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. 2025 Jun 20;104(9):105459. doi: 10.1016/j.psj.2025.105459

Genetic analysis of egg production traits in four chicken breeds using a full diallel cross

Philimon Teshome a,b,c,⁎, Gebeyehu Goshu b, Wondmeneh Esatu c, Tadelle Dessie c
PMCID: PMC12266366  PMID: 40592295

Abstract

In the present study, effects of crossbreeding on egg production traits were evaluated using a 4 × 4 full diallel cross involving four chicken breeds: Improved Horro (H), Sasso (S), Potchefstroom Koekoek (K), and Dz-white feathered (D). The experiment included 800 chickens in a completely randomized design. Data on egg production traits were collected over 40 weeks (WK). Genotypes exhibited significant variations (P < 0.0001) in age at first egg (AFE), body weight at sexual maturity (BWSM), egg weight at first egg (EWAFE), egg number (EN), hen-housed egg production (HHEP), hen-day egg production (HDEP), and egg mass (EM). Heterosis effects (He) varied widely, with positive He for BWSM and EM in most crosses, while AFE consistently showed negative He. All reciprocal crosses showed positive He for EWAFE, while direct crosses had negative values except H × S and H × D. The K × H cross showed the highest He for HHEP (26.85 %), HDEP (29.44 %), EM (40.88 %), and EN (28.27 %). The cross D × H also exhibited strong He for HHEP (25.16 %) and EN (24.60 %), while K × S ranked second for HDEP (22.60 %) and EM (33.89 %). Reciprocal crosses showed positive He for BWSM, EWAFE, HHEP, HDEP, EM, and EN, except AFE. General combining ability (GCA) and specific combining ability (SCA) effects were highly significant (P < 0.0001) for all traits. Reciprocal effects (RE) and maternal effects (Me) also influenced trait expression. GCA/SCA ratios indicated that non-additive effects influenced AFE, while additive effects influenced EWAFE. Moderate ratios for HHEP, HDEP, EM, and EN suggested a balance between additive and non-additive effects. Optimizing crossbreeding strategies, aligning with synthetic breed development, using a K sire with H and S dams, and a D sire with H dam, is recommended to improve egg production.

Keywords: Combining ability, Egg production traits, Heterosis, Maternal effects, Reciprocal effect

Introduction

In Ethiopia, chicken production is deeply integrated into the livelihoods of smallholder farmers, contributing to household income and food security by providing meat and eggs (Mengesha et al., 2022). Eggs are a vital source of high-quality protein, essential vitamins, and minerals, particularly in developing countries like Ethiopia (Shumuye et al., 2018; Passarelli et al., 2022). However, despite the importance of eggs, the country’s egg production remains far below its potential, with low productivity and poor egg quality being major constraints (Kassa et al., 2021; Alebachew et al., 2022). The current gaps in egg production in Ethiopia are multifaceted. Indigenous chicken breeds, which constitute the majority of the poultry population, are well-adapted to local environments but exhibit low egg production rates, small egg size, and inconsistent laying patterns (Mengesha et al., 2022; Damte et al., 2024). On the other hand, exotic and synthetic breeds, while having higher productivity, often struggle with adaptability to local conditions, disease resistance, and feed efficiency (Sebho, 2016; Assefa et al., 2023). This disparity highlights the need for innovative breeding strategies that combine indigenous breeds' adaptability and resilience with the high productivity of exotic and synthetic breeds. Crossbreeding has been identified as a promising approach to address these challenges (Mokoena et al., 2024), but there is limited research on the optimal crossbreeding combinations and their long-term impacts on egg production traits in the Ethiopian context.

To address these gaps, this study focuses on estimating crossbreeding parameters for egg production traits by crossing four distinct chicken populations: one locally improved breed (H), two exotic breeds (S and K), and one synthetic breed (D), in a 4 × 4 full diallel mating. The diallel cross design is a powerful tool for evaluating the genetic architecture of quantitative traits, such as growth rate, egg production, and feed efficiency. By estimating general combining ability (GCA) and specific combining ability (SCA), this approach partitions genetic variance into additive and non-additive effects, providing insights into the breeding value of parental lines and the heterotic potential of their crossbred offspring (Wearden et al., 1965). Additionally, the design allows estimation of heritability for complex quantitative traits, which is critical for predicting selection response. In this study, we apply this framework to assess the genetic potential of parental breeds and their crosses for egg production, aligning with our goal of developing synthetic chicken breeds that enhance the productivity and resilience of poultry farming in Ethiopia.

Materials and methods

Study Area

This study was conducted at the poultry farm of Werer Agricultural Research Center, in the Afar Regional State of Ethiopia, located 280 km from the capital Addis Ababa, at an altitude of 750 meters above sea level (Jemal et al., 2019). The mean annual rainfall is less than 590 mm, with May and June being the driest months. The highest raining season accounts for 60 % of the yearly total rainfall from July to September, whereas March and April contribute 20 % of the annual rainfall. The area is characterized by high temperatures ranging from 19.3°C to 45°C (Atsbaha et al., 2022).

