Breeding Management of the Bitch

In the bitch the most significant problem with the management of breeding is the large variation that occurs in the time between the onset of proestrous behavior and the timing of ovulation. In addition, the behavior of the bitch and underlying endocrine events are correlated poorly. Often a misunderstanding of these two aspects of reproduction results in the owners choosing the wrong time to attempt to breed their bitches. Often mating occurs at a time remote from the fertilization period, resulting in a subsequent failure to achieve a pregnancy.

The aim of this chapter is to review methods available for the identification of the optimal time for breeding, which include observational assessments, measurement of circulating hormone concentrations, examination of exfoliated vaginal cells, vaginal endoscopy, and ovarian ultrasonography.

Unlike other domestic species, which are polyestrous, a nonpregnant bitch undergoes 57 days of luteal phase after estrus followed by a 5- to 6-month period of anestrus. The monoestrous nature of the bitch and the extended time until the return to proestrus highlight the importance of determining the timing of the period of greatest fertility.

Reproductive Physiology

The basic endocrinologic events in the bitch are not unlike those of other species in that a preovulatory surge of luteinizing hormone (LH) occurs approximately 2 days before ovulation. However, at the time of ovulation, oocytes are immature and cannot be fertilized immediately. Fertilization can occur only after extrusion of the first polar body and completion of the first meiotic division to form the secondary oocyte. Oocytes remain viable within the reproductive tract for 4 to 5 days after they have become fertilizable (i.e., they do not begin to undergo degeneration until 6 to 7 days after ovulation).

When compared with other species, this relative delay in the availability of oocytes for fertilization combined with their lengthened survival time has a significant impact on the onset and duration of the fertilization period of this species.

The Fertilization Period

For all species the fertilization period is the time when oocytes are available to be fertilized. In the bitch this period commences 2 days after ovulation and extends until approximately 5 days after ovulation (Figure 204-1). The fertilization period is the time of maximal fertility, which declines rapidly over the next few days because of degeneration of the oocytes and closure of the cervix, the latter of which prevents sperm from entering the reproductive tract.

Figure 204-1 Schematic relationship among the fertilization period, fertile period, ovulation, and the luteinizing hormone surge.

Although the fertilization period is extremely important in the bitch, it is not the only period of time during which a breeding can result in pregnancy. Intrauterine insemination after closure of the cervix has resulted in pregnancies with a small litter size (presumably because of reduced fertilization rate in aging oocytes), whereas breeding before the fertilization period can result in pregnancy as long as the sperm survive until the fertilization period in the female reproductive tract.

The Fertile Period

The fertile period is the time during which a breeding could result in a conception. Therefore it includes the fertilization period, but it also precedes the fertilization period by several days because sperm can survive within the female reproductive tract (see Figure 204-1). In some stud dogs, sperm can survive for up to 7 days within the reproductive tract of some females. In this situation, the fertile period commences 5 days before ovulation (i.e., sperm surviving for 7 days fertilize oocytes 2 days after ovulation).

However, not every stud dog produces sperm able to survive such a protracted period of time within the female reproductive tract. Dogs with poor semen quality generally have reduced sperm survival, and this accounts largely for the poor fertility seen in these individuals. Sperm that have been preserved (chilled or frozen) also have a short survival time within the female reproductive tract. Therefore the potential fertile period is a feature of male fertility combined with female physiology.

The period of peak fertility for natural breeding with fertile animals ranges from the day of ovulation until 4 days after ovulation (Table 204-1). The period of peak fertility commences before the true fertilization period because sperm are required to mature within the female reproductive tract; this process of capacitation may take approximately 6 hours or more. Litter size does not seem to depend on which of these days that bitches are mated. Breedings earlier or later commonly result in lower pregnancy rates and smaller litters. For the accurate prediction of the optimal time to breed, either the day of the onset of LH surge or ovulation should be identified. However, identifying these events can be challenging and imprecise.

TABLE 204-1

Timing of Events in Relation to the Luteinizing Hormone Surge and Ovulation in the Bitch

Event	Days from Luteinizing Hormone Surge	Days from Ovulation
Period of potential fertility: the fertile period	3 days before LH surge until 7 days after LH surge	5 days before ovulation until 5 days after ovulation
Approximate time of oocyte maturation	4 or 5 days after LH surge	2 or 3 days after ovulation
Period of actual fertility: the fertilization period	4 or 5 days after LH surge until 7 days after LH surge	2 or 3 days after ovulation until 5 days after ovulation
Period of peak fertility	2 days after LH surge until 6 days after LH surge	The day of ovulation until 4 days after ovulation
Preferred breeding time using natural service or fresh semen insemination	2 days after LH surge until 6 days after LH surge	The day of ovulation until 4 days after ovulation
Preferred breeding time for males with poor quality semen or frozen-thawed semen insemination	5 to 6 days after LH surge	3 to 4 days after ovulation

LH, Luteinizing hormone.

Modified from England GCW, Concannon PW: Determination of the optimal breeding time in the bitch: basic considerations, accessed Sept 1, 2002, from www.ivis.org.

Observational Assessments

Although in other domesticated species there are reasonable relationships between the time of ovulation and several aspects of the reproductive cycle, in the bitch this is not the case. The time of ovulation in relation to the onset of proestrus and the behavioral characteristics typical of estrus have a poor relationship with the fertilization period.

The Number of Days from the Onset of Proestrus

Many breeders rely on counting the number of days from the onset of proestrus and believe that bitches ovulate a defined number of days from the onset of this event. This is not the case for all breeds (Figure 204-2). The duration of proestrus is variable among bitches (3 to 21 days). Although the “average bitch” may ovulate 12 days after the onset of proestrus, some bitches ovulate as early as day 5, and others as late as day 30 after the onset of proestrus.

Figure 204-2 The relationship between day of ovulation and the onset of proestrus for normal fertile bitches.

The large variation in the time of ovulation (and therefore the fertilization period) explains most of the infertility that arises when bitches are bred on the twelfth and fourteenth day after the onset of proestrus, which is common breeding practice. Furthermore, the events of one estrus are not necessarily the same at the subsequent cycle; some bitches may vary in the day of ovulation by as much as 12 days from one cycle to the next (e.g., they ovulate on day 12 of one cycle and on day 24 of the next cycle).

The Onset of Estrous Behavior

In some species the onset of the behavioral signs of estrus (acceptance of mating) can be used to determine the optimal time for breeding. However, in the bitch there is often a poor correlation between endocrine events and behavioral events. Studies on laboratory-kept bitches suggest that the onset of standing estrus occurs, on average, at the same time as the onset of the LH surge (Concannon et al, 1977). Using these data, 3 or 4 days after the onset of standing estrus would be a suitable time for mating. However, as stated previously, in many other bitches the behavioral responses correlate poorly with the underlying hormonal events. This may be because bitches are housed away from the male and introduced only when the breeder considers the time to be correct, thus inhibiting natural courtship responses; or it simply may represent greater variation than was thought originally. A further complication is that in some bitches the behavioral changes may be displayed poorly and therefore the onset of estrus may be indistinct.

It may be that, with regular examination using a standard stimulation (e.g., possibly with the use of a teaser male), the value of assessing estrous behavior could be improved. However, male dogs have been shown to demonstrate clear preferences for some females over others, thus making the interpretation of this criterion difficult to assess. When relying solely on the receptivity of the bitch, clinicians should plan breeding shortly after the onset of estrus and continue throughout the period of female receptivity.

< div class='tao-gold-member'>

Only gold members can continue reading. Log In or Register to continue