Effects of Six-Hour Pre-Incubation Thermal Conditioning and Prolonged Storage on Egg Quality, Embryogenesis, Hatchability, and Post-Hatch Physiology of Plymouth Rock Hybrid Chickens in Tropical Climate of Ghana

Prolonged storage negatively impacts incubation outcomes in commercial hatchery operations, highlighting the need for efficient storage strategies. This study assessed the impact of prolonged storage durations and six-hour pre-incubation thermal conditioning (PTC) on egg quality, embryonic development, hatchability, chick quality, blood profile, and thermoregulation. A total of 2,000 fertile eggs were collected from a flock of 72-week-old Plymouth Rock hybrid hens and subjected to a 2 × 2 factorial design, involving storage for either 14 or 21 days, with or without the application of 6-hour PTC. Following storage, the eggs were incubated in a Jamesway P5000 set at a temperature of 37.5°C and relative humidity of 56%, then transferred on incubation day 18 to a hatcher set at 36.5°C and 60% until hatching. Results revealed that prolonged egg storage without PTC significantly diminished egg protein while PTC effectively countered this decline, enhancing Haugh unit values and blastoderm diameter. Prolonged egg storage without PTC also resulted in increased relative egg weight loss (REWL), fluctuated daily eggshell temperature, and reduced embryonic growth during incubation while PTC significantly reduced these effects, with embryos demonstrating significantly enhanced growth. Additionally, while fertility rates remained stable across all treatments, PTC significantly reduced mortality and improved hatchability by 11.4% in 14-day stored eggs and 10.8% in 21-day stored eggs. It also shortened incubation time, increased post-hatch chick body weights and enhanced their hematological and serum profiles, including normalized thyroid hormone (T3 and T4) levels compared to the non-PTC (control) group. Pearson correlation showed that longer incubation time was positively correlated with higher rectal temperature, serum glucose, and thyroid hormones, but negatively correlated with hemoglobin, mean corpuscular hemoglobin, and total protein in non-PTC chicks. In conclusion, six-hour pre-incubation thermal conditioning mitigates the negative effects of prolonged egg storage and enhances embryogenesis, hatchability, chick quality, blood profile, and thermoregulation in Plymouth Rock hybrid chickens. Keywords: Embryonic development, Extended egg storage, Plymouth rock hybrid chicken, Pre-incubation thermal conditioning, Thermoregulation