Ergot alkaloids of increasing concern
Ergotism can occur in all animal species and its impact on production should not be underestimated.
Ergot is a fungal disease that primarily affects rye, triticale, barley and wheat, and which adversely affects the health and productivity of livestock.
The fungus in question produces the ergot responsible for the ergot alkaloid group of mycotoxins and parasitizes the seed heads of plants at the time of flowering. It is often seen in years where wet weather prevails in the spring and early summer, during the flowering stage of cereal crops or when low temperatures are present during grain fill.
Ergot infection reduces grain quantity and quality. It replaces grain kernels with poisonous alkaloid-containing ergot sclerotia - hardened bodies that are formed by the fungus.
Despite using cleaning techniques at mills, ergot alkaloids have been detected in surveys worldwide. Fungal endophytes (Neotyphodium coenophialum), which infect perennial ryegrass (Lolium perenne) and tall fescue (Festuca arundinaceous) also produce alkaloids that impair animal health and performance. Animals grazing these pastures can lose body condition, and have low conception rates and lower survival of offspring.
Additionally, body temperatures are elevated and reduced blood flow to extremities can result in death of these tissues. In mammals, ergot alkaloids affect immune and reproductive systems as well as the central and sympathetic nervous systems as some possess hallucinogenic properties.
Ergotism is one of the oldest known mycotoxicoses. Ergot alkaloids exert toxic effects in all animal species, and the most prominent toxic signs can be attributed to the interaction of ergot alkaloids with adrenergic, serotinergic and dopaminergic receptors. Recently, ergot alkaloids have gained considerable relevance due to, amongst other things, ergopeptine producing endophytes causing breeding problems in animals. The amount and pattern of alkaloids produced varies between fungal strains, the host plant and geographical region.
The term ergot alkaloid refers to a diverse group of some 40 toxins.
Toxicity in animals
Animals can be exposed to complex mixtures of ergot alkaloids in many typical production systems. This mixture results from the fact that the kinds of alkaloids present in grains and their levels can vary widely. Consequently, it is practically impossible to determine the exposure to individual toxins.
Due to the fact that animals are exposed to a multiplicity of alkaloids when consuming endophyte-infected tall fescue, a combined alkaloid effect has been suggested. In addition to vasoconstriction, other symptoms reported as typical include gangrenous changes, neurotoxic signs including convulsions, abortions and death. Moreover, reduced prolactin secretion and consequently agalactia are major adverse effects in animals.
Negative effects of ergot alkaloids have been observed in sows fed sorghum grain infected with sorghum ergot (17% C. africana ergot sclerotia) before farrowing. Symptoms included shrunken udders, lack of colostrum production, signs of oestrus and dead piglets due to starvation. Sows fed the grain after farrowing showed severe reductions in milk production due to low levels of prolactin.
Moreover, agalactia (due to the interference in the release of prolactin), feed refusal and consequent reduced weight gain are classical signs of poisoning by rye ergot (C. purpurea). Other frequently noted symptoms include strong uterotonic effects, causing stillbirths and reduced pregnancy rate.
Other studies have reported negative effects on the cardiovascular and central nervous systems due to higher blood pressure causing vasoconstriction. Defining the tolerable level of ergot in diets for weaned pigs is important to help use infected grains safely. A trial with ergot alkaloids to evaluate the performance and clinical symptoms in weaned pigs found that the maximum tolerable levels of ergot in the diet were 0.10 and 0.05% based on average daily gain and average daily feed intake, respectively, which corresponds to1.04 mg to 2.07 mg of total alkaloids per kg diet.
Trials in poultry have found that chickens fed contaminated diets (150 or 300 mg ergotamine/kg) exhibited poor feathering and developed gangrenous lesions on the toes when exposed to a continuous, temperature environment (22°C). These birds consumed less feed and water and grew poorly, and these effects were exacerbated on exposure to a higher temperature (35°C).
In birds, prolactin is involved in incubation behavior and broodiness. Ingestion of ergotamine results in reduced circulating prolactin concentrations resulting in reduced circulating concentrations of gonadotropins and thus ovarian regression. In layers, feed intake and egg production are significantly reduced when ergot sclerotia (2%), from rye or triticale are included in the diet. Other studies have found that chickens fed with diets containing 2.5 and 5.0% sclerotia exhibited respiratory difficulties, diarrhea, and death. Blackening of beaks, claws and feet, followed by necrosis of these parts were the most obvious signs.