Description of experimental birds

For this study, a 4 × 4 full diallel cross involving Improved Horro (H), commercial Sasso (S), Potchefstroom Koekoek (K), and Dz-white feathered (D) chickens was used. All four breeds used in the present study were previously introduced in the study area (Afar Regional State) for adaptation and crossbreeding works by Werer Agricultural Research Center and the Regional Research Institute starting from 2013/14. The Horro is an indigenous Ethiopian chicken breed enhanced through selective breeding, transitioning into a dual-purpose breed. By the 7th generation at Debre Zeit Agricultural Research Center (DzARC), it achieved 171 eggs/year (Wondmeneh, 2015). The present study used 16th generation Horro chickens. The Dz-White, a synthetic white-feathered breed developed at DzARC, was derived from Lohmann Silver, Potchefstroom Koekoek, and local white ecotypes (Samrawit et al., 2020), with birds from the 13th generation used in this study. The Potchefstroom Koekoek, a South African composite breed (White Leghorn × Black Australorp × Barred Plymouth Rock), is known for its black-and-white barred plumage and sex-linked color differentiation (Grobbelaar et al., 2010). In Ethiopia, it produces 200 eggs/hen/year, with males weighing 2.65 kg and females 1.87 kg (Wondmeneh et al., 2011). The Sasso, a hardy French dual-purpose breed, excels in smallholder systems, laying up to 229 eggs/year under village conditions (Aman et al., 2017). Introduced in Ethiopia by the Ethio-Chicken private farm, it demonstrates strong adaptability (Guni et al., 2021).

Breeding plan and bird management

Crossbred offsprings were produced through random mating, with a balanced sex ratio of 1:5 (male to female) maintained across all breeding groups. For Horro dams, due to their small size, artificial insemination was used by collecting semen from sires of S, K, and D chicken breeds. Semen collection was performed in the afternoon through the abdominal massage technique (Bakst and Dymo, 2013). The freshly pooled semen was then diluted with a 0.9 % saline solution at a ratio of 1:3. For insemination, 0.1 ml of the diluted semen was deposited into the left oviduct of the hens twice a week using a pipette. Fertile eggs were collected, cleaned, and recorded daily according to breeds and crossbreds. Following a seven-day collection period, eggs that were uniformly sized, properly shaped, and free of shell defects were placed in an incubator under standard conditions (37.5°C and 55 % relative humidity). On the 18th day of incubation, the eggs were candled to distinguish fertile eggs from those with dead embryos. Only eggs with viable embryos were moved to the hatchery (maintained at 36.5°C and 75 % humidity), where each hatching tray was labeled according to their breed categories for tracking. Hatchability was assessed on day 22 of incubation. Accordingly, from the diallel cross, 4 purebreds (H, S, K, D), 6 crossbred (H × S, H × K, H × D, S × K, S × D, K × D), and six reciprocal crossbred (S × H, K × H, D × H, K × S, D × S, D × K) progenies were obtained. From purebreds and crossbreds of each genotype, a total of 800 hens (Table 1) were randomly distributed into 48 pens (16 progenies by 3 replications) under a completely randomized design (CRD).

Table 1.

Least square means (±SE) for AFE, BWSM, and EWAFE.

Genotypes HH (n) HD (n) AFE (days) BWSM (g) EWAFE (g)
Purebred
H 40 39 157.03a±1.75 1369.78h±17.90 32.23i±0.50
S 60 56 153.70ab±1.48 1779.50d±8.95 39.10cd±0.41
K 50 50 151.43bc±0.69 1683.56fg±5.61 37.52e±0.64
D 60 60 150.93bc±2.11 1669.56fg±7.00 35.04fg±0.08
Crosses
H × S 50 49 151.47bc±0.68 1758.00d±27.70 36.16f±0.21
H × K 60 60 145.10d-g ± 2.51 1757.67d±2.17 34.14gh±0.24
H × D 45 44 148.10cde±1.13 1644.89g±20.60 33.67h±0.24
S × K 55 54 150.40bc±136 1953.78b±22.10 38.14de±0.04
S × D 45 43 150.03bc±0.18 1858.67c±10.70 36.18f±0.52
K × D 45 45 143.47fgh±0.48 1687.11fg±17.00 36.09f±0.12
RE
S × H 45 44 148.93bcd±1.33 1740.89de±16.10 39.55bc±0.09
K × H 60 60 140.13h±1.14 1778.44d±10.40 38.18de±0.37
D × H 50 50 144.13e-h ± 1.60 1678.22fg±2.47 37.33e±0.67
K × S 45 43 149.27bcd±1.02 2032.22a±12.10 41.14a±0.65
D × S 45 44 147.27c-f ± 2.29 1884.00c±28.60 40.72ab±0.38
D × K 45 45 142.37gh±1.23 1701.11ef±21.20 39.92bc±0.16
P-value <0.0001 <0.0001 <0.0001
CV 1.67 1.68 1.84
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a-iMeans with the same letter in a column are not significantly different (P < 0.05); H, Improved Horro; S, Commercial Sasso; K, Potchefstroom Koekoek; D, Dz-white; HH, hen-housed; HD, hen-day; Males are listed first in the cross.

All experimental chickens were vaccinated against Newcastle disease (HB1 and Lasota), Gumboro (Infectious Bursal disease), fowl typhoid, and fowl pox based on the producer’s manual. Starting from hatch chickens were provided with a starter ration (20 % CP and 3000 kcal/kg ME) until 8 WK of age, followed by grower ration (18 % CP and 2950 kcal/kg of ME) from 9 to 20 WK, and then the ration was changed into layer ration (16 % CP and 2800 kcal/kg of ME) from 21 to 40 WK. Clean water was always available in a drinker. During the brooding and growing phase (hatch to WK 8), fluorescent lamps provided artificial lighting. The photoperiod was set at 16–18 hours of light (20–40 lux) for the first 5 days. Thereafter, it was reduced to 16 hours of light (5–10 lux) until WK 8, following standard management practices for dual-purpose chickens.

