Effect of daily clenbuterol and exogenous melatonin treatment on body fat, serum leptin and the expression of seasonal anestrus in the mare.

This research investigated the effects of certain pharmacological treatments on the body fat, serum leptin levels, and the onset of anestrus (the period of sexual inactivity or quiescence) in mares. They found that while certain treatments led to a decline in body fat and leptin levels, it did not change the onset of the anestrus period.

Objective of Research

• The research primarily aimed to understand if pharmacological manipulation of body fat and leptin could influence the anestrus period in mares. This is significant due to the implications it could have on the timing of the equine breeding season.
• It focused on the administration of clenbuterol, a beta(2)-adrenergic receptor agonist, with and without continuous treatment with melatonin, to test its impact on body fat, leptin levels, and anestrus onset.

Research Method and Experiments

• Two experiments were conducted. In the first, eight mature mares were given a daily dose of clenbuterol from October to January, and six mares remained untreated. In the second experiment, clenbuterol was given to eight mares daily from June to December; eight mares received melatonin implants, and seven mares underwent both therapies.
• Melatonin treatment was included to confirm prior findings that constant melatonin treatment did not advance the timing of anestrus.

Key Research Findings

• Both experiments found that leptin concentrations and body fat declined in response to daily clenbuterol treatment. However, this effect was lessened in mares also treated with melatonin.
• Despite the decline in body fat and leptin levels in mares treated with clenbuterol, the timing or proportion of mares entering anestrus remained unchanged.
• These results suggest that while pharmacological intervention can alter body condition, it does not modify the mechanisms that control the seasonal anestrus period in mares.