Abstract

Bulls cloned from the somatic cells of genetically elite sires can make a major contribution to genetic improvement and the rate of dissemination of improved genetics within both the dairy and beef industries. However, little is known about the physiology of clone males and the quality of their semen in particular. This paper reports on the semen characteristics of five cloned Friesian bulls, compared to the two ‘Donor’ bulls from which three and two of the clones were derived by nuclear transfer, respectively, and an age matched control bull. Three batches of frozen semen from each of these eight bulls were obtained from a commercial AB centre and analysed. Four straws from each batch of semen were thawed, pooled and made up to 1mL with RSD-1 diluent and sub-samples taken to evaluate viability, motility, morphology, migration (using a synthetic mucus) and DNA damage. Viability, motility and migration assays were performed immediately after thawing (0 hours) and repeated after 3 hours of incubation at 38°C. An additional straw from each semen batch was used to determine sperm concentration and proportion of diploid cells. There were significant differences (P<0.05)between individual bulls in all parameters except diploid cells (0.16 ± 0.05 %), sperm DNA damage (4.41 ± 1.13%) and normal sperm (93.3 ± 6.7%). The differences in viability (range 74.9 to 54.9% at 0 hours; 49.6 to 22.5% at 3 hours), motility (59.2 to 28.3%; 52.5 to 29.2%) and migration (vanguard distance 68.3 to 42.5 mm; 38.8 to 12.5mm and running distance (>150 sperm) 33.3 to 23.3mm; 20.4 to 6.7mm) were greater at 3 hours than at0 hours reflecting individual variation in rate of change in parameters over time. However, examination of the variation between clones within a clonal family or line and between lines revealed that this was similar to the overall individual variation, indicating that members of a clonal family are not more uniform. Nonetheless, these results indicate that the samples of semen from the cloned bulls were as good as those of the original donor bulls and fit for commercial use to potentially disseminate elite genotypes.

JF, Smith, RM McDonald, DN Wells, and NR Cox

Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 297-302, 2007