No, dogs don’t have periods

People incorrectly say dogs have periods because they bleed during their reproductive cycle.

A period is when the endometrium is shed because there was no conception. This happens as part of the menstrual cycle, something humans have.

Dogs have an oestrous (/estrus) cycle. Their body reabsorbs the endometrium if there’s been no conception. An absorbed endometrium can’t be shed and, if the endometrium isn’t shed, there isn’t a period.

 

The oestrous cycle has four stages: proestrus, oestrus, dioestrus and anestrus. (Oestrous being the adjective and oestrus being the noun.)

In proestrus, eggs mature and the endometrium develops. In oestrus, eggs are released, making it the only stage in which pregnancy is possible. For both these early stages, during which the dog is on heat, there can be bloody vaginal discharge.

Dioestrus last longer in non-pregnant dogs than pregnant dogs. The hormone profile for this stage is the same whether pregnant or not. This is why dogs can go through pseudo-pregnancies.

Anoestrus is the longest stage of the cycle, lasting several months. It is the rest stage: the body is neither prepping for pregnancy nor dealing with pregnancy (or the lack of pregnancy).

So, menstrual cycle bleeding gets rid of the egg whereas oestrous cycle bleeding doesn’t get rid of the egg. Menstrual cycle bleeding happens after pregnancy can happen whereas oestrous cycle bleeding happens before and during pregnancy can happen. The bleeding in both cycles is analogous in neither purpose nor timing. If they aren’t analogous, using the same name for both is faulty.