Expectations surround sex cell breakthrough
Expectations surround sex cell breakthrough
By Marianne Curtis
NEW freezing technology is allowing sexed semen conception rates to match those achievable with conventional semen, allowing more producers to potentially benefit from deciding the gender of calves.
Since sexed semen was launched by Cogent two years ago, the company has been searching for ways to improve conception rates, which are about 10% lower than with conventional semen, says researcher Innes Drummond. "With sexed semen there are fewer sperm in semen straws, so the margin for error when thawing straws is less."
But a new freezing technique which is kinder to sperm allows more to survive the freezing/ thawing process improving the chance of conception, says Mr Drummond. "In traditional liquid nitrogen vapour freezing techniques, ice crystals are irregular with jagged edges, which can lead to rupture of some sperm membranes, killing or weakening them.
"However, a new freezing technique – where semen straws are moved at a fixed speed across two chilled blocks held at 5C and -50C – causes ice crystals to form in parallel lines, allowing sperm to rest between them unharmed."
The new Harmony Freeze technique also halves the amount of glycerol needed during the process. Glycerol is used to protect sperm during freezing, but can also be toxic. "Using a lower concentration of glycerol improves sperm viability," explains Mr Drummond.
Recent changes to bull diets will also improve sperm viability, he adds. "Bulls producing semen for sexing are being fed omega-9 long chain fatty acids via oil added to their diet. Sperm from bulls fed this diet have more pliable cell membranes than those fed diets without omega-9 fatty acids. This makes them more tolerant to stress caused by semen handling, chilling, freezing and thawing."
The combination of a new freezing technique and alternative diet is evident when sperm motility is examined after thawing, says Martin Hall. "With the liquid nitrogen vapour method, used to freeze sperm for the last 40-50 years, post-thaw motility is usually 40-45%. With the new freezing technique it is 65-70%."
Results using semen frozen using the new technique on Cogents own farms are promising, says Mr Hall. "We have been using this technique for all our sexed semen since Christmas and early indications show conception rates on a par with conventional semen. We are hoping follow these with independent trials in late summer."
The new freezing technique could also prove useful for conventional semen. "The priority has been to develop the technique for sexed semen, but we are looking at whether it can be used successfully for bulls whose semen freezes poorly." *
FREEZINGSEXEDSEMEN
• New method developed.
• Reduces sperm damage.
• Improves conception rates.