Recombinant vaccine technology has brought more convenience and safety to poultry health programmes. The only hitch: two recombinant vaccines made with the herpesvirus of turkey (rHVT) could interfere with each other if used in the same flock. Producers, therefore, need to choose their battles carefully and determine which disease problem warrants this superior technology.

“You have to look at the big picture and use recombinant vaccines strategically,” says Marilynn Finklin, DVM, poultry technical service manager for Merck Animal Health.

“Since poultry need protection against multiple diseases, you need to carefully determine which diseases are best controlled with a rHVT or with conventional live vaccines.”

The veterinarian pointed to a recent field trial conducted with a US integrator to illustrate her point.

Evaluating Options

The producer wanted to determine the best vaccination programme for six-pound broilers. The goal was to protect flocks against infectious bursal disease (IBD) as well as Newcastle disease (ND) and the Massachusetts and Arkansas strains of infectious bronchitis (IB) virus. The IBD virus affecting the integrator’s farms was primarily a variant population; the respiratory challenge at the time of the trial was not significant, Dr Finklin says.

The farm tested two vaccine protocols:

Protocol A

• rHVT IBD vaccine via in ovo injection
• Live ND vaccine via spray cabinet
• Live Mass/Ark IB vaccine via spray cabinet

Protocol B

• 89/03 live IBD vaccine with the Delaware strain, administered in ovo
• Innovax ND-SB, a rHVT vaccine, administered in ovo
• Live Mass/Ark IB vaccine via spray cabinet

In Protocol A, the live ND vaccine administered with a spray cabinet could result in field spread of the virus and has been associated with so-called “rolling respiratory reactions,” Dr Finklin says. The live Mass/Ark IB vaccine administered via spray cabinet has the potential to cause mild reactions.

Protocol B, on the other hand, was designed to minimise reactions. 89/03, a live IBD vaccine with a Delaware variant strain, causes no reactions when administered in ovo. The recombinant vaccine Innovax-ND-SB provides immunity against ND and Marek’s disease and causes no reactions; it can be administered in ovo to day-old chicks. (The vaccine is also available as Innovax-ND, which does not contain the SB-1 strain of chicken herpesvirus serotype 2.)

The producer then looked at average daily gain, final weight and the feed conversion ratio (FCR) to evaluate the results of the two programs. Bursal health was also evaluated based on histology, which was conducted on bursas taken at three farms from each vaccination programme at 7, 14, 21, 28 and 35 days of age.

Results

The FCR was similar for both groups, Dr Finklin says, but broilers on Protocol B, featuring 89/03, had better average daily gain and a better final weight (Table 1).

Figure 1. Bursal histopathology results at 21 days of age; 1=good and 4=atrophy.

All sampled bursas were healthy on days 7 and 14. “This is the time when maternal antibody protection is greatest,” Dr Finklin adds. By day 21, however, bursas from the recombinant IBD vaccine group (Protocol A) had significant atrophy (Figure 1). On day 28, bursas from both groups had evidence of bursal damage, with higher scores in the rHVT vaccine group.

“In this trial,” she says, “the live IBD vaccine provided a longer duration of protection and resulted in milder bursal lesions than the rHVT vaccine, which was clearly demonstrated by histological results.”

In a recent study, the efficacy of rHVT IBD was compared to that of 89/03. As in the field trial, the predominant IBD challenges were Delaware-type variant viruses; the bursas of broilers that had received the rHVT IBD vaccine showed acute IBD virus pathology one week before the 89/03 vaccinates.

“There isn’t a single vaccination programme that’s right for every poultry farm and there are lots of good tools available for managing disease,” Dr Finklin says.

“The point is, you need to have a strategy. With the recombinants, it’s more than just selecting a vaccine for a particular disease. You also need to consider the tools you have available for managing the other diseases in your flock. If you can control one disease effectively with traditional vaccines, then save the recombinant for the tougher disease on your list.”

Further Reading

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