Birds fed grains containing ergot´s sclerotia have been seen to be reluctant to move; their feet were uniformly dark, reddish purple, and they were slightly dehydrated. They also exhibited purplish-black claws, toes, shanks and beaks on several three day old chicks.
Symptoms of ergot poisoning are more pronounced when animals are kept outside under varying weather conditions.
Adult ruminants are considered less susceptible to mycotoxins, since the alkaloids are metabolized quickly. The rumen microbes may be influenced in their activity in deactivating the alkaloids by varying feed intake and passage rates through the rumen. It has been found that approximately 94% of the alkaloids ingested by cattle grazing endophyte-infected tall fescue were found in urine and the remaining 6% was in the bile. Usual symptoms of acute poisoning are lameness and gangrene due to constriction of the blood vessels and occasional convulsions. Cattle fed ergot infected sorghum had reduced ability to shed heat, which in turn reduced feed intake and growth.
Poor reproductive performance or decreased pregnancy and calving rates have also been reported. Reduced testicular development and sperm production in males fed endophyte-infected fescue seed has also been reported.
Toxic effects from cattle consuming endophyte infected fescue are manifested by one of three main pathologic conditions: fescue foot, fat necrosis, or summer syndrome.
Fescue foot occurs mostly during cooler weather (<15°C) and is characterized by rough hair coat, emaciation, limb swelling, development of necrotic tissue, and sloughing of tail and ear tips in extreme cases. Fat necrosis, or lipomatosis, results in deposition of hard, necrotic mesenteric fat around the intestinal tract, leading to impaired digestive function and sometimes death. Summer syndrome is the most prevalent and well-studied condition caused by grazing endophyte infected fescue, where cattle suffer reduced feed intake and average daily gain. Chronic ingestion of low levels of the toxins may result in overall decreases in productivity through decreased milk production, reduced weight gain, diarrhea, reduced reproductive efficiency, spontaneous abortion, and heat stress. Studies have reported that, in late pregnancy, abortions occurred 7-11 days following exposure to ryegrass pasture heavily infested with ergot.
Researchers have reported that feeding tall fescue hay containing a high level of ergovaline can reduce the performance of lactating dairy cows even with relatively cool temperatures and at a relatively high dietary ratio of concentrate to roughage. In the rumen fluid, concentrations of isovalerate, propionate and ammonia nitrogen are significantly influenced as is the amount of protein ruminally undegraded; conversely, the fermentation of neutral detergent fiber, tends to increase with the ergot supplementation at higher levels of feed intake, which might indicate a modification in the microbial population.
Lambs kept outdoors administered aqueous suspensions of milled ergot from C. purpurea (0.75 g sclerotia/kg body weight) have shown signs of dullness, inappetence, high pulse rate, diarrhea, edema of the hind legs and tail, as well as lameness.
Post-mortem findings have included inflammation and necrosis of the forestomach and intestinal mucosa. Ergovaline ingestion suppresses feed intake, reduces serum prolactin level, and reduces thermoregulatory function, which leads to increased body and decreased skin temperatures, elevated respiration rates and reduced live weight gain. Endophyte (Neotyphodium lolii)-infected perennial ryegrass causes high loss of ewes and weaned lambs and seriously disrupts breeding goals, increases lameness in sheep and cattle and elevates the incidence of pregnancy toxemia.
Ewes pastured on high endophyte-containing fescue before breeding take longer to conceive or have a reduced conception rate and experience embryonic mortality.
The effects of ergot alkaloids in animals are diverse and can impair the health and productivity of animals, and result in economic losses for producers. The total alkaloid content, as well as the level of individual alkaloids, varies; therefore, it is difficult to obtain specific data on exposure to individual toxins of certain animal species as well as to set safe levels. Despite only a few countries have set limits for individual ergot alkaloids in food or feed, recommendations for levels of ergot sclerotium (dormant winter form of the fungus Claviceps purpurea) are being used. Thus, the limit refers to the weight of ergot kernels per total commodity weight, and not toxin concentration.
The use of high quality feedstuffs to reduce toxicosis of ergot alkaloids in livestock is the first step in avoiding problems they can cause, but to totally protect animals from the increasing risk of ergot alkaloid poisoning, the inclusion of a mycotoxin counteracting product could be considered.