Multi-Trait Estimation of Genetic Parameters for Body Weight and Feed Intake in a Commercial Broiler Chicken Population

Background: A high genetic improvement in the growth rate and feed efficiency of broilers has been recorded in the last five decades due to genetic selection.However, the increase in global human population, increasing demand for affordable animal protein, increasing feed costs, and continuing global environmental issues continue to push the broiler industry to produce broiler chickens that grow quickly and efficiently.To further improve the growth rate and feed efficiency of broiler chickens, it is necessary to understand the genetic background of growth rate (body weight) and feed efficiency in broiler chickens.Therefore, this study was conducted with the objectives of simultaneously estimating genetic parameters of body weight (BW), feed intake (FI), and body weight gain (Gain) in broiler chickens, as well as calculating residual feed (RFI) and estimating its genetic parameters.Methods: The data of 45 generations for growth rate in commercial broilers from the Arta Sablan Poultry Company of Ardabil Province were used for analysis to estimate genetic parameters for body weight (BW) in males and females at three different ages.Body weight data were measured at three different ages (day t, day t-4, and day t-7) of both sexes.The first BW was recorded on day t for 25 generations; however, as the selection continued, the birds began to grow faster and reach the desired BW earlier.Therefore, the age of weighing changed, and BW was recorded at t-4 and t-7.BW in males and females, and BW at two ages was considered separate traits in each of the three traits.This led to the creation of a 12-trait model for BW, FI, and Gain in two sexes and the three age groups.The phenotypic RFI trait (RFIP) was estimated from the conditional distribution of FI given BW and Gain using partial phenotypic regression coefficients.Similarly, genetic RFI (RFIG) was estimated from the conditional distribution of FI given BW and Gain using partial genetic regression coefficients.Genetic parameters of BW and feed efficiency were estimated using multi-trait REML analysis; hence, gender by genotype interaction and age by genotype interaction were examined for all traits: BW, FI, Gain, and RFI.Correlations between production traits and feed yield traits were also estimated here.Results: In males, the estimated heritability values of BW were 0.38, 0.34, and 0.29 on days t-7, t-4, and t of age, respectively.In females, however, the estimated heritability values of BW on days t-7, t-4, and t were 0.41, 0.38, and 0.38, respectively.The genetic correlations of BW between males and females on days t-7, t-4, and t were 0.95, 0.89, and 0.89, respectively, and the genetic correlation of BW was significantly different between ages.The average heritability of FI and Gain was moderate, and the estimates were significantly different in males and females at the same age for all traits.In addition, the genetic correlation between males and females at the same age was significantly different, indicating a genotype-by-sex interaction for BW and FI traits.The mean heritability estimates of RFIP were significantly higher than RFIG in both sexes and three different age groups.In addition, the genetic correlation between RFIP and RFIG was significantly different at the age of t days, but no significant difference was observed at the age of t-7 days.Estimates of the heritability of production traits and feed efficiency were obtained at an average level, and, therefore, they can be modified by genetic selection.