29 September 1995

Semen capsule system trims conception odds

By Sue Rider

CONCEPTION rates in heat-synchronised cattle can be increased by 10% when the sperm inseminated is enclosed in tiny bags.

US research has designed a technique to "micro-encapsulate" sperm. The benefit is that once inseminated, it is released inside the cow over an extended period of about three days.

"The supply of sperm is ready to fertilise the egg over a longer period," USresearcher Dr Nebal told the 30th Symposium on Animal Breeding and Reproduc- tion in Milan. He said the phased release of sperm would ensure timing of insemination is less critical.

Given that synchronised cattle come on heat over an extended period, the technique helps overcome difficulties of heat detection, said Dr Nebal. The phased semen release ensures sperm is present inside the cow at the critical 12 hours after standing heat stage when the conception rate is best.

One dose of encapsulated semen contains 50 capsules or bags. Within each is up to 100,000 sperm – to give 5m encapsulated sperm a straw. The dose rate required is considerably lower than the 10-15m sperm needed when cows are served with uncapsulated sperm.

"The technique also offers the potential to reduce the concentration of sperm needed in a straw – so increasing the availability of high demand sires," said Dr Nebal.

To encapsulate the sperm it is treated with a seaweed-type gel, sodium alginate. Binded to the gel-like droplet is a semi-permeable polyamine membrane. With this in place, the gel is removed and the sperm held in the membrane sac.

Adjusting the thickness of this membrane alters the speed at which it releases semen. With semen in membranes of different thicknesses, release can be phased over about three days.

This technique has been used to secure increased conception rates at the Livestock Improvement Corporation, New Zealand. Here heat synchronisation is achieved using a progesterone-impregnated Controlled Internal Drug Release (CIDR) device. Insemination was 48 hours after CIDR removal with either encapsulated or non-encapsulated semen. Conception rates were 10% higher using the encapsulated semen.

Dr Nebal said micro-encapsulated semen could also ensure all eggs of superovulated cows are fertilised with one insemination.

"Once weve determined her length of ovulation it would be possible to design a capsule to cover that period," said Dr Nebal. He suggested the technique could be available commercially for use with donor cows or synchronised cattle within two years.

Dr Nebal:"Sperm is ready to fertilise the egg over a longer period."