14 SUBLETHAL HYDROSTATIC PRESSURE TREATMENT IMPROVES FRESH AND CHILLED BOAR SEMEN QUALITY IN VITRO AND IN VIVO

Abstract

Insemination of fresh boar semen is a widely used production tool in swine breeding and meat production. Although the success rates of routine insemination procedures are satisfactory, improvements are still needed to reduce production costs; moreover, the reduced litter size of gilts compared with sows still calls for further solutions. Sublethal high hydrostatic pressure (HHP), applied to fresh boar semen before cryopreservation, was reported to improve post-thaw motility and litter size. Proteomic studies revealed a treatment-related increase in different proteins that may contribute to increased fertility (Huang et al. 2008 Anim. Reprod. Sci., in press). Herein, we provide data showing how the same treatment influences the in vitro lifespan of semen stored at 15°C and fertility at routine fresh semen insemination. For in vitro evaluation, semen was collected from Seghers boars (n = 7), extended, cooled to room temperature, and then split into 2 groups. Semen in the treatment group was filled into sterile transfusion bags and treated with 300-bar pressure for 90 min at 25°C in a computer-controlled pressure device (Cryo-Innovation Ltd., Budapest, Hungary). After treatment, both groups were placed into a cooling thermostat set to 15°C. Total and progressive motility was assessed daily for 12 days by a computer-assisted semen analysis system. For in vivo evaluation, semen (boars, n = 14) was prepared, split, and treated as described above. Hungarian Large White × Hungarian Landrace sows (n = 103) were then inseminated with treated or nontreated semen. Inseminations were done in the routine production of 2 swine farms. For statistical analysis, a generalized linear mixed-effects model was used, with P < 0.05 regarded as significant. Results showed that the reduction of both total (TM) and progressive (PM) motility of the treated samples was significantly slower compared with control samples. On Day 5, the ratio of live (TM) to PM cells (control v. HHP treated) was as follows: TM, 55.4 v. 64.6%; PM, 36.6 v. 46.4%. On Day 11, the ratio of TM to PM cells was as follows: TM, 43 v. 53%; PM, 27 v. 31.4%. Mean pregnancy rates and litter weights were not different between the 2 groups (73 v. 74%; 16.34 v. 16.37 kg; HHP treated v. nontreated, respectively). However, the effect of treatment on the litter size was significant (12.4 v. 11.4; HHP treated v. nontreated). Moreover, there was a significant difference in treatment effects between the gilts and the sows: whereas treatment had no significant effect on the litter size of the sows (P = 0.47), the litter size of the gilts increased (P < 0.001), with a mean of 2.55 ± 0.83 (SE). This preliminary report shows that HHP-treated semen survived chilled storage better. The HHP treatment also increased the average live and total litter size achievable with fresh semen insemination, with litters not being different from the controls in weight, sex ratio, or stillbirths. The increased litter size was more evident in the case of the gilts. Further field trials are being conducted.

This trial was supported by OMFB-00364/2007.