Overeating disease in sheep is actually a misnomer.
Instead, this disease is more accurately termed enterotoxemia, which is caused by the bacteria Clostridium perfringens. There are six types of Clostridium bacteria (A,B,C,D,E,&F), however, only Types B, C, and D are significant in sheep and lambs.
The infection of enterotoxemia caused by C. perfringens types B & C can lead to severe enteritis, dysentery, toxemia and high mortality in young lambs. Clostridium perfringens Type C can also cause enterotoxemia in adult sheep. Usually, lamb dysentery is seen in young animals under three weeks of age. The proper prevention of enterotoxemia is caused by Type C vaccination of the pregnant dam. Vaccination is recommended in the last third of gestation, with a booster four weeks after the first injection.
Clostridium Perfringens Symptoms
Clinical signs of acute lamb dysentery caused by C. perfringens Type C include lambs that stop nursing, become listless, produce blood tinged diarrhea or die within a few days. Many times, the lamb dies prior to exhibiting clinical signs of the disease. Treatment is usually ineffective, and the best course is prevention by vaccination of the pregnant dam.
Enterotoxemia caused by C. perfringens Type D is frequently found in lambs and, less likely, in goats. This is the disease most commonly referred to as the “Overeating Disease”. Typically, it affects young lambs under two weeks of age or the weaned lambs that are consuming a high-carbohydrate diet (grain). However, lambs grazing lush pastures are also susceptible. There are few signs of the disease apart from “Sudden Death Syndrome”. The term “overeating” was given to this disease because it affected many of the larger lambs consuming grain diets.
Clostridium Perfringens Treatment
Unfortunately, treatment is commonly ineffective. Thus, vaccination of pregnant dams and lambs is recommended. Lambs nursing ewes that have been vaccinated receive immunity through the ewe’s milk. Most sheep are found to have at least some population of C. perfringens in their digestive tract. When lambs begin consuming large amounts of carbohydrates (milk or grain) the bacteria flourish producing a waste product that is toxic and effects the central nervous system. Usually, the bacteria proliferate causing the toxin to be released within a short period. This causes the unvaccinated lamb to succumb to the disease, usually without clinical symptoms.
The recommended vaccination schedule is to initially immunize pregnant ewes in the last trimester of gestation with a booster about four weeks later and subsequent annual vaccinations. A young lamb’s immune system is not developed to allow the full effect of vaccination prior to four weeks of age. So, it is suggested that young nursing lambs be vaccinated with C. perfringens Types C & D at that point and again two to four weeks later. An annual vaccination is recommended to prevent occurrence of the disease in the adult animal.
Clostridium Perfringens Types C&D Toxoid Vaccine
It is also suggested that young lambs be vaccinated for Tetanus (Clostridium tetani) in conjunction with a vaccination for enterotoxemia. This can be accomplished by using a toxiod vaccine that includes C. perfringens Types C & D, and Cl. tetani (CD/T vaccine). It is important to note the difference between the toxoid vaccine and antitoxin. The C. perfringens Types C & D antitoxin provides protection almost immediately but gradually becomes ineffective after two weeks. In contrast, the toxoid vaccine typically builds immunity in a two-week period, and that immunity persists for approximately a year when given a booster two to four weeks after the initial vaccination.
When lambs are born to unvaccinated ewes and the organism is present, it is advised that they be treated first with antitoxin and then subsequently vaccinated with the toxoid vaccine for maximum protection.
When purchasing lambs from a breeder or through a club lamb sale, it is a very good idea to ask the breeder if the lambs have been vaccinated. If that answer is no, the new owner should vaccinate the lambs immediately and once again after two weeks.