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Different vaccination programs for infectious bursal disease (IBD) using live vaccines containing either mild Winterfield 2512 strain (10 to 3.5 power EID50/dose) or intermediate VMG 91 strain (10 to power 3.0 or 10 to power 4.0 EID50/dose) were compared in commercial broilers with maternally derived antibodies (MDA). Three broiler flocks (Ross) of 32, 000 birds each were housed in separated poultry houses on the same farm. One group (A) was vaccinated twice, at 8 and 13 days of age, with 10 to power 3.0 EID50/dose of VMG 91. A second group (B) underwent the same vaccination program but the birds had been vaccinated with Winterfield 2512 when they were one-day-old. A third group (C) was vaccinated according the same program as group B except they were vaccinated with 10 to power 4.0 instead of 10 to power 3.0 EID50/dose of VMG 91 on both occasions. All vaccinations were done via drinking water. Antibodies for IBD were assessed using IDEXX ELISA on the 1st, 8th, 13th, 23rd, 33rd and 43rd day of life. Chickens of all groups possessed MDA for IBD (1563 with st. dev. of 774, 1329 with st. dev. of 662 and 1023 with st. dev. of 721 in group A, B and C, respectively). The final titres were significantly higher if chickens were vaccinated with Winterfield 2512 when day-old despite the presence of MDA (3277 with st.dev. of 857 ELISA units in group B compared to 2326 with st. dev. of 678 in group A at 43rd day of life). Further, it seems that 10 to power 4.0 instead of 10 to power 3.0 EID50/dose of VMG 91 strain did not influence the final antibody titres (3352 with st.dev. of 911 ELISA units in group C at 43rd day of life), but higher content of the vaccinal virus was reflected in earlier antibody production (2413 with st. dev. of 773 ELISA units in group C compared to 1377 with st. dev. of 611 in group B at 33rd day of life). |
