Repeatability of Production Traits of Sepahan Native Chickens in Diets Including Camelina and Soybean Oil

Introduction
Native chickens are valuable genetic resources in Iran, having evolved through natural selection and adaptation to local environmental conditions. They represent a national asset and contribute to rural livelihoods and food security. The growing global population, economic development, increased life expectancy, and adoption of dietary habits from developed countries have led to higher demand for animal-based protein. Iranian native breeds, such as the Sepahan chicken, are genetically diverse and adaptable to local climates. moderate disease resistance, and acceptable product quality, making them valuable for breeding and research programs. Previous studies on Sepahan hens in rural conditions showed that these birds produce an average of approximately 155 eggs per year, with a mean weight of 53 g and a hen-day production rate of around 44%. Their performance is highly influenced by environmental and management factors, with warmer climates reducing the onset of lay and colder climates increasing egg weight. However, the overall production and feed efficiency remain lower than commercial lines. Improving these traits through nutritional management and selective breeding is a priority in semi-intensive and rural production systems. Recent research highlights the potential of omega-3-rich oils, such as Camelina oil, and phytogenic additives, including cinnamon and lemon balm essential oils, to enhance poultry health and product quality. although several studies have examined the effects of dietary energy, protein, amino acids, and mineral levels on native chicken performance, there is limited information on the variance components and repeatability of production traits under such nutritional interventions. Estimating repeatability at the experimental unit level, even without pedigree data, allows assessment of performance stability and aids the design of management and selection strategies. Therefore, the objective of this study was to evaluate the effect of dietary oil (soybean vs. Camelina) on egg production, egg mass, and feed conversion ratio (FCR) in Sepahan native hens, and to estimate variance components and repeatability for these traits at the pen level. The findings provide insights into production performance and the potential for nutritional and genetic improvement in this native breed.
Method
The study involved 864 Sepahan hens aged 54–62 weeks, housed in floor pens with a temperature of approximately 20°C, a 16-hour light/8-hour dark photoperiod, and a stocking density of 500 cm² per bird. Beforeto the experimental period, hens were adapted to the experimental conditions for two weeks. A completely randomized design with two dietary treatments (soybean oil and Camelina oil) was employed. Each treatment included six replicates, with eight hens per pen, for a total of 12 experimental units (pens). Diets were formulated using WUFFDA software to meet the nutritional requirements of native hens, differed only in oil source. Feed was provided as mash, and water and feed were offered ad libitum throughout the eight-weeks study. Daily records of egg production and egg weight were collected at the pen level. Weekly calculations included hen-day egg production (%), average egg weight, egg mass (g/hen/day), and FCR (feed intake per unit egg mass). Variance components and repeatability were estimated using a mixed-effects model with pen as a random effect and dietary oil as a fixed effect, modeling weekly records as repeated measures. Between-pen (σ²ᵤ) and within-pen (σ²ₑ) variance components were estimated using restricted maximum likelihood (REML) in SAS 9.1, and repeatability (R) was calculated as σ²ᵤ / (σ²ᵤ + σ²ₑ). Duncan's multiple range tests at P < 0.05 were used to compare mean differences between treatments.
Results
The effects of dietary oil on egg production, egg mass, egg weight, feed intake, and feed conversion ratio (FCR) in Sepahan native hens are different. Mean egg weight in the soybean oil group was 52.1 ± 1.9 g, while the Camelina oil group exhibited a slightly higher mean of 53.2 ± 2.0 g. Feed intake averaged 251 ± 13 g/hen/day in the soybean group and 256 ± 16 g/hen/day in the Camelina group. Statistical analysis indicated that these differences were not significant (P>0.05), suggesting that replacing soybean oil with Camelina oil did not influence either egg weight or feed consumption. in contrast, dietary oil source significantly affected egg production, egg mass, and FCR. Hens fed Camelina oil produced 39.2% of hen-day eggs compared to 35.8% in the soybean group, representing a significant improvement (P<0.05). Egg mass also increased significantly from 15.9 g/hen/day in the soybean group to 17.7 g/hen/day in the Camelina group (P<0.05). This improvement in production efficiency was accompanied by a reduction in FCR, which decreased from 3.22 to 2.98 kg feed per kilogram of egg mass (P<0.05), indicating enhanced feed utilization. Variance component analysis revealed that approximately 38% of the observed variation in egg production and egg mass was attributable to consistent differences between experimental units (pens), with the remainder due to within-pen weekly fluctuations and random effects. In contrast, FCR exhibited greater within-pen variability, resulting in a lower repeatability of 0.30. These results suggest that while egg production and egg mass are relatively stable traits over time, FCR is more sensitive to short-term environmental and management changes. Overall, these findings demonstrate that dietary supplementation with Camelina oil enhances production performance and feed efficiency in Sepahan native hens. The improvement occurs without affecting feed intake or egg weight, highlighting the potential of Camelina oil as a nutritionally and economically valuable dietary modification in native poultry production systems.
Conclusions
Camelina oil improved egg production and egg mass and enhanced feed efficiency, consistent with studies on omega-3-enriched diets in laying hens. While production levels in Sepahan hens were lower than those of commercial lines, the relative response demonstrates nutritional potential. The range of production traits (egg production: 28–46%, egg mass: 11.5–21 g/day, FCR: 2.60–3.80 kg/kg) aligns with reports from other native chicken populations and indicates variability among pens. Moderate repeatability of egg production and egg mass supports the use of repeated pen-level measurements for identifying superior units for management or selection. Lower repeatability of FCR highlights its susceptibility to environmental and management factors and suggests the need for more extended observation periods or additional replicates to assess feed efficiency accurately. Dietary inclusion of Camelina oil enhanced egg production, egg mass, and feed efficiency in Sepahan native hens. Moderate repeatability of production traits indicates reliable performance assessment at the pen level. Nutritional strategies such as replacing soybean oil with Camelina oil can improve production in native chickens, contributing to higher economic returns in rural poultry systems. Future studies should estimate genetic parameters using pedigree-based models and investigate egg quality traits and metabolic indicators in conjunction with production traits to optimize breeding strategies.