Dog breeders: need ur help, i have 7 female dogs different breeds..just this summer, my 4 females nag heat.nag gap lang ug weeks. im pretty sure na ako sila gi pa studan pagka 9th,11th and 13th day of heat...pro due dates has pass.wala gyud nag conceived ako mga dogs.i want to know what could be the most probable reasons for this?why wala sila na preggy?please help??