Association between Insulin Like Growth Factor-1 (IGF-1) gene polymorphism and carcass traits in improved Nigerian indigenous chickens

The insulin-like growth factor-1 (IGF1) is a key regulator of muscle development and metabolism in birds and other vertebrate. Our objective was to determine the association between IGF1 gene polymorphism and carcass traits in FUNAAB Alpha chicken. Genomic DNA was extracted from the blood of 50 normal feathered birds. At 10 weeks, the birds were slaughtered for carcass traits. Specific primers for chicken IGF1 were used for amplification of a 622 base segment. The amplified gene products were digested with Hinf1 restriction enzyme and the digested fragments were genotyped. Allele frequencies were 52% and 48% for A and B, respectively. Genotype frequencies were 27%, 50% and 23% for AA, AB and BB genotypes, respectively. All carcass traits values and the IGF1 gene polymorphism observed were subjected to analysis of variance and the mean were separated using Duncan Multiple Range Test. The results showed that the occurrence of the polymorphism did not affect all the carcass traits but AB genotypes had the highest carcass traits values than the AA and BB genotypes. The conclusion of this study demonstrated that IGF-1 gene, to some extent, could be a candidate gene that affects carcass traits in Improved Nigerian indigenous chicken.

These findings have led to the conclusion Materials and methods that the indigenous chickens have a great potential Experimental birds and study location for meaningful genetic improvement for growth and The experiment birds consist of fifty (50) therefore contribute to the reduction of protein Nigerian improved indigenous chickens. The dearth in the country (Ikeobi et al., 1996). experiment was carried out at the Poultry breeding unit FUNAAB Alpha strains of chicken was developed at of the Directorate of University Farm (DUFARMS) and the Poultry Breeding units of the Directorate of the the Biotechnology Center Laboratory of the Federal University farm, Federal University of Agriculture, University of Agriculture, Abeokuta (FUNAAB), Ogun Abeokuta, Ogun state in Nigeria. The selection state, Nigeria. The University is located within latitude o o process for the traits of interest which is the meat 7 10'N and longitude 3 2'E and lies in the south western o and the egg started around 1997 with over 10 part of Nigeria. It has an average temperature of 33.7 C generations of selection for improved meat and egg and relative humidity of 80% with rainfall of about 1037 production.
mm. The egg type is a dual purpose which was The vegetation in the University represents an developed through a rigorous, systematic and interphase between the tropical rainforest and the selective breeding of the Nigerian indigenous derived savannah (Goggle Earth, 2016). chicken without eroding their tropical adaptive features and disease resistance traits.
Blood collection The potential variability that exists among For DNA extraction, blood samples were the indigenous chickens were utilized to upgrade collected in EDTA-treated tubes from the 10 week-old them. They still maintained the different plumage birds before slaughter. Samples were collected using a colours and the three feathering pattern (Normal syringe from the right jugular vein with a new needle feathered, frizzled feathered and naked neck) and syringe for each individual to avoid cross exhibited by the Nigerian Indigenous chicken.
contamination. The average chick weight at hatch is between 30 -35 g, age at first lay ranged between Genomic DNA Extraction and Quantification 16 -18 weeks, average body weight at first lay is DNA was extracted from the whole blood using between 1200 g -1728 g, and weight of first egg at Qiagen DNA extraction kit following the manufacturer lay is between 35 -40 g. The average egg laid per protocol. The purity and concentration of the extracted year ranges between 200 -250 eggs. D N A w e r e d e t e r m i n e d u s i n g N a n o -d r o p This increasing interest in genetics and animal spectrophotometer. breeding has led to several researches on how to improve both productive and reproductive traits in PCR-RFLP assay: chicken. Some of these productive traits include The PCR primers specific for the chicken IGF-1 leanness of chicken carcasses, changes in body g e n e w e r e u s e d ( F o r w a r d : 5weight and linear body parameters. The DNA amplification by PCR of each bird was chromosome 1 affecting abdominal fat weight has performed according to the following conditions: the been detected in chicken (Ikeobi et al., 2002).
PCR was performed in a total volume of 20 µl, According to Zhou et al. (2005) revealed four exons containing 2 µl of genomic DNA, 2µl of forward and and three introns. This gene is said to be a reverse primer (10pmol/µl), 4 µl of 5X Firepol PCR candidate for growth, body composition, premix and 12 µl of nuclease free water. Cycle metabolism, carcass characteristics, growth of parameters were 94ºC for 5 min then 35 cycles of 94°C adipose tissue and fat deposition in chicken.
for 45 sec, 60 ºC for 45 sec and 72ºC for 1 min, with a Therefore, IGF-1 gene could be a very final extension step for 10 min at 72ºC, the PCR useful physiological indicator to assist in screening products with length 622 bp were digested at 37ºC for and selection of animals at an early stage of growth. five (5) minutes with 10 U of Hinf1 restriction enzyme. (Afolayan and Fogerty, 2008). Hence, this study Restriction digests were electrophoresed at 100 was conducted for identification of the IGF-1 volts for 1h on a 2% agarose gel with ethidium bromide polymorphism and its possible association with and individual PCR-RFLP fragment sizes in each sample carcass traits in improved Nigerian indigenous were determined based on a standard DNA molecular chicken.
weight marker (100bp) by viewing the banding pattern under UV light on the transiluminator. All the three genotypes (AA, AB and BB) were found.

Data collection
The analysis of variance of effects of IGF-1 gene At 10 weeks of age, the Live Body Weight (LBW) of the birds from which the blood samples polymorphism on carcass traits showed that it had no were collected was determined and slaughtered. significant (P>0.05) effect on the live body weight The weight of the following carcass traits were also before slaughter (1000.63±97.02 g), the bled weight determined using a sensitive scale: Bled weight, (964.86±93.89 g), the plucked weight (904.87±87.87), Plucked weight, Eviscerated weight, Whole gizzard the eviscerated weight (722.93±73.75 g), the thigh weight, Empty gizzard weight, Liver weight, Wing weight (102.30±11.04), the breast weight weight, Leg weight, Thigh weight, Drum stick (154.70±17.60) and the back weight (145.96±16.12) weight, Neck weight, Breast weight, Back weight for genotype AB, although higher mean values were and Head weight.
observed in these and every other traits considered but the effects were not significant ( Moreover, the lowest mean values were also observed in the genotype BB for all other traits except for the plucked weight (644.57±194.03), the leg weight (30.71±9.07), the breast weight (99.57±39.09) and the head weight (29.14±5.66) which were higher than Where; P = the gene frequency of allele A, q = the genotype AA but less than AB, yet the differences were gene frequency of allele B, N = the total number of not significant. birds Allele and genotype frequencies observed in Obtained results were processed and the analysed samples are given in was the lowest among all loci (0.23) whereas AB is the population mean, Gi is the fixed effect of i genotype had the highest frequency of 0.50 as shown in IGF1 genotype and E is the random error  Where P> 0.05 show that the value is not significant ns = non significant