Slower growing breeds of broilers in free-range systems need a different vaccination regime from that of faster-growing broilers, when being immunised against Gumboro disease.

This finding has emerged from laboratory and field trials, involving several hundred thousand birds on farms throughout the UK, carried out by Lohmann Animal Health in conjunction with poultry vets.

“When using a ‘hot’ vaccine, conventional broilers in the UK are normally vaccinated at around 14-16 days when their maternal immunity is waning,” said Lohmann’s Adam Goddard. “However, we’ve found this maternal immunity lasts longer in the slow-growing breeds when reared both indoors and out.”

Realistically, the correct day of vaccination for free-range table birds is more likely to be achieved by using the vaccine date predictions for broiler breeders, rather than that of broilers, under the Deventer formula, which gives calculations for different types of bird.

He therefore advises producers to consult their vets who can take blood samples to get an accurate prediction regarding optimum timing of vaccination with their own particular flocks.

“Our trials have shown that, in general, and depending upon the breed used, the decline in maternal immunity is delayed – perhaps for 4-5 days. So, in order to get a better ‘take’, we recommend vaccinating these birds later or using a vaccine that ‘takes’ in the presence of high maternal immunity,” said Mr Goddard.

Gumboro disease – also known as infectious bursal disease – can cause severe losses in chickens and outdoor-reared birds are more susceptible to the disease due to environmental influences.