The effects of different diets on haematological parameters of different species of poultry have been examined in this review. In Nigeria, different poultry species contribute to the animal protein supply of the populace in terms of eggs laid and meat produced. Feeding poultry for optimum growth production requires that the birds consume appropriate balanced diets for the health and productivity, it is important that they be fed diets that meet their nutritional requirements. Dietary components affect the blood profile of healthy birds. The blood transports or conveys nutrients and materials to different parts of the body. Therefore, whatever affects the blood, either nutrition or drugs will certainly affect the entire body adversely or moderately in terms of health, growth, maintenance and reproduction. Thus, a readily available and fast means of assessing, clinical and nutritional health status of animals on feeding trials may be the use of blood analysis, because ingestion of dietary components have measurable effects on blood composition.