Comparison of bacteriological qualities of various egg yolk sources and the in vitro and in vivo fertilizing potential of bovine semen frozen in egg yolk or lecithin based diluents

The addition of components of animal origin (egg yolk, milk) to most commercial diluents used to freeze bull semen represents a potential risk of contamination of the doses with bacteria or mycoplasma. A series of quantitative and qualitative analyses were performed to detect microbiological contamination observed in Biociphos plus (a new lecithin-glycerol based freezing salt buffer), in an egg yolk diluent (Triladyl) or in an egg yolk + milk-based (Laiciphos) diluent of bull semen. The 2 diluents containing animal products showed moderate (10 to 60 CFU/mL) contamination (17/17 samples) with bacteria or mycoplasma, or both, while no contamination was observed in the 6 examined batches of Biociphos plus. Biociphos plus was also compared with another commercial diluent (Laiciphos) for use in freezing bull semen intended for in vitro and/or in vivo fertilization. No difference (P > 0.05) could be detected between the 2 diluents for in vitro fertility rates (percentage of cleaved zygotes: 85.7% and 88.0%, respectively, for Laiciphos and Biociphos plus). Similarly, 2 series of comparisons conducted in dairy cows artificially inseminated with semen frozen in either Biociphos plus or Laiciphos showed no difference in fertilizing capacity (tested at 60 to 90 d; P > 0.05) irrespective of the age of the bulls (Trial 1, bulls aged 14 to 15 m.o.; Trial 2, bulls aged 2 to 5 yr, field trials). It is concluded that, in addition to maintaining the fertilizing capacity of bull semen at levels comparable to those observed with standard freezing diluent, Biociphos plus also prevents microbiological contamination by bacteria or mycoplasma, both of which are generally present in the various commercially available sources of egg yolk.