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Post-cervical artificial insemination (PCAI) or intrauterine insemination is successfully used in primiparous and multiparous sows and is a well-established technique in these animals. However, there are still few or only recent studies on the technique used in gilts, which present different results and approaches.
The application of the PCAI technique in gilts is still limited by the difficulty of passing the catheter through the cranial part of the cervix, which clearly represents a significant barrier due to its smaller dimensions. Therefore, due to this limitation, it is still necessary for farms to keep both techniques (traditional and post cervical) in their routine, and semen suppliers must produce semen doses with different volumes and number of sperm cells.
Artificial insemination
For a long time, PCAI has not been recommended for gilts due to the difficulty of catheter insertion. However, when it is possible to perform PCAI on gilts, there is no difference in reproductive performance compared to traditional (cervical) artificial insemination (Will et al., 2021a). To date, there are few studies that have included this category of females, or have used catheters specifically for gilts. However, with the improvement of catheters (more flexible material), the advice of eliminating boar exposure during PCAI, as well as the increased experience of the workers, the success rate of PCAI application in gilts has increased. Faced with this new scenario, from 2017 onwards, studies of PCAI in gilts were resumed and have been published in the last few years. However, the success rate of applying the technique in gilts continues to diverge between studies (Table 1).
Table 1. Reproductive performance using intrauterine artificial insemination (IUAI) with different numbers of spermatozoa (spz) and semen dose volumes in gilts.
| Reference | n1 | AI technique | Type of catheter+ cannula2 | Nº spz (x109)3 | Vol (mL)4 | Conception rate (%) | Farrowing rate (%) | TB5 | SR6 (%) |
|---|---|---|---|---|---|---|---|---|---|
| Dimitrov et al. (2007) | 28 | CAI7 | - | 3.0 | 100 | - | 87.5 | 10.3 | - |
| 19 | PCAI8 | - + M | 1.5 | 50 | - | 89.5 | 9.1 | - | |
| Hernández-Caravaca et al. (2017) | 47 | CAI | - | 3.0 | 80 | - | 93.6 | 13.7 | - |
| 56 | PCAI | M + M | 1.5 | 40 | - | 82.6 | 13.1 | 19.6 | |
| 54 | PCAI | G + M | 1.5 | 40 | - | 93.3 | 13.2 | 37.0 | |
| 63 | PCAI | G + G | 1.5 | 40 | - | 84.3 | 13.9 | 60.3 | |
| Tenus et al. (2017) | 273 | PCAI | - | 2.5 | 80 | - | 89.4 | 11.6 | - |
| 279 | PCAI | - | 1.5 | 40 | - | 91.8 | 11.8 | 91.4 | |
| Suárez-Usbeck et al. (2019) | 324 | CAI | - | 3.0 | 90 | 91.4 | 85.8 | 18.3 | - |
| 248 | PCAI | G + G | 1.5 | 45 | 92.3 | 88.7 | 18.5 | 77.5 | |
| Llamas-López et al. (2019) | 130 | CAI | - | 2.5 | 85 | 87.5 | 83.6 | 13.7 | - |
| 1036 | DpCAI9 | G + G | 1.5 | 45 | 89.8 | 87.5 | 13.1 | 88.9 | |
| Will (2021b) | 158 | CAI | - | 1.5 | 50 | 96.5 | 93.7 | 14.5 | |
| 159 | CAI | 2.5 | 80 | 97.7 | 95.6 | 14.5 | |||
| 90 | PCAI | M +G | 1.5 | 50 | 98.0 | 94.4 | 14.8 | 58.9 | |
| 97 | PCAI | M + G | 2.5 | 80 | 95.3 | 93.8 | 14.5 |
1 Number of females inseminated. 2 Cervical catheter for multiparous sows (M) or gilts (G) + post cervical ccannula used in multiparous sows (M) or gilts (G). 3 Number of spermatozoa (spz) in insemination dose (x 109). 4 Volume of insemination dose. 5 Number of total piglets born. 6 SR: Post cervical catheter passage success rate. 7 CAI: Cervical artificial insemination 8 PCAI: Post cervical artificial insemination. 9 Dp-CAI : Deep cervical Artificial Insemination. There were no differences between treatments in any study. Source: Will et al. (2021a).
