It is difficult to obtain data on the results of natural matings in the dog because no or few of the Kennel Clubs request that the matings should be reported. Available statistics, therefore, only contains information about litters actually born, not about the failures to conceive. Since 1990 the Swedish Kennel Club (SKK) requests that artificial inseminations (AIs) should be reported within 14 days if the litters are to be eligible for registration, and their record by now contains data from around 2500 AIs, and has provided us with a lot of interesting and useful information on reproductive physiology and also reproductive problems in the dog.

MATERIALS AND METHODS

The veterinarians performing the AIs send information to the Kennel Club about the breed, identity, and date of birth of the male dog and the bitch, and whether they have had litters previously, date, and which day of the oestrus cycle the AI was performed, the level of progesterone (when measured), volume of the ejaculate, number of spermatozoa, sperm motility and percentage of abnormal spermatozoa, and whether the semen was deposited in the vagina or in the uterus.

The AIs have been performed in dogs of more than 200 breeds. The semen that has been used has been collected and processed by more than 250 canine semen agencies world-wide, and the AIs have been performed by more than 80 veterinarians.

The influence of time during oestrus when the AI was done, site of semen deposition, and the semen quality as well as the effects of any reproductive problems on whelping rate and litter size were evaluated. We also looked for seasonal effects.

RESULTS

This and a recent study (Linde-Forsberg et al., 1999) are the first to report on significantly higher whelping rates and larger litter sizes when semen is deposited in the uterus rather than in the vagina in the dog, not only when frozen-thawed semen in used, but this also applies for fresh as well as for chilled semen (Tables 1 and 2).

From Table 1 it may appear like results using frozen-thawed semen should be better than when using fresh or chilled semen. The reason for this is that more effort has been put into the frozen semen AIs, in that the bitches are always tested for the best day during oestrus by sampling for progesterone, and practically all the AIs were done into the uterus whereas most of the fresh and chilled semen AIs were done based on vaginal cytology and using vaginal semen deposition. In Table 2 it can be seen that when the results from intrauterine AI is compared, whelping rate by fresh and chilled semen is somewhat better, although this difference is not statistically significant, and litter size is smaller both from vaginal and intrauterine AI when frozen-thawed semen was used.

Table 1. The influence of semen types used in 2210 AIs on the interval to whelping, whelping rate and litter size (least squares means and standard error)

* Figures in a column with no letters in common are significantly different. In the model for litter size and interval to whelping month, breed (>10 litters), semen type, insemination type and interaction between the last two effects were included.

The whelping rate by intrauterine AI was, thus, for fresh semen 36% higher and for chilled semen 50% higher than by vaginal AI, and litter size increased by 0.3 pups per litter for frozen thawed semen, and by 0.6 and 0.7 pups per litter for fresh and chilled semen, respectively.

Duration of the pregnancies were 60-61 days from the last day of AI, which shows that the AIs were done during the fertilization period, i.e., when all the ova were shed and had matured, which is the most optimal time for mating or AI.

Table 2. The effects of semen type, and site of semen deposition (vaginal or intrauterine AI) on the whelping rate and the litter size (least squares means and standard error)

*Figures with different letters are significantly different

Semen that at the time of AI was assessed to be of very poor quality still resulted in a whelping rate of 24.0 % and a litter size of 6.4 pups (S.D. 5.30). Sixteen of the bitches were inseminated despite that they were considered to have been presented too late for AI, and 3 (18.8%) of them whelped a litter of 2, 3 and 11 pups, 59, 60 and 61 days after AI, respectively. This indicates that clinical semen assessment is difficult, and that it may be relevant also to use inferior quality semen, if the breeder is willing to try it and as long it is not suspected to transmit an infection. Those results also demonstrate that it is important to assay for progesterone when deciding the day for AI. The duration of the above pregnancies show that the AIs in fact were done at the optimal time during oestrus, the fertilization period.

Ninety-four bitches had a history of reproductive problems and the whelping rate in this group was only 38.3 % (5.3 pups, S.D. 4.43).

A tendency for a seasonal variation in whelping rate was found for fresh and chilled as well as also for frozen-thawed semen, with the lowest fertility during July (Fig.1). The fact that the results by frozen-thawed semen were also influenced indicates that there may be a female effect, since the frozen semen had been collected and processed at different times of the year.

Figure 1. Whelping rates by month of the year for fresh (dark blue), chilled (pink) and frozen-thawed (yellow) semen, and means (light blue).

REFERENCES

1.  Linde-Forsberg C, Forsberg M. Fertility in dogs in relation to semen quality and the time and site of insemination with fresh and frozen semen. J Reprod Fert 1989; Suppl 39:299-310.

2.  Linde-Forsberg C, Forsberg M. Results from 527 controlled artificial inseminations in dogs. J Reprod Fert 1993; Suppl 47:313-323.

3.  Linde-Forsberg C, Ström Holst B, Govette G. Comparison of fertility data from vaginal vs uterine insemination of frozen-thawed dog semen: a retrospective study. Theriogenology 1999; 52: 11-23.