A selection experiment was carried out for four generations (base and three selected generations) during the period from November 2011 to May 2015 in the Faculty of Agriculture, Benha University to improve egg production and quality traits in Benha chickens. A total of 18 cockerels and 180 pullets were selected according to their BLUP values for egg number during 90 days of laying from Benha base generation (G0). Each selected cock was mated with 10 selected hens and housed separately in breeding pen to produce the first generation of selection (G1). Then, selection was practiced for two generations to produce the 2nd (G2) and 3rd (G3) generations of selection. The pedigreed eggs from each individual breeding pen for the three selection generations (G1, G2 and G3) were collected daily for fifteen days and then incubated. The selection effects and correlated responses across generations were quantified and the genetic and phenotypic trends for egg production and quality traits in Benha chickens were clarified applying the updated approach of the animal model program of BLUPF90. Data of 756 hen produced by 69 sires and 484 dams were used to estimate heritabiliets, genetic and phenotypic correlations and BLUP estimates for age (ASM) and body weight at sexual maturity (BWSM), weight of the first egg (WFE), egg number (EN), rate of laying (RL), egg mass (EM) recorded during 90-days (EM90D) and 120-days (EM120D) of production after sexual maturity. Partial recording for egg number and egg mass during two days per week (EN2DW, EM2WM) and one week per month, (EN1WM, EM1WM) were identified. Pause periods in days during the first 90 days and 120 days (PP90D and PP120D) of egg production were recorded. A 4242 eggs were collected from all generations to study egg quality traits such as: egg weight (EW), albumen weight (AW), yolk weight (YW), shell weight (SW), Haugh unit (HU), egg shape index (ESI), albumen index (AI), yolk index (YI) and shell thickness (STH). Body weights of 4916 chicks were recorded at hatch (BW0), 4 weeks (BW4), 8 weeks (BW8), 12 weeks (BW12), and 16 weeks (BW16) of age, while the daily gains in weight for these chicks were calculated during the periods of 0-4 (DG4), 4-8 (DG8), 8-12 (DG12) and 12-16 (DG16) weeks of age. The aims of this study were: 1) to estimate the genetic parameters for egg production, egg quality and growth traits in such selection experiment, 2) to estimate BLUP values across generation, 3) to quantify the selection effects on different traits using generation contrasts estimated by generalized least square procedure, 4) to detect the phenotypic and genetic trends across generations, and 5) to estimate the direct selection response in egg number during the first 90-days of laying and the correlated responses in some egg and growth traits over three generations of selection in Benha chickens.
The results of this selection experiment can be summarized as follows:
First: Egg production traits:
1. The estimates of h2 were mostly moderate; being 0.27, 0.32, 0.42, 0.31, 0.34, 0.28, 0.33, 0.14 and 0.19 for egg production traits of ASM, BWSM, WFE, EN90D, EM90D, EN120D, EM120D, RL90D and RL120D, respectively.
2. ASM was closely positively genetically correlated with BWSM, WFE, PP120, with magnitudes of 0.65, 0.20, 0.25, respectively, but negatively correlated with EN120D (-0.32). Genetic correlation (rG) between EN90D and EM90D was 0.18 and 0.19 between EN120D and EM120D. The estimates of rG among EN90D & PP90D and EN120D & PP120D were -0.99 and -0.99, respectively.
3. The ranges in BLUP for most egg production and partial egg recording traits were moderate or high in all generations; the ranges in the control, 1st, 2nd, and 3rd generations being 5.8, 5.8, 5.5 and 5.5 days for ASM, 317, 337, 360 and 345 g for BWSM, 4.7, 4.1, 4.7 and 1.45 g for WFE, 26, 25, 26 and 24 egg for EN90D, 702, 700, 740 and 745 g for EM90D, 25, 27, 25 and 25 egg for EN120D and 744, 740, 765 and 765 g for EM120D, respectively.
4. The three generations of selection were superior in most egg production and partial egg recoding traits than the base generation (P |
