22 November 1996

GOOD FERTILITY GAUGE

Submission rates are a useful way to gauge herd fertility trends. Jessica Buss reports

KEEPING on top of herd fertility depends on monitoring the number of eligible animals put forward for service in a 24-day period.

This submission rate is often forgotten, says Cogent vet Stewart Scott, yet it gives the quickest indicator of herd fertility trends.

Pregnancy rates are too slow to analyse herd fertility, he says. And even pregnancy scanning cows at 30 days is too historic to identify and solve poor fertility.

"Submission rates show whether nutrition, cow health and observation are good or poor." His targets for submission rates are 85% for heifers at Cogents embryo recipient unit and 75% for the 1000-cows on the Grosvenor Farms, Aldford, Cheshire.

Fertility management is high on the agenda for these animals, all of which may be used as Cogent embryo recipients. Pregnancy rates on three of the five Grosvenor herds are now above 65%, but Mr Scotts target for the herds is 75%.

High submission rates hinge on cows showing signs of bulling and on good observation. Specific heat observation periods of 20min three times each day are needed.

"Observations must be when stock are settled – not feeding," says Mr Scott. "Before morning milking when the main lights are off and cows are lying down is not a good time to see them bulling. Options are different from farm to farm, but it is important to establish a routine for you and for the animals."

Good records are also essential to monitor fertility accurately. For submission rates keep a sheet of eligible animals numbers and then cross them off when they show heats, he advises. Computerised systems may be helpful. And heat detection aids such as tail paint can assist observations.

Ideally all cows should show signs of first heat within 30 days of calving – in practice expect to see at least 50%. At Grosvenor, cows not showing heats within 30 days are examined by Mr Scott and treated promptly.

"The time of first heat after calving is a direct effect of dry period feeding and trace elements supply," he says. "When a cow shows a heat soon after calving the uterus becomes smaller. The more heats she has before service the smaller the uterus becomes." The smaller uterus helps the fertilised embryo send its signal to the cow to maintain the pregnancy.

When the submission rate is low ask why, stresses Mr Scott. When heat observation is known to be good then consider why cows are not bulling. Useful fertility indicators are nutrition, lameness and mastitis incidence, stress, health of calves, ease of AI, strength of heats and intervals between heats.

According to Grosvenor Farms dairy manager John Mogg attention to nutrition for good fertility starts at drying off. Cows must be dried off in the correct condition and fed minerals before calving.

In early lactation the diet energy balance must keep weight and body condition losses to a minimum, says Mr Mogg.

Mr Scott adds that negative changes to nutrition up until eight weeks after service can be detrimental to fertility. But positive ration changes may aid fertility.

This was demonstrated recently on the Grosvenor units when submission rates increased after introducing of maize-based rations which improved the diet energy density.

Mr Scott also believes that clipping the backs of hairy animals may improve fertility; it keeps them cooler so encourages higher feed intakes.

Trace minerals also have an important role, he claims. Poor health of young calves shortly after birth and low activity of cows seen in heat can indicate a trace element deficiency.

Although blood profiles and forage tests pinpoint major deficiencies of minerals they are only a rough guide. Ideally the mineral balance in the pre-calving ration should be correct. But Mr Scott believes that for top fertility performance giving a trace element drench a few weeks before embryo transfer or service is worthwhile. Cows are drenched before calving to ensure the calf is healthy and viable.

Further doses of the drench are given when cows suffer difficult calvings, or ill-health such as lameness or mastitis, and when cows are slow to show heats.

"We are using trace elements in place of prostaglandin injections to improve fertility," he says.

Reduced fertility can also occur after stress such as social changes. Group changes should be avoided until animals are eight weeks pregnant.

Lighting may also affect fertility but there is little evidence for this, he says. A long period of light is good for milk production, but a period of low light could reduce stress.

"Suppressing lighting at night could discourage cows from displaying heats at night when they are not observed," says Mr Scott.n

Even early pregnancy diagnosis by scanning is too historic to monitor fertility, says Stewart Scott. Submission rate gives the quickest guide.


IMPROVED FERTILITY


&#8226 Give extra trace elements.

&#8226 Clip the backs of hairy animals.

&#8226 Monitor submission rates.

&#8226 Avoid stress.

Good observation ensures high submission rates at the embryo recipient unit.