27 September 1996

ET costs minimal against lost lactation

Infertility is the biggest single reason for culling dairy cows. But some of those cows could be saved using a new direct ET technique for repeat breeders.

Jessica Buss reports

INFERTILE cows can be treated successfully using embryo transfer with a potential 63% pregnancy rate.

So says Wilts dairy vet Peter May, who has been testing the technique of implanting two beef embryos to treat repeat breeders on-farm.

He achieved the 63% success rate in 19 animals into which he transferred embryos seven days after service. A further 31 animals had embryos implanted seven days after they were bulling but without serving them; the pregnancy rate was 48%.

The cost of two beef embryos and transfer is £85. "This is little compared with the value of the cows next lactation," says Mr May. "With stock prices at their current low value it must be a good cow to consider treatment."

But if the difference between purchases and cull cows was £500 the cost benefit could be £780 if DAISY, University of Reading study figures are used, he adds.

"Cows treated with ET had been served three or four times and run with a bull but failed to get in calf. Typically, these were younger animals that were cycling regularly and did not appear dirty.

"One reason for this infertility is that the egg or sperm is not getting up the fallopian tube, so cannot be fertilised or she may release the egg too late." When an embryo is transferred it bypasses the fertilisation process.

The optimum time for ET is seven days after oestrus but there is at least a 24-hour window that gives some flexibility, he claims.

Before transfer the cows are examined using an ultrasound scanner to check they are cycling normally. This also shows if she is dirty and if so she can be washed out saving on the cost of ET.

Mr May transfers two, in vitro fertilised, embryos in one straw. These are produced after collecting eggs from slaughtered cows ovaries. These are cheaper than buying purebred embryos. It is thought that two embryos send a stronger signal than one embryo to tell the mother she is pregnant, he says.

Embryos are frozen in ethylene glycol for one-step thawing. This makes the process similar to AI and simpler than conventional ET, in which the embryo needs several washes under a microscope.

Embryos transferred after natural service may give better conception rates than from synchronised heats, claims Mr May. And by working from natural heats the vet has seven days warning.

"I was worried about getting triplets when implants were after AI," he says. "The 12 cows in calf after ET and AI were scanned and none are carrying triplets. However, five have twins." But scanning can identify the twins so these cows can be managed more effectively in the dry period, he adds.

&#8226 Mr May will soon have trained 63 vets in ET with Dick James from Sefax and John Dawson from North-west Embryo Transfer. Mr May has been encouraged by AI company Semex which is keen to use vets for pedigree ET and he hopes commercial producers will in turn use their vets for direct ET.n


&#8226 Suitable for cows that have returned three times.

&#8226 Possibility of over 60% conception rate.

&#8226 Low cost at £85 a cow.

Vet Peter May using embryo transfer to treat infertile cows in James and Jane Woolfords herd.