Animal Health Problems: Problems Caused by Specific Forages
Excerpt from Publication 19, Pasture Production, Order this publication Table of Contents
Reed CanarygrassThe old varieties of reed canarygrass are known for being unpalatable and tough. Animals grazing the old varieties do not gain as well, produce as much milk, or appear as thrifty as would be expected based on the apparent feed quality. The cause is high levels of plant alkaloids. Alkaloids are bitter-tasting substances that are generally irritating to the gastrointestinal tract. New varieties of reed canarygrass have reduced levels of alkaloids. Feed quality, grass palatability and animal performance are excellent when these new varieties are pastured in the vegetative plant growth stage. Tall FescueA fungal endophyte in tall fescue is thought to be responsible for causing 3 animal disorders: fescue foot, bovine fat necrosis and fescue toxicity. Their occurrence is determined by the percentage of infected tall fescue plants in the pasture, the length of time the animals spend grazing infected tall fescue, the weather, and pasture fertility management. Fescue footFescue foot can occur when animals graze tall fescue in cool weather. The symptoms include a rough hair coat, loss of weight, fever, quickened respiration rate, tenderness of the legs and, in advanced cases, loss of hooves, ears and the tail. Bovine fat necrosisBovine fat necrosis is characterized by an accumulation of hard masses of fat along the alimentary tract. This condition results in digestive upsets and problems in giving birth. Pregnant horses grazing infected tall fescue do not prepare for foaling and may give birth to a dead foal. Remove pregnant mares from infected fields 30 days prior to the expected foaling date. Bovine fat necrosis is associated with fertilizing infected tall fescue pastures with high rates of nitrogen fertilizer or with broiler litter. Fescue toxicityFescue toxicity occurs during hot weather. The symptoms are poor gains, lowered conception rates, intolerance to heat, failure to shed the winter hair coat, fever, excessive salivation, and nervousness. PreventionThe only known means of spread of the endophyte is by infected seed. It is possible to prevent these associated animal disorders from occurring by using certified endophyte-free seed or by just using a small percentage of tall fescue in the pasture. Sorghum-Sudan Hybrids, Sudan Grass and SorghumsBesides prussic poisoning (discussed above) these plants can cause urinary tract infections in horses. The symptoms are similar to colic but include bloody urine. The condition can be fatal and it is recommended that horses not be allowed to graze these plants. BrassicasBrassicas are useful for extending the pasture season into the late fall. However, they do have problems. In addition to causing bloat and nitrate poisoning, they also cause forage rape poisoning, anaemia, goitre, rape scald and rape blindeness. Forage Rape PoisoningForage rape poisoning can occur if animals graze stunted, purple-coloured rape plants. This type of plant is produced when rape growing in wet conditions, or on soils deficient in phosphate, are frosted. Animals affected take shallow, rapid breaths and suffer from digestive disturbances. Death may follow. When the affected animals recover they often remain unthrifty. AnaemiaBrassicas contain a haemolytic factor that may cause grazing animals to suffer from anaemia. Cattle are more susceptible to this disorder than sheep. Anaemia only develops when the livestock are grazing brassicas for at least one week and it usually takes 3 weeks to occur. In extreme cases, haemoglobin appears in the urine, giving it a red colour. The amount of the haemolytic factor in brassicas increases as seeding dates are delayed in the summer and with plant maturity. GoitreAll brassica crops contain goitregenic substances. The goitregen affects the uptake of iodine by the thyroid gland and goitre develops. Goitre can occur in all animals grazing brassicas, but is more of a concern with sheep. Do not use brassica pastures during the mating season or for eves late in their pregnancy. Lambs may be born dead or deformed. Rape ScaldWhite-faced sheep grazing brassicas in August and September may suffer from "rape scald" Their lightcoloured skin becomes susceptible to sunburning and their heads may swell. Forage rape can taint the flavour of milk and meat if it is the main source of feed. Rape BlindnessRape "blindness" is the sudden appearance of blindness in cattle and sheep grazing rape. Complete recovery of sight normally occurs a few weeks after the livestock have had a change of diet. Limit the feeding of brassicas.
Related Links... on forages and pastures, visit Forages
and Pastures (OMAFRA)
For more information: Toll Free: 1-877-424-1300 Local: (519) 826-4047 E-mail: ag.info.omafra@ontario.ca
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