The benefits of supplementation with antibiotic alternatives on Newcastle disease virus titres in poultry

Newcastle disease is one of the most important diseases of poultry with wide distribution and high fatalities. An infection with a virulent strain can cause up to 100% fatality in a susceptible flock, with devastating economic losses. In-feed antibiotics are not directly effective against Newcastle disease virus (NDV), but they may assist in prevent associated production problems. With in-feed antibiotics being controlled or banned, prebiotics, particularly those sourced from spices, and probiotics have been investigated as potential alternatives for maintaining seroconversion in poultry vaccinated against NDV. Certain prebiotics have a positive effect on anti-NDV antibodies but using spices as sources of prebiotics gave no clearly defined results. Garlic extract was reported to increase the mean haemagglutination inhibition (HI) titre of NDV by 0.6 after two weeks of supplementation, increasing titres by 4.0 in the vaccinated group compared to an increase of 3.4 in vaccinated unsupplemented group. However, onion-based compounds did not improve anti-NDV antibodies. The majority of studies have found that probiotics improved antibody levels and seroconversion to NDV vaccines in poultry. A commercial probiotic, containing a mixture of Bacillus species and Saccharomyces boulardii when used at a concentration of 100 g/ton was found to significantly increase the anti-NDV titre (log(2)) from 5.00 to 5.50. Another commercial probiotic, consisting of a combination of bacteria, reduced mortality by 6.6% at a concentration of 1 g/kg. Additional studies are needed to define the conditions and forms in which both the pre- and pro-biotics work best with respect to NDV control.