7 THE EFFECT OF A NOVEL RECOMBINANT PROTEASE TREATMENT ON BOVINE SPERM FERTILIZING CAPACITY AND EMBRYO DEVELOPMENT IN VITRO

As described in the IETS Manual (Stringfellow and Seidel, 1995), and endorsed by the OIE, trypsin can be used (for specific pathogens and livestock) to effectively remove certain infectious agents from in vivo-derived embryos for international transport. Because of the multimillion-dollar AI industry for livestock, the OIE has encouraged more research in developing similar decontamination techniques for semen as an added safeguard to animal quarantine for the prevention of disease transmission. Most or all of the earlier studies on embryos used a porcine pancreatic-derived trypsin. Because of more stringent guidelines from international regulatory agencies on the use of animal products, several serine protease recombinants are now available. Previous experiments comparing the porcine pancreatic extract with a recombinant bovine sequence trypsin developed in corn resulted in no statistical difference in cleavage or morula/blastocyst rates. (Mattson et al. 2008 Theriogenology 69, 724–727). An additional in vivo study treating bovine sperm with a yeast-derived human-sequence trypsin resulted in significantly more transferable-quality embryos after the AI of superovulated cows as compared with sperm not treated with trypsin (Blevins et al. 2008 Reprod. Fertil. Dev. 20, 84). The goal of this experiment was to examine the in vitro development of bovine embryos produced from sperm treated with a recombinant trypsin found in a commercially available density gradient centrifugation (DGC) product (Bovipure, Nidacon, Sweden) compared with DGC without trypsin. Oocyte aspiration, maturation, fertilization, and embryo culture were performed using standard methods in 5 replications (n = 2220 oocytes). Semen was collected and pooled from 2 Bos taurus bulls and frozen in an egg-yolk cryodiluent (Biladyl, Minitube). The semen was processed using Bovipure DGC composed of 2 mL of 40% colloid of silane-coated silica particles containing either a yeast-derived human sequence recombinant trypsin containing no animal by-products (n = 1126 oocytes) or the same colloid without trypsin as the control group (n = 1094 oocytes). Both 40% concentrations were layered over 2 mL of an 80% concentration of the same colloid without any additives. The density gradients were centrifuged at 300g for 20 min, after which time the pellets were washed in 5 mL of prewarmed TL Hepes solution (Cambrex) and centrifuged at 500g for 10 min. The resulting sperm pellets were then resuspended in a volume calculated to provide 1 × 106 sperm mL–1, to be used for in vitro inseminations. Results were compared using a 2-tailed unpaired t-test. Cleavage rates for the trypsin-treated sperm (n = 969, 35.8%) and the control (n = 950, 44.3%) groups were not statistically different (P = 0.20). Although more embryos reached the morula to blastocyst stages in the control group (n = 421, 61.0%) than in the trypsinized group (n = 347, 54.7%), these differences also were not statistically significant (P = 0.85). In conclusion, trypsinized Bovipure DGC of sperm before insemination showed no detrimental effects on IVF-derived bovine embryo development.