Studied traits and data measurements

The four purebred and twelve F1 crossbred chickens obtained from the diallel crosses were evaluated for Age at first egg (AFE), body weight at sexual maturity (BWSM), egg weight at first egg (EWAFE), total egg numbers (EN), hen-housed egg production (HHEP), hen-day egg production (HDEP), and egg mass (EM). Data for AFE, BWSM, EN, EWAFE, EM, and egg production were collected from 800 hens. AFE was calculated from the hatching date of the hen to the production of the first egg laid by the flocks. BWSM was measured as the weight of hens in the group at AFE. To determine EN, eggs laid were collected twice a day (morning and afternoon) from the start of lay up to 40 WK of age, and the number of eggs was recorded. The average weight of the first ten eggs laid consecutively in each pen was recorded to determine EWAFE (Fikrineh et al., 2023). HHEP was calculated as the total number of eggs produced by the hens, divided by the number of hens initially housed and the number of days that the birds were inlay, while HDEP was calculated as the total number of eggs produced by the hens, divided by the number of hens alive at the time of egg collection (Hunton, 1995). EM was determined as the product of EN per hen and average egg weight.

Statistical analysis

Egg production data were analyzed for variation between the genotypes using the general linear model procedure of R (Version 4.4.2) (R Core Team, 2023). Differences considered to be significant (P < 0.05) were compared by Duncan’s Multiple Range Test (Duncan, 1955).

Genetic parameters estimation

Diallel analysis was carried out only when the differences among the genotypes were significant. Fixed-effect model of (Griffing, 1956) Model 1, Method 1, a commonly used approach for assessing the genetic potential of breeding lines, especially in diallel crossing experiments, was used. The mathematical model used for the combining ability analysis was:

Yij=μ+Gi+Gj+Sij+rij+eij

Where, Yij = the observed performance of the ith genotype crossed with the jth genotype, μ = the overall mean of the population, Gi and Gj = general combining abilities of the ith and jth genotypes (represents the additive genetic effect of genotype i and j), Sij = specific combining ability for the ith and jth cross (represents the non-additive genetic interaction between i and j genotypes), rij= is the reciprocal effect involving the reciprocal crosses between the ith and jth parents, and eij = random error term, which accounts for any variation not explained by the fixed effects.

Heterosis was calculated on percentage of mid-parents by application of the following formula: H% = {F1 – [(P1 + P2)/2)] / [(P1 + P2) /2] * 100} using mean, where, F1 = the first filial and P1 and P2 are parents in diallel and reciprocal crosses (Williams et al., 2002). Maternal effects for egg production traits were estimated using a set of linear contrasts of the genetic group means (Dickerson, 1969) as follows: Maternal Additive Effect: ½ [(A × B) - (B × A)]

Ethics approval

The protocol for the conduct of animal experiment was approved by the animal research ethical review committee of Collage of Veterinary Medicine and Agriculture of Addis Ababa University under the certificate reference number VM/ERC/01/06/15/2024.

Results

Egg production performance

The least square means for AFE, BWSM, and EWAFE across various genetic groups are detailed in Table 1. Significant differences (P < 0.0001) were observed among all genetic groups. The K × H crossbred had the earliest AFE (140.13 days), while among purebreds, D (150.93 days) matured earliest. K × S crossbreds had the highest BWSM (2032.22 g), and H purebreds the lowest (1369.78 g). For EWAFE, K × S laid the heaviest eggs (41.14 g), while H × D laid the smallest (33.67 g). The performance of genotypes was also assessed for EN, HHEP, HDEP, and EM. Table 2 highlights significant differences (P < 0.0001) for all traits among all genetic groups. K × H and K × S had the highest EN and egg production rates, while S × D and H × D performed the poorest. K × S, K × H, and D × K had the highest EM, with H showing the lowest performance.

Table 2.

Least square means (±SE) for total EN, HHEP, HDEP, and EM.

Genotypes Total EN per hen (n)
 Egg production (%)
 EM per hen (g)
Hen housed Hen day HHEP HDEP
Purebred
H 47.64k±1.85 48.71h±1.15 35.90i±1.16 36.70e±0.54 2048.95j±37.50
S 55.32j±0.59 59.32fg±1.61 41.53h±1.15 44.54d±1.67 2876.02ghi±70.70
K 66.57e±0.04 66.57de±0.04 51.10d±0.69 51.10c±0.69 3335.67ef±32.10
D 60.43g±0.36 60.43fg±0.36 46.26e±0.65 46.26d±0.65 2848.24ghi±27.20
Crosses
H × S 59.30gh±0.43 60.33fg±0.79 44.14efg±0.23 44.92d±0.80 2963.18gh±7.84
H × K 59.55gh±1.18 59.55fg±1.18 43.78fgh±0.60 43.78d±0.60 3000.53g±43.60
H × D 56.44ij±0.31 57.80g±1.61 42.98gh±0.41 44.03d±1.45 2758.50i±86.00
S × K 59.01gh±0.41 60.03fg±0.66 45.63ef±0.43 46.44d±1.01 3208.97f±29.80
S × D 57.78hi±0.28 60.52fg±1.09 43.12gh±0.27 45.16d±0.84 2996.35g±45.40
K × D 71.24bc±0.70 71.24bc±0.70 53.85bc±0.82 53.85bc±0.82 3404.05de±55.80
RE
S × H 60.29g±0.75 61.70f±1.01 44.88efg±0.45 45.93d±0.76 2796.89hi±92.10
K × H 73.93a±0.36 73.93ab±0.36 55.18ab±0.42 55.18b±0.42 3792.82b±39.60
D × H 68.03de±0.50 68.03cde±0.50 51.42d±0.63 51.42c±0.63 3246.25ef±37.10
K × S 72.04ab±0.31 75.48a±1.77 56.78a±1.16 59.45a±0.94 4158.47a±92.20
D × S 64.04f±0.27 65.56e±1.26 50.09d±1.24 51.26c±1.21 3556.08cd±78.30
D × K 69.62cd±0.49 69.62cd±0.49 52.49cd±0.71 52.49bc±0.71 3708.55bc±50.80
P-value <0.0001 <0.0001 <0.0001 <0.0001 <0.0001
CV 1.94 2.91 2.81 3.39 3.21
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a-kMeans with the same letter in a column are not significantly different (P < 0.05); H, Improved Horro; S, Commercial Sasso; K, Potchefstroom Koekoek; D, Dz-white; Males are listed first in the cross.

