Estrus is definitely the period of time when the female is sexually receptive and able to breed. Ovulation takes place 24 hrs once the acceptance of the male. As ova survive for approximately four days, a female dog could be impregnated by multiple male in the course of this era. https://petskyonline.com/blog/pet-nutrition-in-the-uae--how-to-choose-the-right-food-and-supplements/