Diestrus

The Reproductive Cycle

The reproductive cycle in dogs varies tremendously

depending on breed and size of the animal. Puberty

may occur as early as six months old in small

breeds and as late as two years old in larger breeds.

On average, you can assume that the first estrous

cycle (heat cycle) will occur between six and 12

months of age.

Duration of Reproductive Cycle

The duration of the estrous cycle in a particular dog

is fairly consistent over time, but again, there’s a

great deal of variability between breeds. Some

breeds will cycle once every 4 months (e.g. German

shepherd) while others will cycle once every 12

months (e.g. Basenji). In general, older bitches cycle

less frequently than when they were younger.

The Canine Estrous Cycle

Diestrus

Diestrus lasts from 60 to 90 days in a dog that doesn’t become pregnant or approximately 63 days in a dog that does become pregnant.

Clinical Signs

Physiologically, the uterine glands undergo hypertrophy and hyperplasia. The cervix constricts and vaginal secretions become tenacious.

During this phase of the reproductive cycle, the bitch refuses to accept the

sexual advances of the dog.

Female Unreceptive to Male

Diestrus is characterized as the phase after the “heat” cycle. At this point one of two things can happen:

1. The bitch can become pregnant.

2. The bitch does not become pregnant, but has a higher chance of Pyometra after the first heat.

Progesterone

In this period the corpus luteum (CL) is present. The CL are fully functional and secrete increased large quantities of progesterone.

PyometraAs a consequence of the bitch’s long exposure to progesterone when she’s not pregnant, she’s prone to a condition called pyometra if not spayed. Pyometra occurs when the uterus fills with bacteria and white blood cells. If untreated, pyometra can lead to fatal illness due to toxins secreted into the blood stream or the uterus actually rupturing. Thus, it’s highly recommended to spay a bitch that will not be used for breeding.

Pyometra

Pregnant Canine

Vaginal Cytology

Vaginal cytology specimens are easily and quickly collected and prepared. A saline moistened cotton swab is inserted through the vulvar lips into the vagina. The swab is angled craniodorsally to avoid the clitoral fossa. A clean otoscope may be used to guide the swab and to provide a light source for visual guidance. Once the swab is located cranial to the urethral orifice, the swab is rotated slightly to exfoliate and collect the cells.

After the swab is removed from the vagina, the cells are transferred to a clean glass slide by rolling the swab along the surface of the slide. Intact cells are obtained during transfer by rolling the swab. In contrast, back and forth smearing of the swab to transfer the cells will cause sever cellular distortion and rupture. Once the cells have been transferred, the slides are air dried, stained with new methylene blue stains, and examined microscopically.

What you will find…..

Diestrus characterized by a decrease in superficial cells, increase in smaller intermediate cells, and presence of neutrophils. Cytologically, diestrus may appear similar to early proestrus

Vaginal Smear

In diestrus, the vaginal discharge will cease and the epithelial cells of the reproductive tract quickly appear small and round again. White blood cells can be seen in very high numbers during the first few days of diestrus. This is normal since their function is to clean up the cellular debris left behind by estrus.

Cell populations change abruptly in diestrus. Superficial cells decrease by 20% and smaller intermediate cells increase in number. Neutrophils often reappear and may contain phagocytosed erythrocytes and bacteria. Cytologically, this stage of the reproductive cycle can look very similar to early proestrus. Therefore, serial cytologic sampling is required to make the distinction.

Diestrus Cytology

The End