As more producers suffer serious economic losses from Spiking Mortality Syndrome in turkeys (SMT), scientists continue to search for key information about the disease.
Unanswered questions range from causes to prevention to treatment, notes Dr. H. John Barnes at North Carolina State University's College of Veterinary Medicine. What scientists do know is that the disease typically affects poults between the ages of seven and 28 days, that it is infectious and transmissible, and that it is highly seasonal, normally flaring up from May into October.
The two clinical characteristics are severe stunting and mortality rates that reach at least one percent for three consecutive days. However, mortality rates have risen to 60 percent in the field and to 100 percent in experimental settings. Even when mortality rates stay at the low end, growth depression is severe, and flocks have a severely impaired ability to respond to later bacterial blood infections.
Recent work at North Carolina State University has shown that SMT is not simply a severe case of poult enteritis. The same studies have shown that SMT and Excess Mortality of Turkeys (EMT), which has lower mortality rates but similar stunting to SMT, are different clinical manifestations of the same disease.
The current theory is that SMT and EMT are due to an interaction of bacterial and viral infections complicated by protozoal infection. Birnavirus and coronavirus are now the viruses most suspected of being causative agents, says Dr. Frank Edens of North Carolina State.
Other work has isolated two strains of atypical E. coli from organs of poults suffering from SMT. Both strains tend to depress growth and cause increased mortality rates, Edens says. Cryptosporidia may be a contributing factor as well, Barnes says. When SMT has resulted in exceedingly high levels of mortality, Cryptosporidia have generally been present.
Whatever the causes of SMT turn out to be, scientists report that those which result in stunting appear highly transmissible and resistant, while those which cause mortality appear to be less so. Current treatment is limited to supportive care, Barnes says. He offers this advice for treating SMT:
1. Carefully formulate and monitor the diets of birds in the affected age group to keep them eating. Diets with high fat content (approximately 7.5 percent) have recently appeared to reduce early mortality rates. Increased carbohydrates, decreased protein and probably increased fiber may be helpful in poults less than 10 days old.
Also, sweet feed can help keep affected poults eating by increasing palatability. Small firm pellets and good crumbles with few fines increase palatability, while high levels of dry fines discourage feed consumption even more than usual, given the poults' dehydrated status. Dr. Peter Ferket, also at North Carolina State, suggests that as soon as flocks become loud and restless--the earliest signs of SMT--the grower should turn off the birds' water for two to three hours and dispense calf milk replacer into the drinkers until all the birds have been able to drink their fill. This treatment should be repeated on the following two days, Ferket says. He explains that the casein in the milk replacer helps "tighten" the birds and also supplies lactose to encourage the proliferation of Lactobacillus reuteri, which acts to competitively exclude pathogenic organisms.
2. Increase vitamin supplementation and electrolyte feeding to help decrease the impact of the disease. At the age when SMT normally hits, young poults would already have the lowest tissue levels of fat-soluble vitamins, according to other research. Poults with adequate vitamin levels through increased supplementation before the onset of the disease may fare better, Barnes says.
Because poults continue to drink after they have stopped eating, Barnes recommends supplying the supplemental vitamins through the water rather than feed. B vitamins help stimulate appetite, and vitamins A and E--especially E--could help enhance immune resistance, he notes. Vitamin D3 supplementation may also be more important than usual because the bones of afflicted poults are extremely brittle.
Edens notes that vitamin A supplementation in association with vitamin E is important because vitamin A is required for epithelial cell repair and proliferation in the intestinal tract, which may be severely damaged during SMT.
If serious diarrhea persists, Ferket recommends a rehydration solution including water, salt, sodium bicarbonate, potassium chloride and dextrose.
3. Maintain high levels of general management. Increased ventilation and a higher ambient temperature should both be goals, Barnes says. Dumping feed pans, cycling feed lines, making sure water is clean and getting birds up and moving frequently may improve feeding activity, he adds. Keeping litter dry also appears to limit mortality rates. Thorough cleaning and disinfection between flocks has generally prevented recurrence of high mortality, but has had little effect on stunting.
Strict biosecurity is important to help control the spread of the agents from one farm to another and from one flock to another.
References:
- Barnes, H.J. 1995. Spiking mortality of turkeys and related disorders. North Carolina State Univ.
- Edens, F.W. 1994. Physiological changes related to early poult mortality. Proc. 21st Annual Carolina Poultry Nutrition Conference. p. 46.
- Ferket, P.R. 1995. Effects of nutrition on spiking mortality and other enteric problems. North Carolina State Univ.
