Breeding
Dogs have an interesting reproductive cycle, rather different to most domestic animals that cycle either seasonally or throughout the year. In the domestic canine, females cycle more or less every six months, with larger breeds tending to cycle less frequently - sometimes only once a year. The physiological reason for this delay is that the corpus luteum - the structure on the ovary that produces progesterone (the hormone of pregnancy) - remains active for at least two months post ovulation, whether or not the bitch is pregnant. This is also the reason why phantom pregnancies occur so frequently in dogs, sometimes with all the signs of a proper pregnancy, including milk production and nesting behaviour, just without the pups!The estrus cycle is quite variable between individuals, but fairly consistent from heat to heat for a specific bitch. We used to use a rule of thumb that ovulation occurred about nine days after the first signs of heat (vulval swelling and bleeding). More recently blood progesterone has been used to predict ovulation very accurately and we have found that the time from the start of the heat period to ovulation can vary from a couple of days up to a few weeks. I saw a bitch recently that only ovulated on day eighteen! The determination of progesterone levels and accurate prediction of ovulation time is particularly useful where artificial insemination is used, especially with frozen semen technology. On the subject of frozen semen, we are now set up to collect and freeze dog semen, as well as perform surgical insemination. Freezing is highly recommended if you have a valuable breeding dog as the samples can be stored indefinitely and hence act as an insurance policy against losing important genetics.
Once mated the gestation period of the dog is around sixty three days from ovulation. As sperm can remain viable for a number of days, this does not necessarily relate to mating date. Confirmation of pregnancy is usually done by transabdominal ultrasound or palpation at about four weeks post-mating.
Most bitches will whelp at night and guessing when this will occur is never simple! One indication of impending birth is a drop is body temperature of about one degree Celsius. This occurs about twenty four hours prior to whelping and is related to an increase in blood estrogen levels. Milk production and mammary gland development can be variable but milk can usually be easily expressed for a couple of days before the birth. Most bitches will stop eating the day before whelping and will show signs of nesting behavior.
Once parturition starts and active abdominal contractions begin the first pup should be born within about thirty minutes. The afterbirth may follow each pup or a few pups may be born first. Normal presentation is head first but pups may be delivered quite normally in a caudal position. Bitches may have a rest period during whelping - this is nothing to be concerned about unless there is active abdominal straining without any obvious progress. It is very important, in my opinion, not to disturb the whelping bitch excessively. Particularly in first time mums or dogs of a nervous disposition, stress may result in cessation of uterine contraction (uterine inertia) and hence lead to dystocia.
Do not hesitate to call your vet if you suspect a problem with whelping. Depending on the nature of the issue we can usually help, either just with advice or in more serious cases by means of obstetrical manipulation or caesarian section. By far the majority of bitches will give birth without any difficulty at all (with the exception of one or two breeds) and require little or no assistance during the event.