Seasonal reproduction in the mare: possible role of plasma leptin, body weight and immune status.

The study examines the possible influence of leptin levels, body weight, and immune status on the reproductive cycles of Lusitano mares, suggesting that body weight and leptin levels could have a direct relationship and could help restart or maintain ovarian activity. However, the research finds no significant impact of seasonal changes in ovarian activity on the horse’s immune status.

Study Objective and Methodology

• The research aimed to analyse the roles of leptin (a hormone that regulates energy balance by inhibiting hunger), body weight, and immune function on the reproductive cycles of Lusitano mares across different seasons. This included the transition from active reproductive cycles to periods of inactivity (anestrus), during anestrus, and when reproductive activity resumed.
• Over two years, 10 mares in good health were observed each year. Their reproductive status was monthly monitored using ultrasonography and plasma progesterone measurements. In the second year of observation, all mares were also weighed.
• The assessment of progesterone and leptin levels was carried out through radioimmunoassay (RIA), a technique used to measure the concentration of specific antigens.
• The immune status of these mares was evaluated by looking at phagocytosis (the ability of a cell to engulf particles) and oxidative burst of neutrophils (a process where these white blood cells release reactive oxygen species to kill pathogens). The counts of different types of lymphocytes were also taken into consideration.

Findings of the Study

• Regarding immune status, the research did not find any significant change in phagocytosis, oxidative burst, or circulating lymphocyte subsets during anestrus or any phase of the estrous cycle. This suggests that the mare’s immune responsiveness does not change with seasonal fluctuations in its ovarian activities.
• The study suggests a direct relationship between the mare’s body weight and plasma leptin levels.
• Higher levels of leptin could potentially be linked with the restart or maintenance of the mare’s reproductive cycles.

Implications of Research

• This research sheds light on the understanding of the relationship between a mare’s reproductive cycles and factors such as body weight and leptin levels. This could be beneficial to boost the reproductive health of horses especially those used in breeding programs.
• Though further research is needed, the findings suggest that higher concentrations of leptin, associated with greater body weight, could play a role in the maintenance or resumption of ovarian activity in Lusitano mares.