Heterosis Effect (He)

The heterosis effect (He) on egg production traits was analyzed, with heterosis (%) calculated based on mid-parent values (Table 3). Positive He was observed for BWSM and EM in crosses like H × S, H × K, H × D, S × K, S × D, and K × D, with heterosis ranging from 0.63 % to 20 %. Conversely, AFE showed negative He across all crosses, while EWAFE had negative He except for H × S (1.39 %) and H × D (0.11 %). HHEP, HDEP, and EN mostly exhibited positive He, except for S × K and S × D, which showed negative values. Reciprocal crosses demonstrated positive He for BWSM, EWAFE, HHEP, HDEP, EM, and EN (1.46 % to 40.88 %), while AFE remained the sole trait with a negative He across all genetic groups.

Table 3.

Estimation of heterosis percentage for egg production traits.

Genotypes Traits
AFE BWSM EWAFE HHEP HDEP EM EN
Crosses
H × S −2.51 11.64 1.39 14.02 7.04 20.33 11.69
H × K −5.92 15.13 −2.09 0.65 2.71 11.45 3.31
H × D −3.82 8.24 0.11 4.63 6.13 12.66 5.92
S × K −1.42 12.84 −0.44 −1.47 2.52 3.32 −4.63
S × D −1.50 7.78 −2.40 −1.77 −0.52 4.69 1.06
K × D −5.10 0.63 −0.52 10.62 13.60 10.09 12.19
Reciprocals
S × H −4.14 10.56 10.89 15.92 13.07 13.58 14.22
K × H −9.14 16.49 9.47 26.85 29.44 40.88 28.27
D × H −6.40 10.43 10.99 25.16 17.20 32.58 24.6
K × S −2.16 17.37 7.38 22.60 26.37 33.89 19.90
D × S −3.32 9.25 9.85 14.12 13.65 24.25 9.48
D × K −5.83 1.46 10.03 7.82 10.72 19.94 9.64
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H, Improved Horro; S, Commercial Sasso; K, Potchefstroom Koekoek; D, Dz-white; Males are listed first in the cross.

Combining ability and reciprocal effects

Genetic estimates for general combining ability (GCA), specific combining ability (SCA), and reciprocal effects (RE) for egg production traits are detailed in Table 4. For all the traits studied GCA effects were highly significant (P < 0.0001) across all genotypes. The K breed showed the highest positive GCA values for most traits, except AFE, while the S breed had moderately positive GCA values, except for HHEP, HDEP, and EN. The D breed displayed moderate positive GCA values, excluding AFE, BWSM, and EWAFE, and the H breed had predominantly negative GCA values, except for AFE.

Table 4.

Estimates (±SE) of combining ability and reciprocal effects for egg production traits.

Genotype Egg production traits
AFE BWSM EWAFE HHEP HDEP EM EN
GCA <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001
gH 0.63ab±1.68 −111.38g±6.61 −1.76f±0.35 −3.17h±0.58 −3.45de±0.28 −336.71f±19.47 −3.83e±0.22
gS 2.24ab±0.84 99.73ab±4.67 1.57abc±0.18 −1.48gh±0.50 −0.50cd±0.14 10.28e±9.73 −0.89de±0.11
gK −1.66abc±1.68 36.09cd±6.61 0.64b-e ± 0.35 3.79abc±0.58 3.39b±0.28 324.37ab±19.47 4.20bc±0.22
gD −1.21abc±0.51 −24.45ef±2.02 −0.44e±0.11 0.86efg±0.18 0.56bc±0.09 2.06e±5.96 0.53d±0.07
SCA <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001
sH×S −1.03abc±1.45 12.50cde±5.72 0.85b-e ± 0.30 1.72c-f ± 0.50 1.09bc±0.24 37.75e±16.86 2.06bcd±0.19
sH×K −4.71c±1.87 94.75ab±7.39 0.09e±0.39 1.41c-f ± 0.65 1.26bc±0.31 240.29bcd±21.76 2.70bcd±0.25
sH×D −1.98abc±0.84 16.67cde±3.30 1.83ab±0.18 4.22ab±0.29 3.70b±0.14 243.88bcd±9.73 5.11ab±0.11
sS×K −0.57abc±1.19 39.22cd±4.67 1.50a-d ± 0.25 5.57a±0.41 6.50a±0.20 474.75a±13.76 7.72a±0.16
sS×D −1.38abc±1.26 12.67cde±4.95 2.27a±0.26 3.49a-d ± 0.43 3.05b±0.21 279.87bc±14.60 2.52bcd±0.17
sK×D −0.55 abc±1.45 7.00cde±5.72 1.92ab±0.30 −0.68fg±0.50 −0.68cd±0.24 152.25b-e ± 16.86 −0.81de±0.19
RE NS <0.0401 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001
rS×H 1.27ab±0.94 8.569cde±3.6 −1.70f±0.20 −0.38efg±0.32 −0.5cd±0.16 83.15de±10.88 −0.68de±0.12
rK×H 2.48a±1.19 −10.39de±4.67 −2.02f±0.25 −5.70i±0.41 −5.70e±0.20 −396.15f±13.76 −7.19f±0.16
rD×H −1.67abc±1.26 48.80b±4.95 0.51cde±0.26 2.06b-e ± 0.43 2.33bc±0.21 168.31b-e ± 14.60 2.54bcd±0.17
rK×S 0.90ab±0.51 108.59a±2.02 0.24de±0.11 1.45c-f ± 0.18 1.77bc±0.09 180.35b-e ± 5.96 0.77cd±0.07
rD×S −0.74abc±1.19 47.46bc±4.67 0.14e±0.25 −0.22efg±0.41 −0.13c±0.20 95.15cde±13.76 −0.27d±0.16
rD×K −2.57bc±0.94 −66.12fg±3.69 0.62b-e ± 0.20 1.07def±0.32 0.94bc±0.16 61.15de±10.88 2.03bcd±0.12
GCA/SCA 0.100 0.370 1.507 0.670 0.638 0.494 0.447
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a-gMeans with the same letter in a column are not significantly different (P < 0.05); H, Improved Horro; S, Commercial Sasso; K, Potchefstroom Koekoek; D, Dz-white; g, General Combining Ability; s, Specific Combining Ability; r, Reciprocal Effect; Males are listed first in the cross.

