Grass greenness flush can influence breeding phenology and fertility in equatorial thoroughbred mares in the absence of photoperiod variation.

Reproductive phenology is an important trait subjected to natural selection. Current horses in America belong to the Palearctic original populations after being introduced by European colonizers. Photoperiod variation is the main environmental factor for the adjustment of reproductive timing in horses, but is absent in equatorial areas.

Reproductive phenology of Creole horses in Ecuador in the absence of photoperiod variation: The effects of forage availability and flooding affecting body condition of mares.

Horse reproduction tends to be seasonal. The main adjusting factor in their original temperate ranges is photoperiod variation, although it is absent in equatorial areas where horses were introduced by European colonizers. Hence, dates of reproduction in these areas may be influenced by factors affecting mares' conditions and the success of foaling.