269 THE USE OF A NEW EXTENDER FOR STORING FRESH BOVINE SEMEN FOR LONG PERIODS

Abstract

Processing bovine semen in fresh long life extender for use over 3 to 4 days after collection is a widely used technique in New Zealand (Shannon and Vishwanath 1995 Anim. Reprod. Sci. 39, 1-10). Advantages include greater use of valuable sires, transport without liquid nitrogen, and the possibility of more efficient use of sexed sorted semen. The new extender (Ext. A) also has the advantage of containing no egg yolk. This study compares this new long-life extender (Ext. A) with an existing product (Ext. B) and frozen/thawed semen. Semen from 12 different bulls was diluted to a concentration of 8 × 106 mL-1 and gradually cooled to 16°C. All samples were held at ambient temperature in the dark and motility was evaluated over a storage period of 4 days comparing the extenders. In this part of the trial Ext. A maintained motility better than Ext. B (P = 0.001) during the 4-day storage period (24 h: 90 v. 70%; 96 h: 85 v. 50%). The second part of the trial compared the conception rates (CR) in cows from the use of fresh long-term-extended semen and frozen/thawed semen. On 19 farms, 8546 cows were inseminated with fresh semen stored for 1 to 3 days and 7280 cows were inseminated with frozen semen. The overall CR at 7 to 8 weeks for the 19 farms was 73.7%. On 18 farms within the same farming group, 8498 cows received frozen semen and the CR was 71.1%. Pregnancy results were 2.6% (P = 0.001) higher CR at scanning in herds where fresh semen was used compared with the farms where only frozen/thawed semen was used (73.7 v. 71.1%). In the third part of the trial, semen from 4 different bulls were extended to 1 × 106 mL-1 in Ext. A and held at ambient temperature for 6 days prior to use for IVF. Our lab standard frozen/thawed bull semen was used as a control. Table 1 shows that semen held at ambient temperature in Ext. A for 6 days produced a similar percentage of transferable quality embryos to our IVP control frozen/thawed semen (26.9 v. 25.7%). We conclude that preserved bovine semen in fresh long-life extender for several days offers some advantages in AI and IVP programs compared with frozen semen. Table 1.Fresh semen extender (Ext.A) compared with frozen semen in IVP We appreciate the assistance of Liberty Genetics Ltd.