Abstract

This study was carried out to determine the effect of varying levels of methionine supplementation in di et of broiler chickens on their immunological response to Newcastle disease , growth performance , organ characteristics and haematological parameters . A total of two hundred birds were raised from day - old to six (6) weeks . T hey were distributed into four treatments A, B, C and D with five replicates per treatment, each replicate having 10 birds. At both starter and finisher phases of the experiment, there were four experimental diets A, B, C and D. Diet A was the control diet and contained a standard of 0.38% methionine , diet B wa s the diet containing 0.5% methionine as permitted by National Research Council ( NRC ) standards while diet s C and D contained 0.63 % and 0.75% methionine supplementary levels , respectively. By the third week of the experiment, some of the general observations made include d leg weakness which later progressed to complete paralysis in about 40% of the birds placed on diet C and D . Mortality occurred in 70% of the paralysed birds. The immunological responses after vaccination with Newcastle disease vaccine intra - ocular ( NDV i/o ) revealed that chickens fed with 0.5% methionine ( treatment B) recorded the highest antibody titre value ( log 2 7 ) while treatment D (fed with 0.75% methionine) had the lowest mean titre value (log 2 5 ). Thereafter, administration of NDV LaSota elicited immune responses with antibody titre values being highest in treatment B (log 2 9 ) and least in both treatments A and D (log 2 7 ). T he performance characteristics such as the final body weight (FBW) , weight gain (TWG) , feed intake (TFI) and feed conversion ratio (FCR) showed significant (p<0.05) differences among the various dietary treatments , with birds on NRC requirement methionine based diet having significantly (p<0.05) higher FBW, TWG, FCR and TFI than those fed the rest test diets throughout the experimental period. Relative weight of the organs liver and gizzard were also significantly (P< 0.05) different between treatment groups. Among the haematological variables only the red blood cell count ( RBC ) , mean corpuscular haemoglobin ( MCH ) and mean corpuscular volume ( MCV ) values were significantly different (p<0.05) among treatment groups in the starter phase of the experiment and erythrocyte sedimentation rate ( ESR ) , basophil and eosinophil in the finisher phase . It was concluded that methionine supplementation at this high inclusion levels is detrimental to the immune response, growth performance, nutrient utilization and organ characteristics of broiler chickens .

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