Recipient Organization
Agricultural Research Service
600 E. Mermaid Lane Rm 2023
Glenside,PA 19038-8551
Performing Department
(N/A)
Non Technical Summary
Meat production is the primary goal of the turkey industry. Selection for growth production has negatively impacted the reproductive performance of breeding hens. The number of eggs laid per hen greatly impacts the number of young turkeys (poults) that can be reared for meat production. Low egg producing hens cost the industry roughly $50 million a year in lost poult production (250 million turkeys/year at $1-$2 per fertile turkey egg). Increasing the number of eggs low egg producing hens lay in a given cycle would be beneficial to the turkey industry, though the biological mechanisms leading to lowered egg production are not well characterized. Egg production is governed by the reproductive axis but other neuroendocrine axes can influence the activity of the reproductive axis. Our previous research associated increased thyroid axis activity with the low egg production phenotype, leading to the hypothesis that hen egg production rates are regulated by thyroid hormones. The current proposal aims to define the regulatory role of thyroid hormone in the control of egg production rates in turkey hens. Our specific objectives are to: 1) Define the hormonal profiles of the reproductive and thyroid axes in low egg producing turkey hens (LEPH), averageegg producing turkey hens (AEPH), and highegg producing turkey hens (HEPH) during the open period; 2) Determine the influence of circulating thyroid hormone levels on the reproductive axis during peak egg production; and 3) Characterize pituitary responsiveness to thyroid axis stimulation in LEPH and HEPH. Taken together these specific objectives will interrogate the relationship between the thyroid and reproductive axes and the implication of this relationship in observed hen egg production rates. Completion of this research will provide the poultry industry with biomarkers indicative of egg production rates that can be used in breeding programs to increase hen reproductive performance, ultimately increasing the number of poults produced per hen. Improvements to hen reproductive performance will increase the efficiency of the poultry industry, underpinning meat production for the growing human population.
Animal Health Component
20%
Research Effort Categories
Basic
80%
Applied
20%
Developmental
0%
Goals / Objectives
The goal of this research is to definethyroid axis activity in the context of the preovulatory hormonal surge, linking thyroid axis pertubationsto the low egg production phenotype in turkey hens. Our specific objectives are to: 1) Define the hormonal profiles of the reproductive and thyroid axes in low egg producing turkey hens (LEPH), averageegg producing turkey hens (AEPH), and highegg producing turkey hens (HEPH) during the open period; 2) Determine the influence of circulating thyroid hormone levels on the reproductive axis during peak egg production; and 3) Characterize pituitary responsiveness to thyrotropin-releasing hormone (TRH) stimulation in LEPH and HEPH.
Project Methods
Radioimmunoassays will be used to quantify circulating plasma progesterone, estradiol, triiodothyronine, and thyroxine concentrations in low, average, and high egg producing turkey hens on an hourly basis throughout the open period for the preovulatory hormonal surge. Feed inclusion of synthetic thyroid hormone (thyroxine (T4)1 ppm) or a thyroid hormone synthesis inhibitor (propylthiouracil (PTU), 0.1%) for a period of two weeks will be used to alter circulating thyroid hormone levels in average egg producing hens. Levels of mRNA will be determined for key genes of the thyroid and reproductive axes using real-time quantitative PCR (RT-qPCR). Injections of thyrotropin releasing hormone (TRH, 0.25 ug/kg) will be administered to low and high egg producing hens. Pituitary gene expression related to the thyroid and reproductive axes will be determined using RT-qPCR and circulating thyroid and steroid hormones will be determined using radioimmunoassays.