Oestradiol levels in sheep plasma during the oestrous cycle

Area of Science:

• Reproductive Endocrinology
• Animal Science
• Comparative Physiology

Background:

• Oestradiol is a key hormone regulating the reproductive cycle in ewes.
• Breed-specific variations in reproductive physiology can influence hormone profiles.
• Understanding oestradiol dynamics is crucial for reproductive management in sheep.

Purpose of the Study:

• To quantify and compare oestradiol concentrations in ovarian and peripheral venous plasma across three distinct sheep breeds.
• To investigate potential breed differences in oestradiol secretion during the oestrous cycle.

Main Methods:

• Radioimmunoassay (RIA) was employed to measure oestradiol levels.
• Ovarian venous plasma was collected on Day 9 of the oestrous cycle.
• Jugular venous plasma was collected daily around the period of oestrus.

Main Results:

• Tasmanian Merino ewes exhibited significantly lower mean oestradiol concentrations in ovarian venous plasma compared to Scottish Blackface and Finnish Landrace ewes.
• Mean ovarian venous plasma oestradiol levels were 44.1 pg/ml (Merino), 72.2 pg/ml (Blackface), and 66.8 pg/ml (Finn).
• Peripheral venous plasma oestradiol concentrations were consistently low across breeds (overall mean 1.7 pg/ml), with peak preovulatory values around 3.4-3.9 pg/ml in Finn and Blackface ewes.

Conclusions:

• Significant breed-related differences exist in ovarian oestradiol secretion in ewes.
• Peripheral oestradiol levels are a poor indicator of ovarian oestradiol production, especially outside the preovulatory surge.
• These findings contribute to understanding breed-specific reproductive endocrinology in sheep.