Forage Related Disorders

As spring approaches and grass begins to grow, grazing livestock may experience a forage-related problem known as grass tetany, grass staggers, lactation tetany, or hypomagnesemia. Grass tetany is a metabolic disorder caused by reduced magnesium (Mg) levels in the animal’s blood. In cattle, it generally affects older, lactating cows but can also be seen in dry cows, young cows, and in rare cases, growing calves. Symptoms often observed include nervousness, lack of coordination, muscular spasms, staggering, convulsions, coma, milk yield decrease, and death.

by Dr. Michelle Arnold, Extension Ruminant Veterinarian - Brassicas (including turnips, rape, kale, and swedes) are highly productive, digestible forbs that contain relatively high levels of crude protein. Animals will readily consume the tops and will also grub the root bulbs out of the ground. Dry matter yield depends upon soil type, fertility, time of seeding, and precipitation.

Prussic Acid (Cyanide) Poisoning

As temperatures continue to decrease, it is important to know and understand how various species of forages react to frosts and freezes in order to best utilize these forages and to avoid possible health problems. Freezing changes the metabolism and composition of plants. Depending on plant species, this can create possible forage-related animal disorders or the need to alter grazing management practices. 

A frost or freeze can greatly affect how one uses alfalfa later in the year. Although frost-damaged alfalfa is not toxic, one should be cautious when grazing alfalfa after a hard freeze (less than 25˚F) as the threat of bloat increases after the freeze. Once wilting starts risk of bloat is reduced. Waiting a few days after a freeze is a good practice to decrease this risk when grazing alfalfa. If forage is needed and you plan to cut alfalfa for hay late in the year, cut after the first hard freeze or in early to mid-November.

Cyanide poisoning, more commonly referred to as prussic acid poisoning, can have a very abrupt and deadly effect on ruminant livestock grazing forages and requires careful management as frosts and freezes begin in the area. Plants, such as sorghum, sudangrass, sorghum-sudan hybrids, Johnsongrass, wild cherry, and others, contain compounds that produce free cyanide when these plants are damaged by frost or drought conditions. Grazing these plants when they are producing young shoots (less than 18 to 24 inches tall) also increases the risk.

Nitrate toxicity may be a problem for farmers grazing corn or feeding green-chop this fall. There are many factors to consider when deciding if livestock are at risk of nitrate toxicity. Drought conditions and high levels of nitrogen in the soil can cause prime conditions for high nitrates in plants. During times of drought, higher levels of nitrogen are taken up by the plants. Risk is increased if soil nitrogen levels are high. High levels of nitrates in the bloodstream and rumen reduce the ability of oxygen to be carried in the blood to tissues in the body.

Grazing forages during the summer months is a great way to reduce stored feed costs. However, there are some risks that come with grazing certain forages and weeds. It is important to be cautious this summer to reduce the risk for prussic acid poisoning, as prussic acid poisoning tends to be worse during times of drought.

The most predominant forage grass in the U.S., covering over 36 million acres, happens to be tall fescue, a cool-season perennial grass. It is extremely prevalent in areas of the southeastern United States because it possesses desirable characteristics that include tolerance to drought, flooding, heavy grazing pressure, and a long growing season. Kentucky-31 Tall fescue contains a fungal endophyte that grows in the plant and is responsible for many of tall fescue’s desirable survival attributes.

by Michelle Arnold, DVM - In the Southeastern US, a severe type of pneumonia can result from ingestion of the leaves and seeds of perilla mint (Perilla frutescens). This common weed is also known as purple mint, wild coleus, mint weed, or beefsteak plant. Perilla mint thrives in late summer, when pastures are frequently dry and dormant. The weed prefers shaded areas along creeks, the edges of the woods and in fence rows. Once it becomes established, perilla mint produces many seeds and large colonies can develop in succeeding years. 

Dr. Jeff Lehmkuhler, Extension Beef Specialist - Pastures were slow to green-up with the cool weather this spring. However, the past few days of warm weather has really made the grass pop. I noticed today, April 18, that some of the timothy and bluegrass was beginning to flower. Now is a good time to be investigating pasture stands for legume content.