Prolactin secretion in lactating mares before and after treatment with bromocriptine.

This research study investigates the effect of bromocriptine—a dopamine agonist—on the prolactin secretion of lactating mares after childbirth. Results highlighted a significant drop in prolactin and luteinizing hormone levels after the treatment with no notable impact on cyclic ovarian activity.

Introduction to the Research Study

• This research was conducted on and to assess the effect of bromocriptine on prolactin secretion in lactating mares. A total of seven pony and four Thoroughbred lactating mares were used for the study.
• Bromocriptine is a dopamine agonist, which is known scientifically as a compound that activates dopamine receptors in the brain.
• The treatment was initiated anywhere between day 18 and day 28 post-foaling when the prolactin secretion rate had increased.

Methods and Procedure

• Each mare was given a single intramuscular (i.m.) injection of 100 mg bromocriptine.
• Additionally, five of the pony mares also had hormonal measurements taken from the pituitary venous effluent, accessed via cannulation of the cavernous sinus, which is a procedure where a slender tube is inserted into a body cavity to draw out fluid or to insert medication.
• Blood samples were taken before and after the treatments to measure the concentrations of prolactin and luteinizing hormone.

Findings and Results

• Prolactin concentrations fell sharply after treatment (Day 0) but started to increase again on Day 2 in the Thoroughbreds and Day 3 in the ponies.
• It was also observed that the pituitary LH secretion rate declined significantly for two days after treatment.
• However, the treatment did not show any measurable influences on cyclic ovarian activity in the mares.

Significance and Impact of Findings

• This study provides valuable insights into the hormonal changes in lactating mares post-childbirth and the effect of bromocriptine on these changes.
• The decrease in prolactin and LH concentration could potentially inform medical treatments and management strategies for lactating mares, especially in the immediate post-foaling period.
• The absence of any significant effect on cyclic ovarian activity also ensures that the treatment does not impede the mare’s reproductive activity.