The Bitch in Heat

 

 The bitch’s sexual cycle. 

A bitch’s sexual cycle is monoestrus (only one ovulation per cycle) with spontaneous (which means that ovulation cannot be triggered by mating, as that in a cat). It comprises four successive stages:

  • Pro-oestrus, a preparatory stage before ovulation;
  • Oestrus, or ovulation proper;
  • Metoestrus, corresponding to the duration of pregnancy and lactation; and
  • Anoestrus or sexual quiescene.

 The length of each phase of the cycle is variable. Only the metoestrus (ordioetrus) phase is of relatively constant length (12±20 days). The bitch is “in heat” or “in season” during the pro-oestrus and oestrus phases of the cycle, a cycle lasting an average of three weeks, but the duration depends on the date of ovulation, which varies among bitches and in the same bitch from one cycle to another. The fact that a bitch ovulates 12 days after the first blood flow in one cycle does not mean that ovulation will occur after the same interval in the following cycle.

 The phases of the cycle

 During pro-oestrus, the hypophysis (pipuitary gland) causes the growing ovarian follicles to secrete hormones known as oestrogens that are responsible for behavioural modifications (the bitch attracts males, seeks affection, and licks her vulva) and physical changes in the bitch. The vulva becomes congested and a bloody discharge appears which attracts males. However, the bitch will not yet allow mating to take place.

 The period during which a male will be accepted corresponds in a general way to oestrus. Often, a postural reflex will appear that causes the tail to be held to the side when the vulva is stimulated. However, this sign should be interpreted with caution; some bitches will accept dogs when they are not in their period of ovulation. During oestrus, the vaginal discharge becomes clear and changes into mucus, which facilitates mating. During this phase, the still-immature ova are released during the oocyte phase. They usually do not become fertile for another 48 hours. 

Unlike those of many species, the ovaries of a bitch begin secreting progesterone several days before ovulation. Progesterone levels in the blood thus increase gradually, whether or not the ova are fertilized. Thus, in dogs, progesterone levels are an indicator of ovulation but not of pregnancy. 

Progesterone secretion then levels off, but lasts through the rest of metoestrus due to secretion by the corpora lutea of the ovaries, from which the ova were released. This hormone prepares the uterus for implantation of the embryo (s) and for pregnancy. Progesterone production falls drastically two months after ovulation, which allows lactation and uterine involution to occur until the sexual organs are completely quiescent (anoestrus).

 To summarize, the period in which the bitch is in heat is relatively short, between ten days and, on occasions, up to three or four weeks. After the heat period bitches secret the pregnancy hormone, progesterone. If they have not been mated, this secretion occurs just the same: this I referred to as pseudo gestation. Some bitches even experience “phantom pregnancies”!

Following the bitch will then be completely sexually quiescent for two to three months-sometimes longer- before coming on heat again. In German Shepherds it is not uncommon for this period to be relatively short and some bitches experience heat periods every four and a half to five months. This is not a sign of hormonal irregularity. It is very difficult at present to reduce this period of sexual quiescence, whatever hormonal treatments are used.

 Mating

The ideal moment

 Given the length of time spermatozoa remain fertile (about 48 hours in the female genital tract), it is possible to optimize the chances of fertilization by making sure that sperm meets egg when both are at the height of their fecundity, to ensure the best fertility and optimal litter size. Ideally, mating should occur within 48 hours following the release of oocytes, so that most of the eggs and sperm can reach the rendezvous point (in the oviducts). The ova remain capable of being fertilized for two days after maturation (in some breeds they even seem t remain for up to four days), which explains why super fecundation by two different males can occur in dogs.

 The most difficult part of the process is observing the biological signs of ovulation as accurately as possible. If mating takes place too early or too late, the bitch is at risk of remaining unfertilized. However, some bitches that have been mated four of five days before their fertile period can nevertheless conceive because the male sperm is able to survive several days in the uterus, at least when the male is young and healthy. There have been cases of live sperm being found over a week after mating has occurred. Very often, however, such early mating result in a small number of puppies because several days after the mating the sperm is no longer so fertile. Your German Shepherd bitch will thus produce only tow or three puppies instead of the eight or ten you might have been expecting. Similarly late mating may result in an undersized litter because some ova will have deteriorated at the time of mating and will no longer be fertile.

 Several complementary tools, of varying precision, are available to breeders for this purpose.

  • Clearing of the vaginal discharge generally signals the end of pro-oestrus, although it is not a reliable indication of ovulation.
  • Systematically mating the bitch about twelve days after the first bloody discharge, then again two days later, is a practical technique if the first discharge is accurately noted. This remains an imprecise method, however, as some bitches (about 20%) do not ovulate during this period, and so do not conceive or conceive only a few puppies.
  • Acceptance of the male or teaser dog and appearance of the tail reflex are not indicative of ovulation. For example, bitches have been observed that allowed mounting from the beginning of pro-oestrus, although they did not ovulate until later (thirty days later in the most extreme cases).

 Many bitches also allow mounting during the false heats before whelping, when urinary infections are present, or when oestrogen secretion by follicular cysts leads to nymphomania. 

  • Use of a galvometer to measure the electrical resistivity of vaginal mucus can lead to a reasonable precise evaluation of the fluidity of vaginal secretions. This parameter usually decreases just after ovulation, signifying the end of the period of oestrogen saturation and thus the rapid replacement of vaginal cells. However, this diagnostic measurement comes tool ate for breeding purposes, since predicting imminent ovulation is more useful than knowing that it has just occurred.
  • Reagent strips that reveal biochemical changes in the vaginal mucus are difficult to introduce far enough into the vagina to avoid contamination by urine. The results are usually imprecise (since the colour change is seen within the three days preceding or following ovulation) and therefore not very reliable.
  • Depending on the stain used, vaginal smears allow direct observation of changes in the vaginal cells related to hormonal variations (particularly oestrogen). This simple, economical technique is now routine used by veterinarians and breeders to obtain a preliminary evaluation of which phase of the sexual cycle a bitch is.

 

( with permission copied from the Royal Canin Encyclopaedia/Aniwa publishing)