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.