Thermal manipulation during mid-embryogenesis alters myogenic gene expression and muscle morphometry in broilers.

Area of Science:

• Poultry Science
• Developmental Biology
• Animal Physiology

Background:

• Embryonic thermal manipulation (TM) is a strategy to improve post-hatch performance in poultry.
• Understanding the effects of different TM protocols on embryonic development and gene expression is crucial for optimizing poultry production.
• Specific gene expression related to muscle development, such as MYOD, and stress response markers like HSP70, are key indicators of TM effects.

Purpose of the Study:

• To evaluate the impact of embryonic thermal manipulation (TM) at varying temperatures (39.5°C and 40.5°C) and durations (6h and 12h daily) on embryonic development.
• To assess the effects of TM on hatchability, embryo mortality, chick quality, yolk sac weight, and breast muscle gene expression (HSP70, MYOD, DIO2).
• To analyze breast muscle histomorphometry and serum hormone levels post-hatch in response to different TM protocols.

Main Methods:

• A total of 4300 Ross 308 hatching eggs were subjected to five treatments: control (37.5°C) and four TM protocols (39.5°C/6h, 39.5°C/12h, 40.5°C/6h, 40.5°C/12h) from day 7 to 16 of embryonic development.
• Parameters evaluated included hatchability, embryo mortality, chick quality scores, yolk sac weight, gene expression (HSP70, MYOD, DIO2) via RT-qPCR, serum hormone levels, and breast muscle histomorphometry.
• Statistical analysis was performed using a completely randomized design to compare treatment effects.

Main Results:

• The 40.5°C/12h TM protocol resulted in significantly lower hatchability (31.55%), reduced chick quality, and increased mid-term and late embryonic mortality.
• Embryonic TM, particularly 40.5°C/12h, led to a higher relative yolk sac weight at hatch and a substantial upregulation of HSP70 gene expression.
• All TM treatments suppressed MYOD expression, while the 39.5°C/6h and 40.5°C/6h protocols increased myocyte area in breast muscle post-hatch compared to control.

Conclusions:

• Embryonic thermal manipulation at 40.5°C, especially for 12 hours daily, negatively impacts hatchability and embryo survival.
• The 39.5°C/6h TM protocol shows promise for enhancing early muscle development by increasing myocyte size and downregulating MYOD expression.
• This specific TM protocol (39.5°C/6h) offers potential benefits for muscle development without compromising hatchability or day-old chick quality.