Variation due to SCA effects was high (P < 0.0001) for all traits, with positive values observed across genetic groups, except for AFE. The H × K crossbred had the highest SCA for BWSM, followed by S × K, H × D, S × D, and H × S. The S × D crossbreds showed the highest SCA for EWAFE, while S × K had the highest SCA for HHEP, HDEP, EM, and EN. K × D recorded the lowest SCA for BWSM, HHEP, HDEP, and EN.

Reciprocal effects (RE) were significant (P < 0.0001) for EWAFE, HHEP, HDEP, EM, and EN. D × K had the highest positive RE for EWAFE, while D × H showed the highest RE for HHEP and HDEP. K × S had the highest RE for EM, and D × H for EN. Negative RE values were observed for S × H and K × H in EWAFE, and for D × S, S × H, and K × H in EN. The GCA/SCA ratios varied, with EWAFE having the highest ratio (1.51), indicating a stronger GCA influence. HHEP, HDEP, EM, and EN showed moderate ratios, while AFE and BWSM had the lowest.

Maternal Effect (Me)

Table 5 presents estimate of the Me on egg production traits, showing varying magnitudes with both positive and negative values. Most egg production traits had positive Me estimates. The H × S cross combination had a positive Me on AFE, whereas H × K, H × D, S × K, S × D, and K × D displayed negative effects. Positive Me values were observed for BWSM and EM across all cross combinations. For EWAFE, all combinations except H × S showed positive estimates. EN had positive Me for H × K, H × D, S × K, and S × D, but negative for H × S and K × D.

Table 5.

Means ± SE for maternal breed effects (Me) on egg production traits.

Genotypes AFE
 BWSM
 EWAFE
 EM
 EN
Me P-value Me P-value Me P-value Me P-value Me P-value
H × K −2.48±0.00 0.448 10.39±10.09 0.325 2.02±0.39 <0.001 396.1 ± 48.08 <0.001 7.19±0.86 <0.001
H × S 1.27±1.01 0.235 8.44±17.79 0.644 −1.53±0.18 <0.001 83.15±81.97 0.322 −0.68±1.56 0.669
H × D −1.98±0.46 0.001 16.67±19.97 0.421 1.83±0.65 0.017 243.8 ± 47.99 <0.001 5.11±1.02 <0.001
S × K −0.57±1.74 0.751 39.22±9.46 0.002 1.49±0.57 0.025 474.8 ± 54.2 <0.001 7.72±1.36 <0.001
S × D −1.38±1.83 0.467 12.70±15.56 0.432 2.27±0.26 <0.001 279.9 ± 57.1 <0.001 2.52±1.07 0.039
K × D −0.55±1.35 0.692 7.00±30.64 0.823 1.92±0.23 <0.001 152.2 ± 33.8 0.001 −0.81±1.02 0.443
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H, Improved Horro; S, Commercial Sasso; K, Potchefstroom Koekoek; D, Dz-white; Males are listed first in the cross.

Discussion

Egg production performance

AFE is a vital trait in poultry production, influencing economic returns, egg production, and flock management (Liu et al., 2019). Consequently, AFE is a critical indicator of reproductive performance in hens (Tan et al., 2021).

