Forage-related animal disorders are caused by anti-quality constituents. Anti-quality constituents are: “Chemical compounds that have negative effects on forage intake or produce negative responses in animals consuming the forage.” Some toxic compounds occur naturally. Others result from insect infestations, while some result from microbial activity. Three main groups of plants that cause animal health problems are: 1. Poisonous plants, 2. Seasonal or conditional disorders, and 3. Species related disorders.
Poisonous plants contain some toxic compound that is harmful to livestock, either chronic or acute.
Example poisonous plants:
Herbivores tend to select nutritionally superior diets and have some ability to avoid toxins. However, they are unable to consistently avoid harmful plants, so managers must be diligent to remove harmful plants. In addition, more problems occur under conditions of overgrazing, since animals are less able to avoid harmful plants.
Occur only under certain environmental conditions, at certain plant growth stages, or susceptible animal stages.
" ... metabolic disorder characterized by low blood serum magnesium levels."
Mg concentration in forage is < 0.20% DM
Strategies for avoiding:
Treatment: Ca-Mg-gluconate solution injection
“Legume frothy bloat occurs when a stable foam forms at the surface of the floating raft of actively digesting forage in the rumen and blocks access to the esophagus, causing gases to accumulate.”
Management to reduce:
grass-legume mixtures
bloat-safe legumes (trefoils, sainfoin)
provide hay or other feed
use “bloat-guard” blocks
Treatment: vegetable oil or other antifoaming into rumen with 0.75-in. diameter hose.
“… toxicity occurs when ruminants ingest nitrate in excess of the ability of rumen microbes to convert the nitrite intermediate to ammonia.”
nitrate is common form of N absorbed
nitrate intermediate transforms hemoglobin into methemoglobin, restricting oxygen transport
forages < 0.44% DM nitrate are safe
nitrate poisoning blood is “chocolate brown”
problems usually with grasses due to over-fertilization
drought stressed sorghums commonly high in nitrate
Treatment: remove animals to another forage source, feed energy supplement, intravenous methylene blue.
“… also referred to as hydrocyanic acid poisoning or cyanide poisoning, occurs when consuming cyanogenic glycosides.”
occurs in sorghums < 18” or plants recovering from frost or drought stress
epidermal cells contain cyanogenic glucoside
mastication mixes enzymes and dhurrin leaving aglycone from which HCN is released
cyanide is absorbed through rumen wall
symptoms include rapid, then labored slow breathing, muscle spasms, dilated pupils
death occurs in 15 minutes à 2 hours from asphyxiation (inhibits cytochrome oxidase); blood color is “cherry red”
Prevention: split N applications, make hay or silage, delay grazing for 2 weeks following frost
“… naturally occurring plant phenolic compounds that mimic estrogen hormones in animals.”
phytoestrogens cause infertility (formononetin, biochanin A, and genistein)
more common in sheep than cattle
subterranean clover may have up to 5% DM
low phytoestrogen cultivars developed
red clover, sub, white, and berseem clover contain phytoestrogens
"… primary photosensitization occurs when compounds in the plant move directly to the skin and cause the reaction (sunburned, reddened, or blistered)."
occurs in cattle, sheep, horses, and other livestock
secondary photosensitization occurs when liver damage prevents normal metabolism (facial eczema caused by Pithomyces chartarum)
Oregon Veterinarian Information System (OVIS)
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