All large swine companies use artificial insemination (AI) with fresh or frozen semen and the interest in using frozen semen is on the rise in China. We evaluated the fertility of cryopreserved semen from two paternal lines of Duroc and Pietrain pigs on a sow farm.
Semen extenders and straws, glycerol and Equex Paste, a programable freezer (IceCube) and a CASA system (SpermVision) were purchased from Minitube USA (Verona, WI, USA). Fresh eggs were obtained from a local market. In Experiment 1, fresh ejaculates, obtained from 9-month or older Duroc and Pietrain boars from a single stud, were frozen and thawed following a previously published protocol . Only samples with equal or greater than 60% progressive motility post-thaw were used at a dose of 2.0 x109 motile sperm per insemination. Estrous crossbred sows of 2-4 parity were bred twice daily, with AI PM-AM or AM-PM after standing heat was first detected in the morning or afternoon, respectively. The two-dosing time interval was about 16 h. Post-cervical catheters were used to deposit the semen in the presence of a sexually mature boar. The conception rate determined by ultrasonography 35-day post breeding, and the farrowing rate, were recorded. In Experiment 2, post-thaw semen pooled from 18 Duroc boars was used to breed crossbred estrous sows with three different AI doses: 2.0, 1.4 and 0.8x109 progressively motile sperm per insemination using the same breeding schedule. Spermac stain was used to evaluate sperm membrane and in particular acrosome integrity of sperm . The data were analyzed using SPSS 20 Software.
In Experiment 1, the frozen semen from Duroc and Pietrain boars was used to inseminate 26 and 22 estrous sows, resulting in pregnancy rates of 73.08%, and 72.73% and farrowing rates of 69.23% and 59.09%, respectively. The percentages of intact acrosomes in the frozen-thawed semen were 80.4±3.18 and 61.69±3.9, for Duroc and Pietrain boars, respectively (P<0.05).
For Experiment 2, the doses of pooled post-thaw Duroc semen used to inseminate 26, 29, and 28 estrous sows with 2.0, 1.4 and 0.8 x 109 progressively motile sperm, resulted in 73.2 ± 5.78%, 75.9 ± 5.25% and 78.5 ± 1.28% pregnancy, and 69.4 ± 4.8%, 75.9 ± 5.25% and 75.2 ± 4.49% farrowing rates, respectively. No statistical differences in pregnancy and farrowing were found among the three doses. Concurrently the overall farrowing rate with fresh semen for sows bred August 2018 (summer) was 83% for the same farm.
Following the same freezing protocol, Duroc semen had higher post-thaw acrosome integrity of sperm than Pietran semen. A different freezing protocol may be needed to achieve better post-thaw acrosome integrity for Pietran semen. It was possible to reduce the motile dose of Duroc sperm per insemination from 2.0 to 0.8 x 109 without a loss of fertility.