In this study, the K × H crossbred showed the earliest AFE, suggesting that this crossbred combination accelerates sexual maturity compared to both purebreds and other crossbreds, highlighting the presence of hybrid vigor in the K × H cross. Similar results were obtained by Shambel et al. (2022), in which the crossbred K × H reached sexual maturity early compared with other crosses. Among purebreds, the D breed reached sexual maturity earliest, followed by K, S, and H. This indicates that the D and K breeds have genetic traits favoring earlier sexual maturity compared to S and H. AFE for D and K breeds in the current study was higher than the report of Samrawit (2020) and Shambel et al. (2022), respectively. However, Fikrineh et al. (2023), reported high AFE, for K (166.50 days) compared to the present result. The AFE of S breed obtained in the current study was in line with the result reported by Guni et al. (2021). Similar to the current result, Wondmeneh (2015) and Shambel et al. (2022) reported 156.6 days and 156 days AFE for H chicken breed, respectively. In contrast, early AFE for H had been reported by several researchers such as (Kedija et al., 2020; Samrawit, 2020; Shambel and Atsbaha, 2024). However, the present finding for H, was much higher than reported by Nigussie (2011). The K × D crossbred group also showed early maturity, suggesting that the K and D breeds complement each other well in terms of reducing AFE. Reciprocal crosses (e.g., K × H vs. H × K) showed variability, indicating that the maternal or paternal lineage may influence AFE.

In the present study, the higher BWSM was recorded for crossbred chickens. The K × S and S × K crossbreds consistently showed high BWSM, indicating that this combination results in larger birds at sexual maturity. This could be advantageous for meat production or overall robustness. The superiority of crossbreds over purebreds for BWSM has been reported by several researchers, such as Iraqi et al. (2012), Debes (2017), and Bassey et al. (2021). Among purebreds, S had the heaviest BWSM, followed by K, while H had the lowest. Similarly, Osei-Amponsah et al. (2012) reported that Sasso has the heaviest BWSM compared with forest and savannah chicken breeds. In addition, Fikrineh et al. (2023) reported the highest BWSM in their study. On the other hand, studies on crossbreeding indigenous breeds with exotic breeds (Kedija et al., 2020; Shambel et al., 2022) showed that lowest BWSM for H. The D × H and H × D crossbreds had the lowest BWSM, suggesting that the H breed may dilute BW when crossed with D.

Among purebreds, S laid the heaviest eggs, followed by K, D, and H. The increased EWT observed in S chickens could be attributed to the positive correlation between BW and EWT (Du Plessis and Erasmus, 1972). In line with this result, Fikrineh et al. (2023) reported similar EWAFE results for the K breed. The present EWAFE result for the D breed was in line with the findings reported by Habtamu et al. (2023). In contrast, Kedija et al. (2020) reported heavier EWAFE for H compared to the current result. The K × S crossbred group laid the heaviest eggs, indicating that this combination is favorable for producing larger eggs early in the laying cycle. The D × S and D × K crossbreds also performed well in terms of EWAFE, indicating that the use of the D breed contributes positively to egg size when crossed with S or K. In line with the present finding, several studies showed that the crossbreds showed superiority in terms of EWAFE compared to purebreds (Balcha et al., 2021; Wang et al., 2022).

The observed differences in BWSM, EWAFE, and AFE suggest interrelated effects of body weight and sexual maturity in these breeds. For instance, the K × H crossbred, which exhibited the earliest AFE, also had moderate BWSM and EWAFE, implying that early maturation does not necessarily compromise body weight or egg size. Conversely, the S breed and its crosses (e.g., K × S, S × K), which achieved the highest BWSM and EWAFE, tended toward later AFE, aligning with the typical trade-off between growth and reproductive onset. Notably, the D × H and H × D crossbreds, with the lowest BWSM, may reflect a dilution effect of the H breed on weight traits, but their AFE was not the latest, suggesting that genetic factors influencing AFE (e.g., from the D breed) could partially decouple it from BWSM. These patterns highlight the need to consider all three traits jointly in breeding programs, where earlier AFE may favor productivity, while higher BWSM and EWAFE could benefit meat or egg yield depending on production goals.

Among purebreds, K had the highest EN, HHEP, and HDEP, followed by D and S, while H performed the poorest. The EN, HHEP, and HDEP values for K in this study were higher than those reported by Fikrineh et al. (2023). However, Shambel and Atsbaha (2024) reported similar results of HHEP for K, but a higher HHEP value for H. In contrast, Mekete and Ayano (2023) found higher egg production for K compared to the present findings, while their results for the S breed aligned with those of this study. Additionally, under farmer management conditions, Habtamu et al. (2023) reported lower HHEP and HDEP values for the D breed.

K × S and K × H crossbreds recorded the highest EN, HHEP, and HDEP, indicating superior egg-laying performance. This is likely due to heterosis, where the combination of K with H or S results in improved productivity. The EN, HHEP, and HDEP values observed in the present study were slightly higher than the values reported by Shambel et al. (2022) for crossbreds H × K and K × H. In the present study, K × S, K × H, K × D, D × K, D × H, and D × S crossbreds outperformed their purebred counterparts in EN, HHEP, and HDEP. In a crossbreeding experiment involving Fayoumi and Rhode Island Red, Basant et al. (2013) reported that the superiority of crossbreds over their purebred counterparts in HHEP and HDEP. In addition, Emad (2014) also reported high egg production for Sasso and Mandarah crossbred compared with the purebred Sasso. Similarly, Razuki and AL-Shaheen (2011) also reported superiority of crossbreds over purebreds on egg production for crosses involving Iraqi local, White Leghorn, and New Hampshire chicken breeds.

EM is a critical metric for commercial egg production, as it reflects both egg size and laying frequency. K × S, K × H, and D × K crossbreds recorded the highest EM. The same trend was observed by Soliman et al. (2020) when local and commercial strains crossed the crossbreds outperform the local but not the commercial strains. Among purebreds, K and D performed better than S, while H being the least. This reinforces the idea that the K and D breeds are more favorable for egg production traits.

