14 September 2001

SEXEDSEMENTRIALS are coming good…

By Marianne Curtis

SEXED semen trials on commercial dairy units reveal that, in 70% of cases, conception rates are at least as good as with conventional semen.

Cattle breeding company, Cogent has been monitoring conception rates in 100 dairy herd which used more than 20 straws of sexed semen last autumn and winter. When used in heifers, 67% of producers interviewed said conception rates were similar to or better than with ordinary semen, according to Cogents director of member services Wes Bluhm.

"For cows, 73% of producers reported similar or better conception rates, even though the technique is primarily recommended for heifers."

Large numbers of users reported conception rates of more than 50%. Of the 30% of users reporting conception rates lower than for conventional semen, 93% intend to use sexed semen again, adds Cogent.

The technique is most successful in herds adopting a precise approach, says Mr Bluhm. "Cows in these herds are managed well before service, heat detection is tip-top and semen is stored, handled and thawed strictly according to directions.

"Insemination is conducted at the optimum time and breedings and pregnancies are recorded diligently."

However, using sexed semen is ineffective in synchronised heifers, says Mr Bluhm. "Insemination on timing, rather than observed heat, has been particularly unsuccessful. This is because synchronised animals do not come into heat at exactly the same time and as there are fewer sperm in sexed semen straws, there is less leeway for inseminating outside the optimum time."

There can also be problems where semen is not thawed correctly. Dipping a finger in water to check the temperature is inadeqate and a thermometer must be used, advises Mr Bluhm. "Water will feel much warmer to the touch in January than it does in August, so using a thermometer is the only way."

Advice on conventional semen is that straws should be thawed for eight seconds at 32C, however, longer thawing and a higher temperature are required for sexed semen, explains Mr Bluhm.

"Sexed sperm take longer to become motile than conventional sperm, so require a longer thawing period. Semen should be thawed for 40 seconds at 37C. With fewer sperm in the straw than with conventional semen, there is also less room for error."

Although advice given for handling sexed semen is different from that for conventional semen, Worcs producer Clive Gurney uses the same technique for both. "My son Andrew and I are trained DIY inseminators and treat sexed semen in the same way as ordinary semen."

In future, Mr Gurney of Abbey Court Farm, Wigmore, Leominster, Worcs, intends to inseminate all cows and heifers used to breed replacements with sexed semen. "With no market for Holstein bull calves, I was excited by the concept of using sexed semen."

Mr Gurney inseminated 11 heifers in August last year. Conception rate was 100% and the result was eight heifers and three bulls, born in April. "I was surprised by the success of the technique."

A further 20 heifers were inseminated with Crichel Principal semen. This time, conception to first service was 70% and so far 12 heifers have calved, all producing heifer calves.

Successful results to date mean breeding policy for the 270-cow herd will change. "Sexed semen means top class cows can be selected for breeding replacements. Knowing that a particular cow will throw a heifer means you are prepared to pay more to use a high quality sire. Using the best on the best is also bound to speed genetic progress."

With expansion to 300 cows in mind, currently 80% of the herd is bred back to Holstein, assuming 50% bull calves and a 20% return rate.

"I reckon, 30% replacements are needed to cover yourself. Using sexed semen, serving 150 cows with Holstein genetics would enable replacement requirements to be easily met."

With conventional semen, only about 60 cows in the herd are served with a beef sire. "Breeding fewer cows to Holstein sires would enable us to increase this number to 150. Resulting Continental cross beef calves are worth £150/each at 10-12 weeks old." &#42

Particular care is needed when thawing sexed semen straws.

Sexed semen conception rates have been high in Clive Gurneys herd.

SEXED SEMEN

&#8226 More than 50% conception.

&#8226 Commercial users confident.

&#8226 Problems with synchronised animals.