title: Comparison of density gradient and single layer centrifugation of stallion spermatozoa: yield, motility and survival.
abstract: BACKGROUND
  A new, simpler, technique of colloidal centrifugation has recently been developed, designated single layer centrifugation (SLC). This technique requires evaluation by comparison with a density gradient for its ability to select the best quality spermatozoa and its practicality of use on studfarms.
  
  
  OBJECTIVE
  To compare the effect of 2 methods of colloidal centrifugation, density gradient centrifugation and single layer centrifugation, on stallion sperm motility, yield and survival, using freshly collected extended stallion semen.
  
  
  METHODS
  Aliquots of extended stallion semen from 10 stallions (38 ejaculates) were processed by the 2 methods of colloidal centrifugation. For both uncentrifuged and centrifuged samples, sperm yield was calculated and subjective sperm motility assessed over several days to provide an estimate of sperm survival. Some stored semen samples, held at 4 degrees C overnight, were also available for testing.
  
  
  RESULTS
  For fresh, extended semen, a similar recovery yield of motile spermatozoa was seen for the 2 methods of preparation for single layers and density gradients, respectively. Sperm motility and survival rate were significantly improved by colloidal centrifugation compared to unprocessed ejaculate, without any significant difference between methods (SLC vs. gradient). However, the yield was reduced by 18-20% when cold-stored semen was used for centrifugation compared to fresh semen; and more variation between ejaculates was observed than for fresh ejaculates. Again, sperm motility and sperm survival were improved in the centrifuged sperm preparations compared to stored, unprocessed ejaculates.
  
  
  CONCLUSIONS
  The 2 colloid centrifugation techniques produce equivalent sperm preparations in terms of sperm quality. However, the SLC method would be more practical and convenient for use in the field.
authors.affiliation: Swedish University of Agricultural Sciences-SLU, Department of Clinical Sciences, Division of Reproduction, Box 7054, SE-75007 Uppsala, Sweden.
authors.forename: J M
authors.initials: JM
authors.lastname: Morrell
authors.forename: A M
authors.initials: AM
authors.lastname: Dalin
authors.forename: H
authors.initials: H
authors.lastname: Rodriguez-Martinez
mesh_terms: D000818:Animals; D002499:Centrifugation, Density Gradient / Q000379:methods / Q000662:veterinary; D004542:Ejaculation; D006736:Horses / Q000502:physiology*; D008297:Male; D011156:Population Density; D012662:Semen Preservation / Q000379:methods / Q000662:veterinary; D013048:Specimen Handling / Q000662:veterinary; D013076:Sperm Count / Q000662:veterinary*; D013081:Sperm Motility / Q000502:physiology*; D013094:Spermatozoa / Q000166:cytology* / Q000502:physiology*; D013997:Time Factors; D020858:Tissue and Organ Harvesting / Q000379:methods / Q000662:veterinary