Heterosis Effect (He)

The level of heterosis grows as the genetic distance between parental lines increases, and measuring it is crucial for assessing the enhancement of crossbred characteristics relative to their parents (Mancinelli et al., 2023).

As shown in Table 3 all crosses exhibited negative He for AFE, indicating that crossbred birds achieved sexual maturity earlier than the mid-parent average. This finding aligns with previous research (Hristakieva et al., 2014; Lalev et al., 2014; El-Tahawy and Habashy, 2021; Atsbaha et al., 2023). However, Ni et al. (2023) reported low but positive He for AFE.

BWSM is generally beneficial for dual-purpose breeds, as it can boost both meat and egg production. For egg production, it positively impacts egg weight, overall productivity, and breeding success (Jesuyon, 2024). In this study, all genotypes displayed positive He for BWSM, ranging from 0.63 % to 17.37 %. Crosses involving H, S, D, and K breeds showed promising results for BWSM. Particularly, cross combinations like, K × S, K × H, H × K, S × K, H × S, S × H, D × H, D × S, H × D, and S × D demonstrated high positive He for BWSM. These findings are consistent with previous studies reporting positive hybrid vigor for BWSM (Iraqi, 2008; Assefa et al., 2021; Fikrineh et al., 2023).

While most crosses exhibited negative He for EWAFE, the H × S and H × D crosses showed positive He, suggesting their potential for improving early egg weight. The overall positive He observed in these crosses highlights the significant role of non-additive genetic effects, such as dominance, overdominance, and epistasis, in enhancing these traits.

For HHEP, HDEP, EN, and EM, most crosses displayed positive He. However, specific combinations like S × K and S × D showed negative He for HHEP, HDEP, and EN. Similar results were reported by Saadey et al. (2008) in a 4 × 4 diallel cross involving Fayoumi, Sinai, Rhode Island Red, and White Leghorn breeds, where positive He was observed for egg production and EN. The positive He in most crosses underscores the potential of crossbreeding to enhance egg production.

Combining ability and reciprocal effects

GCA is commonly used in breeding programs to assess the average performance of offspring from a particular individual, indicating the genetic potential passed on by that individual (Julius and Louis, 2019; Temesgen, 2021).

GCA effects were highly significant (P < 0.0001) among purebreds for egg production traits. The variation underscores the importance of additive genetic effects in the inheritance of egg production traits. The K breed showed the highest positive GCA values for HHEP, HDEP, EM, and EN, while S exhibited the highest positive GCA values for AFE, BWSM, and EWAFE. On the other hand, D showed moderate positive GCA values for some traits (HHEP, HDEP, EM, EN) but negative GCA for AFE, BWSM, and EWAFE. This implies that while D may enhance egg production traits, it is less suitable for improving early body weight and egg weight. Notably, the H breed predominantly showed negative GCA values across traits, except for AFE, where it had a positive GCA. Since a positive GCA for AFE reflects a genetic contribution to delayed sexual maturity, H would be unfavorable for breeding programs targeting earlier egg production. For such goals, parents with negative GCA values for AFE would be preferable. Breeds with high additive genetic effects (K and S) should be prioritized as parents in crossbreeding programs, particularly if the long-term goal is to develop a synthetic breed, while also considering heterosis for immediate hybrid vigor in key traits. While its GCA of H chicken breed is generally low, its positive GCA for AFE suggests it could be useful in crosses aimed at reducing the age at sexual maturity.

SCA reflects non-additive genetic effects, such as dominance and epistasis, which are specific to particular breed combinations. High SCA values indicate that certain crosses perform better than expected based on the GCA of the parent breeds. H × K recorded the highest positive SCA for BWSM, indicating strong heterosis for BWSM. This cross also showed moderate SCA for EWAFE, HHEP, HDEP, EM, and EN. S × K showed the highest positive SCA for HHEP, HDEP, EM, and EN, making it a promising combination for improving egg production traits. S × D cross had the highest positive SCA for EWAFE, suggesting that this combination is particularly effective for improving EWAFE. On the other hand, H × D cross showed moderate positive SCA for BWSM, HHEP, and HDEP, indicating potential for improving BWSM and egg production. Crosses with high SCA (e.g., H × K, S × K, S × D) should be prioritized in breeding programs to exploit heterosis and dominance effects. Specific combinations like S × K for egg production and S × D for EWAFE can be used to address specific breeding goals.

The GCA/SCA ratio provides insights into the relative contributions of additive and non-additive genetic effects. Table 4 shows that the GCA/SCA ratios for various traits reveal distinct genetic influences: AFE has a very low ratio, indicating dominance or epistatic interactions are more significant than additive effects, making crossbreeding or selection ideal for improvement. On the other hand, EWAFE has a high ratio, highlighting the dominance of additive effects, making purebred selection highly effective. BWSM, HHEP, and HDEP showed a moderate ratio, with both additive and non-additive effects playing roles, suggesting a combination of purebred selection and crossbreeding. EM and EN also show moderate ratios, with non-additive effects slightly more significant, suggesting hybrid strategies to leverage heterosis alongside purebred selection for optimal results.

Reciprocal effects (RE) reflect the influence of maternal or paternal genetics on trait expression, which can be further modulated by differences in genetic size between parent breeds. The direction of crossing should be carefully considered to optimize outcomes, as larger-bodied breeds often contribute differently to growth, egg production, and resource allocation than smaller breeds.

