19 September 1997

DEVICES THAT HELP COWS GET BACK TO PREGNANCY

Two progesterone releasing devices are now available to control and manipulate oestrus cyles and reproductive problems. Cheshire vet John Dawson discusses the uses of each

WITH falling milk prices and barren cow values there has never been a more important time to maintain peak reproductive performance within the herd.

Returning the cow to the pregnant state is an important procedure which sometimes requires some artificial help. To this aim the vet has a number of hormonal tools to help control and manipulate the oestrus cycle of the lactating cow.

Progesterone is one of the hormones which is used and has been administered via a sustained release device called a PRID (progesterone releasing intrauterine device). A new device which was pioneered, tried and tested in New Zealand is also used by vets. The CIDR (controlled inter-uterine device) is a similar device, administering the same hormone via the same route, but looks very different.

The PRID coil, as the name suggests, is composed of a stainless steel, spiral device covered with an inert elastomer which contains the progesterone hormone with a soft nylon string attached for removal. The CIDR is a T-piece consisting of a nylon spine covered with a silicon elastomer which contains the progesterone; a ridged plastic string is attached for removal.

The PRID coil is loaded into a speculum which has a 3.8cm (1.5in) diameter; the CIDR is loaded into a speculum with a 2cm (0.8in) diameter. The devices are deposited in the vagina with the aid of the speculum where they remain for a predetermined period which varies depending on the condition treated. The implant doesnt need to be in the vagina, but intravaginal is least invasive and easily removed. Both are tricky to load but the narrow diameter of the CIDR speculum means it is easier to insert, making it more comfortable to use in heifers. The T-piece looks as if it should be more uncomfortable when in place but this is not the case. Both devices can cause vaginal discharge but this clears once the devise is removed and doesnt affect fertility.

PRIDs can have a tendency to fall out of big cows but this can be overcome by stretching the spiral before insertion so that its diameter is larger. CIDRs stay in place more readily as long as the stiff plastic string, used to remove the device, has been cut short so that the end is just visible at the vulva lips. If it is left protruding, it becomes a plaything for inquisitive cows which pull out the device with their tongue.

The soft nylon string of the PRID is quite long and can occasionally become wrapped round the tail as it flicks flies, and is pulled out.

It is important that the proper lubricant is used with the PRID – use a calving lubricant – and PRIDs are more prone to falling out. Any lubricant can be used with the CIDR.

Hazard for bull

The PRID coil can be a hazard for the stock bull. If the cow comes into oestrus while the device is in place, for example when someone has forgotten to remove it, the device can become lodged on the penis of a bull while serving the cow.

The inert elastomer of the PRID incorporates 1.55g of progesterone and has a gelatine capsule, containing 10mg of oestradiol benzoate attached. The capsule dissolves quickly under the influence of the vaginal fluids, releasing the oestradiol which is absorbed through the vaginal wall. The CIDR contains 1.9g of progesterone contained in the silicon elastomer. Both devices release the progesterone slowly over a period of days.

Progesterone released from both devices maintains plasma progesterone concentrations at a sufficient level to inhibit release of the pituitary gonadotrophins and so prevent onset of oestrus. This slow release of the hormone allows effective control and manipulation of the bovine oestrus cycle. This can be put to use to treat many conditions and synchronise oestrus in groups. There are many treatment protocols used by different vets which all work in a similar way, delivering a mixture of hormones resulting in effective oestrus synchrony.

Both devices can be used to help manage the seasonally calving herd with a tight calving pattern. They should not normally be used prior to 30 days after calving but they can be used in late calvers in the seasonally calving herd, gaining time to conception.

Both with equal effect

Both can be used with equal effect when treating most conditions but there are some cases where one is more beneficial. Both can also be used effectively when synchronising a group of cows or heifers for group insemination or embryo transfer. However, because it is smaller and easier to insert, vets prefer the CIDR in heifers.

If an intrauterine device is being used to treat cystic ovarian disease it can be treated more easily with a PRID as it has the capsule of oestradiol hormone attached which is needed for maximum cure rate. CIDRs need an injection of oestrogen on insertion to supply the same effect.

Both devices have been used to administer additional progesterone to help maintain pregnancy where the cow has aborted previously.

They must be removed at least six hours before an animal goes for slaughter. In addition no animal can go for slaughter during the first 24 hours after PRID insertion. Neither has a milk withdrawal period. Both devices must be disposed of carefully. &#42

The CIDR is smaller and easier to insert than the PRID, so most vets tend to prefer using it for heifers.

PROGESTERONE

RELEASING DEVICES

&#8226 PRID for cystic ovarian disease

&#8226 Smaller CIDR better for heifers

&#8226 PRIDs can fall out of bigger

cows