When In The Heat Cycle Should A Dog Mate?

When a dog goes into heat, when is the best time to breed her ... The first week, next or towards the end? I have heard different breeder say different things. (John Schmucker - Location Unknown)

This varies dog to dog and is why some breeders attempt to progesterone test to help pinpoint fertility (though testing is not 100% reliable but can help). The fertile period can last about five days and may begin approximately nine to ten days after the onset of heat. However, onset of fertile period can vary after the start of the heat cycle. Some females will only accept a male during this fertile period though others females may allow a male to mount at any time during her cycle while others are not receptive at all. But remember, fertile periods can vary dog to dog.