Leading experts and research scientists from around the world attended this year’s Avian Forum in Rome, organised by Merial. Dr Francesco Prandini DVM, Merial Avian Technical Director for Europe, Middle East and Africa, presented a paper on the effects of vaccination with VAXXITEK HVT+IBD on the immune system of commercial layer pullets compared with two modified live Infectious Bursal Disease vaccines.

Dr Francesco Prandini DVM, Merial Avian Technical Director for Europe, Middle East and Africa,

Dr Prandini says the results of the study show that the Merial vaccine VAXXITEK HVT+IBD protects the immune system of chickens against the immunosuppressive effects of Marek’s Disease and IBD, resulting in improved responses to other vaccines.

A total of 160 commercial brown pullets were split into four groups of 40 birds and reared in isolation rooms from day-old to 10 weeks of age.

• Group 1 was vaccinated with VAXXITEK HVT+IBD by subcutaneous injection at day old.
• Group 2 was orally vaccinated with an intermediate IBD modified live vaccine (MLV) at 28 days, after IBD maternally derived antibody levels (MDA) were below IBD ELISA titres of 250.
• Group 3 was eye-drop vaccinated with an intermediate plus IBD MLV at 28 days, after IBD MDA were below IBD ELISA titres of 250.
• Group 4 was not vaccinated against IBD as a control group.

All groups of pullets were vaccinated at day old with a Rispens vaccine by subcutaneous injection and with H120 against Infectious Bronchitis and Avinew® against Newcastle Disease (ND) by eye-drop. At day 14 all groups were vaccinated with the IB 793B variant vaccine Gallivac® IB88 by eye drop, and at day 21 they all received a second Avinew® vaccination.

Blood samples were taken on day 28 before the pullets were vaccinated with MLV IBD vaccines in groups 1 and 3 and from all groups on days 42 and 70.

The experiment was terminated at 70 days post hatch, when the bursa and body weight ratios were determined. Pullets vaccinated with VAXXITEK HVT+IBD showed significant higher bursa to body weight ratios than the other groups of the study, according to Dr Prandini. The bloods samples were analysed for the relative number of circulating B lymphocytes by flow cytometric analysis.

On day 28 there were no significant differences in the relative number of circulating B cells between the group vaccinated with VAXXITEK HVT+IBD (group 1) and non-IBD-vaccinated control pullets (group 4).

Thirteen days post vaccination with modified live IBD vaccines the pullets from group 2 (vaccinated with an intermediate MLV IBD) and group 3 (vaccinated with an intermediate plus MLV IBD vaccine) showed significant lower percentages of circulating B cells compared with the VAXXITEK HVT+IBD group and the control (figure 1).

Figure 1: Flow cytometric analysis of peripheral blood leukocytes for circulating B cells at 13 days post MLVs vaccination. *Indicates significant differences to the other groups (p < 0.05; ANOVA).

At 70 days, ELISA results for IB, Egg Drop Syndrome (EDS) and ND, along with ND HI titres, confirmed that pullets vaccinated with VAXXITEK HVT+IBD developed higher antibody titres against the three viruses following booster vaccination with the inactivated multivalent vaccine Gallimune 302, at 42 days of age, as compared with the MLV IBD vaccinated pullets in groups 2 and 3.

In summary, pullets vaccinated with VAXXITEK HVT+IBD did not show any depression of the number of circulating B cells, but pullets vaccinated with modified live IBD vaccines induced a significant reduction of relative B cell numbers.

Antibody levels against NDV, IB and EDS at 70 days were significantly lower in the groups vaccinated with modified live IBD vaccines compared with the VAXXITEK HVT+IBD group and modified live IBD vaccines may have affected the humoral immune response of the pullets vaccinated.

Further Reading Find out more information on the diseases mentioned in this article by clicking here.