This is the time when the ovaries return to cyclic activity by producing eggs or follicles. During transition, the follicles do not always ovulate due to low levels of luteinizing hormone. Seventy-five percent of mares in a temperate climate, such as Canada, respond to the normal increase in day light as experienced in the spring. The other twenty-five percent of mares living in temperate climates, cycle year round. Horses residing at the equator also cycle year round.
Ponies are more seasonal than horses.
Natural selection may have favoured a more confined breeding season for ponies which evolved under harsher climatic conditions than horses. This would ensure that foals were born under the best climatic conditions. The natural breeding period of May to July is the period of highest ovarian activity. May. Many farms use artificial lighting to induce an earlier onset of regular ovarian activity. Artificial lighting is used to increase the day length to14-16 hours.