Action: Freeze semen for use in artificial insemination
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- A small controlled trial in the USA found that using frozen semen for artificial insemination resulted in lower fertility in falcons, and a second small trial from the USA found that an American kestrel Falco sparverius had only 33% fertility when inseminated with frozen semen.
- A small trial from the USA found that fertility rates were highest when semen contained 10% dimethyl sulphoxide (DMSO, a cryoprotectant), compared to semen containing 6% or 8% DMSO.
Spermatozoa only survive for a short time and so if artificial insemination is not going to happen immediately, the semen must be frozen. This in itself can damage cells, so a cryoprotectant such as dimethyl sulphoxide or glycerol must be added to protect the cells. Some cyroprotectants (e.g. glycerol) must then be removed by dialysis before insemination.
Supporting evidence from individual studies
A small ex situ study (Parks et al. 1986) found that a single American kestrel Falco sparverius inseminated with frozen peregrine falcon F. peregrinus semen (defrosted and dialyzed to remove glycerol added before freezing) laid six eggs of which two were fertile and one hatched.
A small, controlled ex situ study in New York, USA, in 1986 (Parks & Hardaswick 1987) found that four female prairie falcons Falco mexicanus and one American kestrel F. sparverius had significantly lower fertility when inseminated with frozen sperm (defrosted and dialyzed to remove glycerol added before freezing), compared to two prairie falcons and one kestrel inseminated with fresh semen (25% of 28 eggs for frozen vs. 94% of 17 eggs for fresh semen). Only two prairie falcons and the kestrel produced any fertile eggs from frozen semen. The birds inseminated with fresh sperm were a subset of the larger group and were inseminated with semen from a peregrine falcon F. peregrinus and a peregrine-gyrfalcon F. rusticolus hybrid. Frozen semen preparation took approximately 90 minutes after thawing, during which it was kept at 0-4oC. Insemination used 80 µl (frozen) or 20-70 µl (fresh) semen.
A small ex situ study in 1983-5 (Gee et al. 1993) found that six American kestrels Falco sparverius inseminated with previously-frozen semen produced 14 infertile eggs only when the semen contained 4% dimethyl sulphoxide (DMSO). This compared with 35% of 17 eggs being fertile when 6% DMSO was used; 40% of ten eggs for 8% DMSO and 57% of seven eggs for 10% DMSO. Sperm mobility in semen containing 10% DMSO was lower (44%) than in semen containing 8% or 6% DMSO (61% and 62% respectively). Semen was taken from 15 male kestrels and frozen for between one and 14 months prior to thawing and insemination.
- Parks J.E., Heck W.R. & Hardaswick V. (1986) Cryopreservation of peregrine falcon semen and post-thaw dialysis to remove glycerol. Raptor Research, 15, 15-20
- Parks J. & Hardaswick V. (1987) Fertility and hatchability of falcon eggs after insemination with frozen peregrine falcon semen. Journal of Raptor Research, 21, 70-72
- Gee G.F., Morrell C.A., Franson J.C. & Pattee O.H. (1993) Cryopreservation of American kestrel semen with dimethylsulfoxide. Journal of Raptor Research, 27, 21-25