Dr. Kalen Cookson, Director of Clinical Research with Zoetis, speaks to The Poultry Site’s Sarah Mikesell at the 2024 IPPE in Atlanta, Georgia, USA.

Editor’s note: this interview has been edited for length and clarity.

You shared a poster at the International Poultry Scientific Forum (IPSF). Tell me about your research.

We investigated the effect that a late infectious bursal disease virus (IBDV) infection could have on infectious bronchitis immunity. There's no controversy that an early IBDV infection can cause profound immune suppression that is long-lasting. But there's a lot of mixed opinions about a late infection occurring at or after three weeks. We wanted to do a study to investigate because we have felt that there's at least temporary immune suppression that can occur. We don't know how severe it can be, so we wanted to measure it in a model that we've well-established with infectious bronchitis.

What was the effect of IBD on susceptibility to infectious bronchitis?

We took the most prevalent IBD variant virus in the US called AL-2, and we administered it at three weeks of age to birds that had been vaccinated for infectious bronchitis at day of age by spray, using Mass and GA08, the most common commercial program today. Then we came behind the IBDV challenge with the most prevalent infectious bronchitis virus, DMV/1639, at 25 days or 4 days later.

What we found is Mass and GA08 vaccination gave significant protection against DVM/1639, measured at 31 days, even when there was an IBDV challenge, but the amount of protection afforded was less and, in some cases, significantly less if the birds had an IBDV challenge before the infectious bronchitis challenge.

We did demonstrate that at least in the temporary window four to 10 days after the IBDV challenge, there was a temporary dip in immunity. We don't know how long it lasts, but at least in the context of the study, that's what we found.

If a solid breeder program can only get IBDV protection for up to three weeks, but an infection after that time can still cause temporary immune suppression, what other options are there to minimize the impact of a late IBDV infection?

Everyone tries to have a very solid breeder program with the idea of protecting during the first three weeks with maternal antibodies. It's the most efficient way to prevent early infections, and it's the time when IBD infections can cause the most damage to the immune system.

But in this study, the day of age maternal antibodies were fairly high – over 7,500 geometric mean titer. This is pretty representative of most commercial broiler flocks, but by three weeks of age even high titers are pretty well-depleted – and that's what we see in the field. Most people are on a good breeder program, and their window of IBD challenge is right around three to four weeks of age because the maternal immunity can only last so long.

If you have a late IBD infection and then you have an infectious bronchitis challenge, which is very common, what else can you do to minimize the sting that an IBD challenge might have at that time? The only thing to do would be to vaccinate the broilers themselves. You can either give a live vaccine in the hatchery in ovo, you could give a recombinant vaccine, or you could do some field vaccination. But most people would opt to vaccinate in the hatchery with what we have available.

Do you plan to look at vaccination of the broilers using this model?

Yes, in fact, we did have a recombinant treatment overlaid into this study. We did not present it at this meeting because we tried to just focus on the IBD susceptibility and the effect on infectious bronchitis protection. But we'll be expounding on the overall study that we conducted and presenting that at later meetings this spring. What we basically saw was the birds that also received in ovo recombinant HVT-IBD vaccine had a full restoration of DMV/1639 protection as was seen in the Mass and GA08 vaccinated controls (no IBDV challenge).