What makes it difficult to understand the success of catheter passage is the definition used to define the passage percentage, which is often not clear in the methodological description of the studies. This is because the passage percentage may consider females in which it was possible to insert the cannula in all inseminations during estrus, the percentage of females that received at least one PCAI during estrus, or even the percentage of post cervical catheter passage per insemination performed. In addition, the lack of information on the dimensions of the equipment used makes it difficult to identify those with the greatest potential applicability for PCAI. There is also a lack of standardization regarding the characteristics of gilts at the time of insemination (age, weight, body condition, and number of previous estruses), which makes it more difficult to conclude on the possibilities of using PCAI in gilts.
Given the difficulty of inserting the catheter through the cervix, the development of specific devices for PCAI in gilts was considered. In this regard, Will et al. (2021b), using a specific cannula for gilts (3.0 mm in diameter, reaching up to 13 cm beyond the tip of the catheter), observed post cervical catheter insertion success rates close to 60%, considering gilts that allowed cannular insertion (≥ 7 cm) in all inseminations performed during estrus. Moreover, in the same study, they observed that, on average, two attempts (with an interval of 5 minutes between them) were needed to pass the probe. Thus, the time to perform the technique was not reduced compared to CAI, due to the difficulty of passing the probe through the cervix, which shows that the application of PCAI in gilts remains a challenge.
Another question is the effect of gilt age and weight on the success of PCAI. Will et al. (2021b) observed a higher chance (>60%) of catheter insertion in heavier gilts at first estrus detection (≥ 124 kg), and in older gilts (≥ 225 d) and with a higher body condition score (>3) at the time of insemination (Table 2). Therefore, a possible effect of gilt age and weight on the success rate of PCAI application should be considered. Representative information considering probe passage in different genetic lines is still lacking due to differences in physical conformation, as well as age and weight recommendations for first insemination. These characteristics are relatively easy to measure in routine on-farm processes and to understand their effect on PCAI recommendations in gilts.
Therefore, the use of the PCAI technique in gilts remains a challenge due to difficulties in the rate of passage of the cannula through the cervix. In addition, the time required for PCAI, compared to multiparous sows, tends to be longer. The possible effects of genetic factors and the physical characteristics of gilts still need to be further understood in order to improve the technique and recommend its use on a large scale.
Table 2. Success rate (%) of post cervical probe passage through the cervix in gilts according to different ages, visual body condition score (BC), caliper units, and the weight at the estrus before insemination.
| Physical variables | n | Age (days)1 | P values | ||||
|---|---|---|---|---|---|---|---|
| ≤224 | 225-241 | ≥242 | Age | Variable | Age*Variable | ||
| n | 80 | 157 | 82 | ||||
| BC1 | <0.01 | 0.27 | 0.09 | ||||
| 2.5 | 65 | 36.8by | 60.6by | 61.5by | |||
| 3 | 177 | 53.1by | 57.0by | 54.8by | |||
| >3 | 77 | 33.3by | 71.1bx | 88.9ax | |||
| Caliper1 | 0.01 | 0.34 | 0.10 | ||||
| <13 | 68 | 52.4bx | 55.9bx | 61.5bx | |||
| 13-14 | 170 | 47.7bx | 60.2bx | 55.8bx | |||
| >14 | 81 | 33.3bz | 67.5by | 88.5ax | |||
| Weight (kg)3 | 0.01 | 0.04 | 0.06 | ||||
| <124 | 78 | 36.7bx | 50.0bx | 42.9bx | |||
| 124-140 | 162 | 60.5ax | 59.6bx | 62.9ax | |||
| >140 | 79 | 25.0by | 76.5ax | 81.8ax | |||
1 Data for the variables age, BC, and caliper were collected at the time of insemination (2nd estrus). 2 Physical variables. 3 The variable weight was measured in the estrus prior to the insemination. In this study, the success rate was defined as the percentage of gilts that allowed the passage of the post cervical catheter through the cervix in all inseminations they underwent during estrus. The interaction was considered a trend (P > 0.05 and P ≤ 0.10). a-b the column indicates the trend of the difference between body variable classes. x-z in the row indicates the trend of the difference between age classes. Source: Will et al. (2021a).
