reduce the availability of magnesium from the pasture, and increase the risk of grass tetany. So avoid grazing these pastures soon after fertilizer application. On soils that need liming, use dolomitic limestone. If lime is not needed, magnesium can be included in mixed fertilizers. Do not exceed the recommended level of applications for nitrogen and potassium on winter pastures for grazing consequently, these fertilizer elements should not be applied in excess on temporary winter pastures. Follow recommendations based on soil test results.
Grass Tetany, Grass Stagger. (2011, October 6). Retrieved March 15, 2012, from Department of Primary Industries, Parks, Water, Environment.
Allison, C. (n.d.). Controlling Grass Tetany in Livestock. Retrieved March 15, 2012, from Cooperative Services, College Ag and Home Ecomonics, New Mexico Universtity.
Haynes, N. B. (1978). Keeping Livestock Healthly. North Adams, MA: Storey Publishing, L.L.C.
Thomas, H. S. (1998). Storey’s Guide to Raising Beef Cattle. Storey Publishing.
Y.C.Newman, M. (2010, October). Grass Tetany. Retrieved March 15, 2012, from Agonomy Department,Florida Cooperative Extension Service, Institute of Food and Ag Science: ifas.ufl.edu
Peggy and her husband, Bob Potter, own and operate PJ Ranch LLC in Winton, California, where she serves as the Vice President of Animal Health. They have been Miniature Hereford owners and active participants in the MHBA since 2002. She is also employed as a critical care nurse for a local medical center.