HEAL ▶▶▶TH
Preventing vaccination failure
Vaccines are used to prevent disease outbreaks when a flock is exposed to field disease organisms. From time to time, vaccination failure occurs when chickens do not develop adequate antibody titer levels or are susceptible to a field disease outbreak following vaccine administration. Poultry World sums up the factors necessary to avoid inadequate vaccine protection.
BY SALAH H. ESMAIL W
Feed quality is a factor that is often over- looked when it comes to vaccine efficacy.
hen a vaccination fails, the quality of the vac- cine is typically blamed. Although this is cer- tainly an important consideration, there are other factors that must be evaluated to de-
termine the cause of the failure. A thorough understanding of these factors will help prevent losses associated with vaccination failure.
Maternal immunity A high level of maternal antibodies in the young chicken may interfere with the multiplication of live vaccines thereby reduc- ing the level of immunity provided. For example, if a chick comes from a breeder hen with high levels of antibody against Gumboro (infectious bursal disease), the chick will typically have high levels of (maternal) antibodies for several weeks. If vaccination is attempted while these antibodies are still
present, some of the vaccine viruses will be neutralised and re- sponse to the vaccine results will be diminished. On the other hand, delaying vaccination until the maternal antibodies have catabolised may leave the birds susceptible to field challenges.
Feed factors The presence of mycotoxins in poultry rations can impair the immunity acquired through vaccination and eventually lead to diseases occurring, such as infectious bursal disease virus (IBDV) or Adenovirus. Mycotoxins induce immunosuppres- sion by depressing T or B-lymphocyte activity, impairing mac- rophage/neutrophil-effector functions, reducing the level of antibodies and the activity of phagocytic cells following vac- cination. This then and increases the production of steroids from the adrenal glands which decreases lymphocytes and increases neutrophils. Poultry producers therefore need to keep feed troughs free of mould and control mould growth by using mould inhibitors containing acetic acid, sorbic acid, and propionic acid.
Environmental factors Under heat stress conditions, corticosterone is released by the hypothalamus–pituitary–adrenal axis. This hormone has been shown to deregulate both the lymphocyte phenotype charac- teristics and total antibody production in broiler chickens. Chickens exposed to heat stress (38 ± 2°C) over long periods of time will thus have impaired vaccine responses and conse- quently will be susceptible to pathogenic environmental chal- lenges. Therefore they should be kept in a thermo-neutral environment, especially in the early stages of their life. If the ammonia level in the house is high (above 100 ppm), this too will have a negative effect on the bird’s ability to pro- duce local immunity, as the cells on the surface of moist membranes are adversely affected. In the absence of local immunity, the bird becomes susceptible to viral diseases, particularly those which proliferate in the respiratory tract. Ammonia concentration can be controlled by the following management and feeding strategies: • Management: Ammonia problems can be alleviated with management practices, such as the use of nipple drinkers, balancing bird density with ventilation facilities and using litter materials with a high water-retention capacity. • Protein nutrition: Feeding reduced protein diets (2%
8 ▶ POULTRY WORLD | No. 1, 2020
PHOTO: JAN WILLEM SCHOUTEN
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