Necrotic enteritis (NE), caused by netB toxin producing Clostridium perfringens type A strains, is an important disease in broiler chickens worldwide. Attempts to prevent necrotic enteritis by vaccination hitherto have insufficiently taken into account the practical limitations of broiler vaccination. Indeed, vaccination of broilers needs to be performed at day of hatch or in ovo. In most published studies on vaccination against necrotic enteritis multiple doses at different ages are administered, what is practically impossible for broilers.
In the current study, the efficacy of single and double subcutaneous vaccination using crude supernatant containing active toxin and formaldehyde inactivated crude supernatant (toxoid) of a netB positive C. perfringens strain was analyzed in a subclinical necrotic enteritis model. In addition, single vaccination at day 1 and day 3, and double vaccination at day 3 and day 12 post-hatch were compared.
Double vaccination with crude supernatant and toxoid resulted in a significant decrease in the number of chickens with necrotic enteritis lesions. However, protection induced by vaccination using toxoid was lower compared to active crude supernatant. Single vaccination with crude supernatant at day 3 resulted in significant protection, while vaccination of one-day old chickens with crude supernatant or toxoid, as required under practical conditions, did not induce protection.
In conclusion, treatment of crude supernatant of a particular C. perfringens strain with formaldehyde lowered the efficacy of the crude supernatant vaccine. The observation that vaccination of one-day old broilers with crude supernatant or toxoid was not successful indicates that practical application of vaccination of broilers to control necrotic enteritis may be problematic.