VARIATION IN SELECTEDGROWTH-INFLUENCING GENES AND THEIR ASSOCIATION WITH GROWTH, CARCASS CHARACTERISTICS AND THERMO-TOLERANCE OF INDIGENOUS CHICKENS IN NIGERIA

Abstract

Slow growth rate and acute heat stress are the main constraints to Indigenous Chicken (IC) production in Nigeria. Characterisation of growth-influencing and heat-tolerance genes are requisites for selective breeding of poultry for improved growth, carcass traits and heat-tolerance. However, information on the variation in growth-influencing and thermo-tolerance genes of IC in Nigeria is inadequate. Therefore, variation in some growth-influencing genes and their association with growth and heat-tolerance traits of IC in Nigeria were investigated.

One-day old chicks(n=358) comprising 118 Yoruba Ecotype Chicken-YEC, 102 Fulani Ecotype Chicken-FEC and 138 FUNAAB Alpha Chicken-FAC were tagged and fed ad libitum on commercial diets for 24 weeks. The bodyweight (g) of each chicken was measured weekly. At week 12, blood (5 mL) was sampled from all surviving 96 YEC, 89 FEC and 113 FAC. Genomic DNA was extracted, amplified and electrophoresed using standard procedures. Myostatin, ghrelin, Heat Shock Protein-70 (HSP70), Pituitary Transcription factor-1 (PIT-1) and myogenin genes were genotyped using Alu1, Hinf1, Mme1, Msp1 and EcoR1restriction endonucleases, respectively. Association between variants of the genes and weekly bodyweight of each chicken were assessed. At week 23, six chickens per identified HSP70 genotypes (AA, AB and BB) selected from each of YEC, FEC and FAC were exposed to 40±1°C for one hour and blood (5 mL) was sampled and analysed for Packed Cell Volume-PCV and erythrocyte. Cloaca temperature was recorded and Heat Stress Index (HSI) calculated. At week 24, 40 chickens from each of YEC, FEC and FAC were randomly selected and sacrificed. Thigh, breast and dressed weights(g) were measured. Data were analysed using descriptive statistics and ANOVA at α0.05. The bodyweight of FAC (2323.6±258.4) was heavier than YEC (998.2±159.0) and FEC (1156.2±181.3). Co-dominant alleles A and B with corresponding genotypes: AA, AB, and BB were detected in myostatin, ghrelin and HSP70 genes. Genotypes AA and AB were observed in PIT-1 while myogenin was monomorphic. The bodyweight of FEC AB-myostatin genotype (627.7±86.2) was higher than 576.0±51.7 (BB-myostatin) and 582.4±80.8 (AA-myostatin) at week 12. Weekly bodyweight of YEC AA-myostatin genotype was similar to those of AB-myostatin and BB-myostatin. The bodyweight of FAC AB-myostatin genotype (1257.9±30.3) was significantly higher than 1160.5±24.3 (AA-myostatin) and 1094.4±43.4 (BB-myostatin). The bodyweight of FEC BB-ghrelin genotype (618.4±24.1) was significantly higher than 566.4±17.1 (AB-ghrelin) but similar to 607.3±9.2 (AA-ghrelin) at week 12.The PCV,erythrocyteand cloaca temperatures were similar for YEC, FEC and FAC. Within FAC, HSI of BB-HSP70 (1.35±0.03) was significantly lower than 1.59±0.08 (AA-HSP70) but similar to 1.46±0.02 (AB-HSP70), while within FEC, BB-HSP70 (1.32±0.05) had significantly lower HSI than 1.48±0.13 (AA-HSP70) but similar to 1.40±0.04 (AB-HSP70). In YEC,HSI of AA-HSP70 (1.44±0.06), AB-HSP70 (1.37±0.11) and BB-HSP70 (1.42±0.08) were similar. Dressed weight of FEC AB-myostatin (864.7±54.3) was higher than 792.1±18.9 (AA-myostatin) and 777.7±0.5 (BB-myostatin). Genotypes AA and AB (PIT-1) did not have significant effect on thigh and breast weights of YEC, FEC and FAC. The growth-influencing genes were polymorphic except myogenin which was monomorphic. Genotype AB-myostatin was associated with growth and carcass traits while BB-HSP70 was associated with thermo-tolerance.