Frequently asked questions about small-animal reproduction (Proceedings)

"I want to get my dog bred and I need to know what to look for." – What are signs of heat in the bitch?

The estrous cycle of the bitch consists of proestrus, estrus, diestrus, and anestrus. Proestrus is the first stage of heat, when the bitch first shows swelling of the vulva and exudation of serosanguinous vulvar discharge. Male dogs are interested but she does not allow mounting. Estrus, or standing heat, is characterized by softening of the vulva, a change from serosanguinous to a more tan-colored discharge, and flagging and standing by the bitch. Flagging is lateral deviation of the tail and muscular elevation of the vulva when the perineal region is stimulated. When the bitch is standing to be bred, she allows the male to mount, and holds her rear limbs rigid. Diestrus and anestrus are the latter stages of the cycle, during which there are no characteristic physical changes.

The average bitch cycles about twice a year. She is in proestrus for about 7-10 days, and then in standing heat for about 7-10 days, for a total length of heat of about 3 weeks.

"When should I take my female dog to meet the male?" – How can we optimize breeding management in dogs?

The average bitch ovulates, or releases eggs from the ovaries, on about the second day of standing heat. Traditionally, people have bred dogs on days 9, 11, and 13 of heat (counting the first day of vulvar bleeding as day 1). Other people breed the bitch every other day while she's in standing heat. The latter method should cover the fertile window (from 3 days before to 4 days after ovulation). In bitches with a history of infertility or for whom multiple breedings cannot be performed, timing of ovulation is preferred. Optimal breeding day is 2 days after ovulation in bitches.

Ovulation timing cannot be done by assessment of vaginal cytology. While vaginal cytology can be used to help us determine where a bitch is in her cycle, with estrus defined as 100% cornification with greater than 50% anuclear squame cells and no PMNs present, there is no specific change in cytology that designates occurrence of ovulation.

Measurement of progesterone in serum is the preferred technique for timing of ovulation. Progesterone does not cause ovulation; luteinizing hormone (LH) from the pituitary stimulates ovulation in dogs and other species. A significant rise and fall in serum concentration of LH, which lasts at most 24 hours, occurs 2 days before ovulation. Because the spike in LH secretion is fairly short-lived, and because serum concentrations of LH before and after the peak cannot be distinguished from each other, assessment for the LH peak requires daily collection of blood samples from the estrous bitch, at about the same time each day. This is inconvenient and expensive. Finally, the only commercially available in-house LH assay has been on backorder for an extended period, and assays run at commercial laboratories have such a long turn-around time as to preclude their usefulness for breeding management in bitches.

Bitches undergo a process called preovulatory luteinization, in which the lining of the ovarian follicles containing the eggs begins to secrete progesterone prior to ovulation. Fortunately for us, this increased secretion of progesterone occurs in a fairly uniform manner, allowing us to use progesterone as an indicator of the LH peak and ovulation. Progesterone continues to rise after ovulation. Progesterone can be measured with semi-quantitative in-house tests, which are not as accurate but have short turn-around time, or commercial laboratory assays, which are very accurate but have longer turn-around times. Progesterone interpretation for breeding timing is done as follows: