27 September 1996

Progesterone tests cut vet inspections

Skilled breeding management is vital to efficient livestock production, be it for milk or meat. This special focus starts by examining how milk, progesterone testing can improve dairy cow fertility management. Jessica Buss reports

MILK progesterone testing has halved the number of cows that need inspecting by the vet at Rangemore Farms, Staffs.

Its two 220-cow, 7600-litre herds are taking part in University of Nottingham studies on cow fertility, and are seeing some practical benefits already.

Farm manager Tony Dally says each herd block calves half the cows in spring and half in autumn.

He claims the spring calvers are hardest to get back in calf because they are turned out to grass at the start of the breeding season and their nutrition is more difficult to manage. But this year 109 spring calvers in one herd achieved a 62.4% pregnancy rate to first service, compared with rates in previous years of about 50%. "Progesterone testing is a good aid to fertility. It allows us to cull the cows we want rather than those that do not get back in calf within the correct time," he says.

Progesterone levels monitor the cows oestrous cycles, their suitability for insemination, and if they are pregnant. "Tests on the service day, five days and 24 days after service are also useful to help maintain the calving interval."

When a cow shows a succession of low and high progesterone periods, it indicates she is cycling normally and can ensure service is at the correct time. But when there are persistent low recordings she is either not cycling or cystic, he adds. Alternatively, progesterone levels could be high because she has a persistent corpus luteum or is pregnant already.

At Rangemore some cows with low progesterone at day five post-service have a progesterone-releasing device known as a CIDR (controlled internal drug release) inserted from day five to 12. This may help stimulate embryo growth to provide the hormone signals needed for the cow to maintain the pregnancy.

Mr Dally claims this can save three weeks in her breeding cycle, which is important for block-calving herds. And, a high progesterone 24 days after service shows likely pregnancy.

For these studies milk samples are taken every other day by the herdsmen and are analysed by University of Nottingham staff. "The herdsmen would not have time to take samples and use on-farm test kits that can take up to two hours to obtain results."

He hopes that an automated in-line milk progesterone test will be invented and developed soon. This could link to the parlour computer aiding the identification of the animals to serve after each milking. It would also save putting cows to the vet when oestrus is not observed when they have had silent or short heats. Taking samples between calving and service gives valuable information, says Mr Dally. Each cows progesterone must rise before it falls to indicate the cow is cycling.

When oestrus cycles are abnormal the vet sees her sooner and he can use the progesterone profiles to support his diagnosis.

Progesterone profile patterns and the level at which progesterone peaks is an indicator of the chance of pregnancy. When profiles seem abnormal or the peak is low, cheap semen can be used, says Mr Dally, so allowing higher genetic, more expensive semen to be used when pregnancy is more likely.

Pre-service milk progesterone testing means that usually fewer cows need checking for bulling each night. These cows can also easily be checked for low milk yield or abnormal behaviour which may indicate bulling.

In one study some cows are being induced into oestrus early. "If a cow starts cycling in the first 21 days after calving it is thought she will have stronger heats and improved conception rate."

Cows in the study are given prostaglandin 12 days after calving to ensure they are clean, and two days later CIDRs are used to maintain an early oestrus cycle. This allows more cycles before service. But as a control some cows must be allowed to come into oestrous naturally or left until 80 days after calving before vet intervention. &#42


PROGESTERONE SIGNS


&#8226 Cow is ready for service.

&#8226 Silent or short heats.

&#8226 Early pregnancy diagnosis.


Progesterone is the hormone produced by the cows ovaries and the placenta. The progesterone level in milk is high when the cow has a corpus luteum (a structure on the ovary that releases progesterone) or is pregnant. When the cow is in oestrus the level drops suddenly. It is also low after calving or at other times when the cows ovaries are inactive.

Farm manager Tony Dally… When progesterone profiles seem abnormal or the peak is low cheap semen can be used.

Cows with low progesterone at day five post-service have a CIDR inserted from day five to 12 to help maintain the pregnancy.

Herdsman Alan Coxon takes milk samples for progesterone testing to aid fertility management.