In this study, RE was significant for all egg production traits except AFE. In line with the present result, Fikrineh et al. (2023) reported significant RE for EN, EM, HHEP, and HDEP. However, the same author reported non-significant RE for BWSM and EWAFE. In contrast to the present findings, Soliman et al. (2020), reported a significant RE for AFE and a non-significant RE for BWSM, EN, and EM.

The crosses D × K and D × H showed the highest positive RE for EWAFE, HHEP, and HDEP, indicating that using D (a moderately larger paternal breed) with K (a moderately larger maternal breed) or H (a small maternal breed) improves EWAFE and egg production efficiency. This may be attributed to the optimal paternal investment from the larger D breed, enhancing nutrient transfer and egg development.

Conversely, the K × S cross had the highest positive RE for EM, suggesting that when K (a moderately large paternal breed) is crossed with S (a large maternal breed), the resulting offspring benefit from improved EM, possibly due to favorable maternal-offspring size compatibility.

However, some crosses (e.g., S × H, K × H) showed negative RE for traits like EWAFE, EM, and EN, implying that the direction of crossing may disrupt optimal genetic size interactions. For instance, if a larger paternal breed (S and K) is paired with a smaller maternal breed (H), maternal resource limitations or developmental mismatches could reduce performance and may not fully exploit heterosis or additive effects.

Thus, breeders should avoid or use caution with crosses exhibiting negative RE, particularly when genetic size disparities may lead to suboptimal maternal effects or developmental trade-offs. Instead, prioritizing crosses where maternal size aligns with paternal contributions (e.g., larger hens for egg production, optimally sized sires for growth) can enhance both additive and non-additive genetic benefits.

Maternal effect (Me)

The Me exhibited variation across most egg production traits, as detailed in Table 5. The H × D cross combination demonstrated a significant Me (−1.98, P = 0.001), indicating that when H (a smaller-sized breed) serves as the sire, it may accelerate sexual maturity compared to reciprocal crosses. However, other crossbred combinations did not show differences. Low and negative estimates for AFE were similarly reported by Lalev et al. (2014) and Kedija et al. (2020).

However, the S × K cross combination displayed a significant Me (39.22, P = 0.002) on BWSM, indicating that S (a larger paternal breed) paired with K (a moderately larger maternal breed) enhances offspring growth, while other interactions were not significant. Consistent with the current findings, Shambel et al. (2022) observed a positive and significant Me on BWSM in H and K crosses. However, the same author reported a positive and significant Me on AFE for the cross combinations, which contrasts with the present results.

Additionally, crossbred combinations H × K, H × D, S × K, S × D, and K × D showed significant Me (P < 0.05) on EWAFE. the H × S combination exhibiting a significant negative Me (−1.53, P < 0.001), implying that the small size of H breeds limits maternal investment in early egg size. In line with the present findings, Iraqi (2008) also reported significant Me on EWAFE.

For EM, the H × K, H × D, S × K, S × D, and K × D cross combinations displayed highly significant Me (P < 0.001), with the strongest effects when larger dams (D, K) were used, whereas the H × S combination was not significant (P = 0.322). The highest estimates of Me on EM observed in this study align with those reported by Kedija et al. (2020), however, unlike the present findings, the effect in their study was not significant. Regarding EN, the H × S and K × D cross combinations were not significant (P > 0.05), while the H × K, H × D, S × K, and S × D combinations showed significant Me (P < 0.05), highlighting the role of maternal body size in sustaining high egg production. Over all, the substantial Me variation underscores the importance of maternal genetic size in egg production traits. Smaller maternal breeds (H) may favor early maturity but limit egg size, whereas larger dams (S, K and D) improve EM and EN, likely due to greater nutrient reserves. Breeders should match maternal size with paternal growth potential to maximize crossbreeding benefits.

In conclusion, the study highlights the importance of additive and non-additive genetic effects in egg production traits. The K × H cross had the earliest AFE, while K × S and S × K showed the highest BWSM and egg weight. K × S and K × H excelled in EN, HHEP, and HDEP. Most crosses displayed positive heterosis, with K having the best GCA for HHEP, HDEP, EM, and EN, and S leading in AFE, BWSM, and EWAFE. The H × K cross showed the highest SCA for BWSM, while S × K performed best for HHEP, HDEP, EM, and EN. D × K and D × H had the highest RE for EWAFE, HHEP, and HDEP, whereas K × S led in EM. However, S × H and K × H had negative RE for EWAFE, EM, and EN. Maternal effects significantly influenced egg production. Based on these results, a synthetic breeding program using K as a sire line and S, and H as dam and D sire with H dam lines is recommended for improved egg production performance.

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Philimon Teshome reports financial support was provided by International Livestock Research Institute. Reports a relationship with that includes:. Has patent pending to. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

Many thanks to the Werer Agricultural Research Center (WARC), for allowing the poultry farm and providing the necessary facilities for this experiment. This work was funded by the International Livestock Research Institute (ILRI), Ethiopia, under the Animal and Human Health Program (grant number: 04/GF/23/6443, January 2023) and partially funded by the Ethiopian Institute of Agricultural Research (EIAR).

Footnotes

Scientific section: Genetics and Genomics

Contributor Information

Philimon Teshome, Email: pteshome@yahoo.com, P.Teshome@cgiar.org.

Gebeyehu Goshu, Email: gebeyehu.goshu@aau.edu.et.

Wondmeneh Esatu, Email: w.esatu@cgiar.org.

Tadelle Dessie, Email: t.dessie@cgiar.org.

Data Availability

Data associated with this article are available from the corresponding author on reasonable request.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

Data associated with this article are available from the corresponding author on reasonable request.

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