Serum immunoglobulin responses among broiler chickens fed Ugandan commercial poultry feeds and vaccinated against Newcastle disease.

Responses to the La Sota strain Newcastle disease (ND) vaccine virus were monitored in 240 Ross breed broilers fed 4 Ugandan commercial feeds, Fs, F1, F2 and F3. The production of IgM, IgG and haemagglutination-inhibition (HI) antibodies, were monitored from day 28 of age for 4 weeks using the ELISA assay and HI-test. All broilers were sero-negative before vaccination. The Fs, F1, F2 and F3 feeds had metabolisable energy/crude protein ratios of 599, 870, 823 and 685 respectively, and had significant (P < 0.05) differences in the development of IgM, IgG and HI titres. Commercial feed FI reduced IgM (31.9%); IgG (30.9%) and HI (54.5%) titres. Commercial feed F2 reduced IgG (30.2%) and HI (36.4%) titres but did not affect IgM. Commercial feed F3 reduced IgG (16.3%) but affected neither IgM nor HI titres. Peak HI titres of F1 (2(2.5)) and F2 (2(3.5)) were below the HI titre (2(5.2)) that prevents 100% mortality due to virulent ND virus infection. Per cent loss of IgM titres in broilers that had sero-converted was 100% (F1), 25% (F2), 25% (F3) and 20% (Fs) by week 4. Per cent loss of IgG titre was 12.5% (F1), 16.7% (F2), 7.2% (F3) and 4% (Fs) by week 5. However, none of the feeds affected the time of attaining maximum sero-conversion at week 2 (IgM), week 3 (HI titres) and week 4 (IgG) in the flocks. The lack of standardisation of poultry feed quality in Uganda may be a shortcoming in successful protection of poultry by vaccination against ND.