Introduction

In the early twentieth century, Ivanow reported the use of the artificial insemination technique (AI) in pig^1,2. However, the commercial application of AI began at the 1980s³. Its success can be attributed to improvement in the boar:sow ratio, increase of the impact of individual boars in both genetic progress and reproductive efficiency; and limited spread of venereal diseases. Improvement in animal management and quality controls of semen doses and their commercial use have increased the reproductive performance⁴. Conventional artificial insemination (CAI) usually employs 2.5 to 4 billion spermatozoa per insemination in a 70 to 100 ml volume of extender, which is deposited through the cervix into the uterus two or three times during the oestrous period⁵. Boars used for AI can produce 20 to 40 CAI doses containing 2.5 to 3.0 billion motile sperm in 70 to 100 ml of extender. A reduction in the number of sperm per dose would result in a higher number of doses produced per boar with considerable economic saving, thus new strategies towards lowering the number of spermatozoa per dose in AI are constantly under study⁶. Intrauterine insemination (IUI) is an insemination technique that uses a reduced number of sperm per insemination dose respect to CAI⁷. However, data reported about the application of this technique show some discrepancy in the number of sperm cells per dose (which is not yet standardized). Moreover, most of the literature comparing treatments does not include groups with similar sperm number per dose, making it difficult to state whether the results are due to sperm number per dose or to the technique itself⁴.

Boar exposure to sows before insemination is considered to induce myometrial contractions which aid sperm transport; however, there is some uncertainty as to whether boar exposure before IUI catheter insertion is detrimental to the catheter insertion and to whether boar exposure has beneficial effects in CAI. To date, there is not enough information to suggest detrimental or beneficial effects for any approach⁸. Still other matters of discussion arise when considering the advantages and disadvantages of the application of IUI vs CAI. These are the time consumed to insert the catheters for IUI, which is lower for CAI; backflow due to higher volume in CAI; bleeding at the time of inserting the catheters in IUI; and implementation of fixed-time ovulation induction and insemination.

There is information about the use of IUI technology which shows variations not only among countries, but also within each country⁹. In spite of considerable variation among countries and farms, AI can be monitored for success using key measures for quality control and reproductive performance⁸. Thus, a study was performed comparing the reproductive parameters: farrowing rate, litter size, live piglets/litter, stillborn and mummified fetuses between CAI and IUI. Furthermore, it has been analyzed the economic impact on the studied farm and the possible impact on the region.

Material and methods

Results

Discussion

Artificial insemination is widely used and there is constant search for new strategies to achieve higher efficiency. Fixed-time AI, use of high genetic merit boars or changing the site of semen deposition are examples of these attempts to improve efficiency. Watson and Behan⁷ reported farrowing rates of 91.1, 91.8 and 65.8 % for CAI whereas the IUI technique showed rates of 90.5, 90.5 and 86.9, using 3, 2 and 1 billion spermatozoa in 80 ml, respectively. The mean of the litter sizes with CAI were 12.5, 12.6 and 10.6 and with IUI they were 12.3, 12.3 and 12.1, respectively. They demonstrated that only the 1 billion spermatozoa dose with CAI technique showed a significantly lower farrowing rate and litter size. Rozeboom et al¹³, showed that insemination at the beginning of the uterine horn with conventional volumes and spermatozoa numbers (1 billion spermatozoa) produced results similar to insemination in the cervical cavity (4 billion spermatozoa). However, litter size and live piglets/litter were lower in IUI than CAI with those amounts of sperm per dose. Moreover, when 0.5 billion spermatozoa were used for IUI, the farrowing rate decreased approximately 10 % in comparison with the CAI group (78 vs 88.2 %, respectively) and, also, the differences in litter size between both techniques favored CAI (9.4 vs 11.6, respectively). Levis¹⁴ reported similar results. Other work¹⁵ established that the farrowing rate did not differ between CAI using 3.5 x 10⁹ spermatozoa in 100 ml and IUI using 2, 1, or 0.5 x 10⁹ spermatozoa in 50 ml. Peltoniemi et al¹⁶ concluded that uterine insemination did not have a significant effect on live piglets/litter and farrowing rate. The results from those studies do not necessarily reflect the data from similar procedures on other farms. In whole, summarized information about pig reproductive technologies with emphasis in field application suggests that high farrowing rates and litter size are becoming common when using standard AI with only 1.5 billion spermatozoa per insemination¹⁷.

