Physiology of the Ovarian Cycle in the Bitch
Puberty
In most bitches begins at 6 to 9 months of age.
Ovarian Cycle in the bitch is monoestrous. Interval from cycle to cycle varies among breeds and can be affected by environmental cues.
Range: 4 to 13 Months
Average: 7 Months

Ovarian Cycle is Divided into Four Stages
A. Proestrus
Physical turgid swelling of vulva and appearance of a bloody discharge.
Vaginal cytology will change with very early non-cornified epithelial cells increasing towards end of proestrus. Behavior - bitch is restless and secretes pheromones but is aggressively negative towards male becoming more passive towards start of estrus
B. Estrus
Vulva swelling will soften and discharge will be slightly pink to strawcolored. Some females will still have a bloody discharge in estrus which is normal. Vaginal cytology will have a high concentration of cornified epithelial cells with little debris. Behavior - bitch seeks male turns hindquarters towards him, raises pelvic region, waves tail to one side and finally stands for mating by male.
Wolf Heat - (split heat) Have apparently normal heat but go out of heat without ovulation. Followed by another heat 2-6 weeks later (Fertile Heat)

C. Metestrus
Loss of vulva swelling and no discharge. Vaginal cytology is no cornified cells and high numbers of White Blood Cells. Behavior non-acceptance of male
D. Anestrus
Period of ovarian inactivity and no vaginal discharge
Will not return to heat again until at least 4 months
Pseudopregnancy
Extension of metestrus period in which progesterone concentrations remain elevated. Female will have nest building behavior and enlarged mammary glands.

Endocrinology of the Estrous Cycle in the Bitch
Higher Brain Centers
Hypothalamus
GnRH
Anterior Pituitary
FSH LH
Ovary
Estrogen Progesterone

Changes During Estrus of Bitch
Vulva Swollen and Enlarged
Bloody discharge from vulva
Copulation
Aggressive towards Male
Passive Provides sexual posturing to male for copulation
Proestrus Estrus
-8 -4 0 +4 +8 +12
Indicates Day of
Peak in LH

Hormonal Patterns During Estrous Cycle of Bitch
Fertile Period
Ovulation Fertilization
Estrogen
Completion of Meiosis I
Progesterone
LH
-10 -6 -4 -2 0 2 4 8 12 14
Days from LH Peak

Ovulation:
Ova are released from the follicles approximately two to three days following initiation of LH surge.
Fertilization:
Ovulated ova are not ready for fertilization (must complete
Meiosis I) and therefore are not fertilized until Day 4 to 7 following the LH surge.

B. LH Peak
The greatest number of ovulations occur 24 to 72 hours after the LH peak. Breeding can be timed from the LH
Peak to the fertile period 4 to 7 days later.
C. Plasma Progesterone
Plasma progesterone concentrations rise prior to ovulation in the bitch. This occurs because follicles will start luteinization before ovulation. Measurement of serum progesterone concentration can be used as a means to determine day of ovulation and breeding but concentrations can be highly variable and the following are only guidelines.
Baseline Progesterone = 1 ng/ml
Day Preceding Ovulation = 3-4 ng/ml
Day of Ovulation = 4-8 ng/ml

Hormone Concentrations During Pregnancy and Parturition
Parturition
Mating
Prolactin
Progesterone
Corticosteroids
Total Estrogens
0 10 20 30 40 50 60 70
Days of Pregnancy

Breeding
Dog achieves intromission by vigorous thrusting of the hindquarters . The bulbus glandis swells (6X4 cm) in the vagina in which vulva sphincter muscles contract around the penis forming the copulatory “tie”.
First Stage of Coitus
The “Turn”
Second Stage of Coitus

Signs of Impending Parturition
Behavior of bitch is one of nest building, restlessness and seeking quiet, out of sight areas. Vulva becomes swollen, edematous and may have some vaginal discharge.
Relaxation of pelvic and abdominal muscles is a consistent sign of impending parturition. Presence of milk in mammary gland is not an accurate sign.
Decrease in body temperature from 38 to 37 o C just before parturition.

Parturition
First Stage of Labor
Averages 4 hours but can last 6-12 hours
Period in which the cervix dilates
Bitch will be uneasy, refuse food, pant, vomiting and frequently looking at flank.
Second State of Labor
Visible straining of bitch in the sitting position and back against the box. Placental membrane will break and there will be fluid discharge from vulva. Amnion covering the pup will be visible as it passes through the cervix, vagina and out the vulva.
Membrane will rupture spontaneously or through licking of dam.
After the start of labor (active contractions) first fetus cannot be expected to survive more than 6 hours in the uterus. Fetuses should be delivered within 2 hours of each other. Usually interval between puppies is about 30 minutes.

Third Stage of Labor
Passage of fetal membranes should take 5 to 15 minutes.
Dystocia
Definition: Any problem with delaying normal birth of fetus.
Symptoms
Abnormal fetal presentation, position or posture
Strong and persistent labor for 20 minutes without delivery of fetus.
Weak and infrequent contractions for 2 to 3 hours
More than 4 hours from delivery of last fetus (if not last one)
Most common problem is uterine inertia (weak contractions), size of fetus and birth canal.