Anestrus is not the same as interestrus. Anestrus is a variable time after diestrus. Interestrus (diestrus + anestrus) averages 5 - 7 months.
Anestrus lasts 90 - 150 days (anestrus does not include diestrus).
Anestrus is a time of mandatory endometrial repair that has been documented in Beagles.
Anestrus Endometrial Repair
The endometrium is being 'repaired' after the progesterone effects during diestrus for the preceding 60 days.
True anestrus lasts 90 -150 days post whelping, or post diestrus.
Interestrus (anestrus + diestrus) lasts 150 - 210 days after the last estrus.
Fertility is low if at least 90 day anestrus (or a 150 interestrus interval) is not attained. This is because the uterus has not repaired enough to maintain pregnancy. (If interestrus is too short, anestrus can be extended using mibolerone or megestrol acetate, but this will be covered later.)
Anestrus 'events'
The male shows no sexual interest in the female.
The female shows no sexual interest in the male.
The vulva appears normal. It is not swollen or edematous.
The vaginal cytology has very few cells and they are noncornified.
The vaginal wall is very thin and appears pale on vaginal speculum examination.
Progesterone is at baseline concentrations (<1 ng/ml). Even spayed bitches run basal levels of progesterone. This baseline progesterone is probably of adrenal origin.
Prolactin secretion by the pituitary may promote anestrus, because prolactin inhibitors can be used to terminate anestrus (i.e. induce estrus).