In the present experimental design, all sows were in the same farm, and were inseminated with the same batches of seminal doses; CAI and IUI were equally distributed in the same day and performed with semen from all the three boars. These controlled parameters make it possible to perform a better comparison between the two techniques. Differences in farrowing rates were found using 3 x 10⁹ spermatozoa in 100 ml for CAI and 1.5 x 10⁹ sperm in 50 ml for IUI, that support the change from CAI to IUI in the studied farm. Moreover, although non-statistically significant, the increase in 0.89 on litter size makes the application of IUI more convenient than CAI. To get higher efficiency, AI must be accomplished reducing the number of spermatozoa, in this work the number of spermatozoa and volume of extender used in each dose were reduced to a half.

IUI with reduction in the number of spermatozoa in a fixed volume has already been analyzed¹⁸; however in such work IUI was not contrasted with CAI. They suggested that 0.5 x 10⁹ spermatozoa in 20 ml are sufficient to perform successful IUI, however in this work tested that volume and, the difficulty of handling a 20 ml dose counteracted the possible improvement. The reduction in sperm and doses volume is highly profitable for artificial insemination centers, as the use of superior boars renders twice the doses for IUI than for CAI, thus this feature must be included in future economic impact analyses.

In addition, in the presented experiments, a boar was present when developing CAI and absent for IUI. The presence of a boar for IUI is not recommended due to difficulty to introduce de cannula. Instead, it is recommended for CAI to help in standing and to induce myometrial contractions which aid sperm transport, but additional labor for boar movement is required⁸. Despite the extra aid for sperm transit due to the presence of the boar, farrowing rate did not improve for CAI. This work agrees with the idea of the additional benefit of IUI on the necessity of less boar handling for its application. Since Steverink et al¹⁹, reported that excessive backflow of semen upon CAI has a negative effect on fertilization results when 1 x 10⁹ spermatozoa in 80 ml are used, it was hypothesized that a reduction in volume would improve the efficiency of the technique by reducing the backflow. In this work, no backflow was observed using 50 ml doses, which seems to be an appropriated volume, easy to handle during the procedure. The main obstacle to apply IUI is the complex anatomy of the sow’s genital tract composed by cervical folds and the length and coiled nature of the uterine horns. This obstacle was saved by employing well-trained personnel, who were systematically evaluated throughout the experiment. This may be one of the reasons for the success of IUI in this work. The fact that IUI is time-consuming and requires professional trainers must be included in future economic studies.

To our knowledge, no statistical correlation analysis was made in the precedent works. Interestingly, a statistically positive correlation between live piglets/litter and stillborn was determined in CAI and such correlation was not observed in IUI (Table 2). The Pearson´s correlation coefficient is a measure of the linear correlation between two quantitative variables, so the results presented here may be interpreted as that more services are necessary to obtain more live piglets/litter when using CAI. It is to note that this correlation could be attributed to boar, sow or environmental effects, but results from IUI, which was performed in the same conditions rules out this possibility. With recent data demonstrating the possibility to perform IUI in primiparous sows⁽²⁰⁾, it seems that the use of fewer boars in AI centers and production of more AI doses with reduced number of sperm, per boar, is an interesting aspect to consider to improve the efficiency in swine production.

Considering that 30 minimal doses could be generated by using one single boar and taking into account health, feed, installations and handling costs, the overall costs could be reduced using IUI instead of CAI. As was demonstrated, the change of CAI to IUI using 1.5 x10⁹ spermatozoa in 50 ml doses would be more profitable.

Conclusions and implications

Using 1.5 x 10⁹ sperm in 50 ml, without the presence of boar and inseminating at heat standing with well-trained personal, IUI had a positive impact on the reproductive performance and on the economic parameters of porcine production.