Levels of LH, prolactin and oestrogens in the serum of post-partum mares.

The research investigates the levels of LH (Luteinizing hormone), prolactin, and estrogen in the blood of mares after giving birth, as well as during their regular breeding cycles. The findings suggest that mares may continue having ovulatory cycles soon after childbirth, regardless of observable signs of readiness for mating.

Study Design and Procedure

• The study measured levels of Luteinizing Hormone (LH), prolactin, and estrogen in the blood of six mares after giving birth. This was done using a technique known as radioimmunoassay, which is a method used to measure minute quantities of substances in a sample.
• LH levels were also tested in blood samples taken every six hours from four regular breeding mares during their oestrus (active sexual period) and at daily intervals during dioestrus (inactive sexual period).

Significant Findings

• The researchers found that the concentrations of estrogen and LH indicate that the mares might be undergoing ovulatory cycles in the post-partum period, regardless of observable signs of active sexual behaviour (behavioural oestrus).
• The levels of prolactin, a hormone that plays a role in ovulation, seemed to increase with likely ovulatory LH peaks, suggesting a potential association between the two.

Observations on LH Levels

• The levels of LH in mares undergoing oestrus significantly increased by the 4th day, peaking approximately a day before the end of oestrus. The peak level of LH was identified as 140 +/- 48 ng/ml.
• After reaching a peak, LH levels rapidly declined and remained at base levels (10 to 20 ng/ml) during dioestrus, the period when the mares were not sexually active.