1.1 Background of the study
The poultry industry in Nigeria is characterized by a mixture of backyard, peasant, household-oriented and modern large scale poultry farms which dot our country side and urban centres today. It can be said that poultry keeping has become a business in Nigeria since Poultry is now kept by practically every household in Nigeria especially in rural communities (Obioha 1992). Broilers are meat type chickens that reach market size at about 8-10 weeks of age. Nearly 80% of all commercial chicks hatched in Nigeria are broilers (Bundy et al 1975).
Poultry occupies a unique position in Nigeria animal production programme for several reasons. The most important of these is the fact that poultry are relatively free from the many pathological, ecological and economic constraints which affect the commercial production of other breeds and classes of livestock in Nigeria (Obioha 1992). The occurrence of disease in a poultry flock is a serious event and one that causes a lot of anxiety to a poultry farmer due to the fact that most commercial poultry are reared intensively with a large number of birds occuping a relative small area, a disease can spread rapidly among the whole flock causing a high level of mortality and huge financial loss to the farmer. The prevention of disease therefore is a decisive factor to the success or failure of a poultry enterprise. Diseases of poultry can be caused by four major factors namely: pathogens, poor management, deficiency of nutrients and metabolic disorders. Most poultry diseases are brought about by the presence of one or more pathogens or causative organisms. These organisms are always present in any poultry environment but they attain a virulent stage when the resistance of the chicken is low due to internal or external stress. The stress condition may be created by mismanagement, transportation, handling, internal parasite or even excessive excitement (Obioha 1992). The infectious organism may also gain easy access to the tissue of the birds following wound that may be cause by cannibalism. Some of the common sources of stress are lack of feed and water, poor ventilation, inadequate floor space, poor sanitation, high internal and external parasitic load, extremes of weather, vaccination failure, sudden changes in feed or environment, pests, flies, ants, nutritional deficiencies etc.
Apart from encouraging the invasion of pathogens, bad management may cause disease directly. Examples of bad management are over crowding, poor ventilation, failure to vaccinate at the right time, failure to remove dead birds promptly, failure to remove droppings regularly leading to accumulation of ammonia and breeding site of pathogens and parasites, cannibalism, uncontrolled access of visitors to poultry farms and absence of disinfectant troughs or dips.
Poultry disease maybe caused by lack of or deficiency of one or more essential nutrients. This is why poultry feeds should be balanced. Where one element is deficient or excessive it can induce or cause the body to show symptoms relevant to such deficiency or excessesive availability of the nutrient. A group of diseases may be caused by faulty metabolic process in the body. These include the fatty liver syndrome. Animal diseases are important limitation to edible protein production. It is the goal of veterinary medicine to reduce losses due to animal diseases and in cooperation with animal scientists, to develop positive live stock /poultry health programme (Oyenuga et al 1973).
Vaccination of poultry is very important disease prevention programme in poultry farming. Vaccines have varying expiration dates, depending on the storage temperature and nature of production. The expiration date is based on holding the vaccine under optimum conditions, frequently involving refrigeration. Vaccines that are expired have lost part of their antigenic properties and are ineffective as immunizing agents. Vaccination of poultry animals are programmed based on age of birds and are administered based on age and body weight. Although vaccination is an important weapon in the control of many livestock diseases, the immunity produced is overcome by massive exposure of birds to infection, by moderate contact with a highly virulent strain of the infecting agent or by stress, e.g. poor environment conditions.
Moreover it is not the purpose of a vaccine to protect an animal that is inoculated while in the incubation stage of a disease. Vaccination should not be considered as a panacea in disease control. It should be supplemented with sanitary measures designed to prevent the introduction and spread of disease. Some poultry diseases can not be treated properly by medication but can be controlled by vaccination; therefore vaccination of poultry against certain diseases and at the right timing help in proper growth rate as well as reduced morbidity and mortality in the flock. Evidence has shown that there are delayed vaccination programmes for broilers reared by some farmers in remote villages or farmers that rear their birds in locations where veterinary care is limited or non existent; that is why this research is aimed at knowing the effect of those delayed vaccination on growth and mortality rate of affected birds.
1.2 Objectives of the Study
The objectives of this study are as follows
- To find out the effects of irregular timing of vaccination on the growth performance of broilers.
- To determine the mortality rate of broilers subjected to irregular vaccination schedules.
- To determine the Haemagglutination inhibition values and the Haematological values (Packed cell volumes and White blood cell counts) of birds not vaccinated at the appropriate times.
Vaccination is an effective means of preventing or reducing the adverse effect of specific diseases in poultry especially viral diseases. The control of viral disease is dependent upon prevention through sanitation, biosecurity and by vaccination. In some areas or small farms, vaccination is seldom practiced because of some reasons namely; low cases of disease problems in farms, lack of proper diagnosis and expensive cost of vaccines as poultry vaccines usually come in 100-1000 dose vials. Vaccines come in either live or inactivated forms which have their advantages and disadvantages. What normally brings about vaccination failure include, breaking the cold chain by poor storage since they come in freeze dried forms, exposing the vaccine directly to sunlight or heat and lack of adoption of proper route of vaccination. These can reduce the potency of a vaccine. The timing or schedule of vaccination can also affect the performance of the birds. These factors leading to vaccination failures abound with little or no information to the farmers as to why they occur and the extent of loss caused to the farmer. Nigeria is largely a country where minimum attention is paid to quality control or adherence to prescribed conditions for storage of drugs and for vaccines. As such, the poultry farmers and their enterprises are limitlessly at the mercy of agencies that procure vaccines/drugs and fail to adhere to manufacturer’s specifications about storage and shelf life since nobody actually monitors them to ensure that there specification are adhered to. The best that can be done to inform farmers could be to document the affects of vaccination failures to the birds being reared to create awareness which may lead to asking pertinent questions about storage life of each vaccine before procuring them for use in a poultry enterprise.