Oestrus and pregnancy diagnosis by milk progesterone assay in the mare.

This research focused on monitoring the daily milk progesterone levels in four mares for several weeks after giving birth. The study found that progesterone levels fluctuated, peaking rapidly during the luteal phase then decreasing unless the mare was pregnant, in which case they remained high. This technique could be used to detect silent heat and ovarian dysfunction in mares.

Study Design and Methodology

• The research focused on four mare subjects, analyzing their milk progesterone profiles daily for a period of four to five weeks after they had foaled.
• Progesterone levels in the mares’ milk were determined through direct radioimmunoassay, a scientific method that utilizes iodinated progesterone as a labelled antigen to detect and measure concetration of progesterone hormone.

Findings and Observations

• In the first 10 days after foaling, the researchers noted that the concentration of milk progesterone in mares varied between 1 to 5 nmol/1 (0·3 to 1·6 μg/1).
• The study shows that the first ovulation usually took place around the tenth day after childbirth.
• Progesterone levels rose significantly during the luteal phase, reaching a peak level of 30 to 45 nmol/1 (9·4 to 14·2 μg/1) within five to 10 days.
• Unless the mare became pregnant, the progesterone levels dropped to lower concentrations. If the mare was pregnant, the progesterone levels remained high.

Practical Implications

• The research presents potential insights into the use of milk progesterone assays for determining silent heat and diagnosing ovarian dysfunctions in mares.
• “Silent heat” refers to the absence of detectable signs of estrus or “heat” in mares even though they are ovulating. On the other hand, ovarian dysfunction refers to any disorder or irregularity in the normal functioning of the ovaries.
• Through monitoring progesterone levels, indications of these conditions can potentially be spotted and addressed.