Preventing Milk Fever

Do you have a foolproof strategy to stop your cows going down with milk fever after calving? With increasing yields it is estimated that up to nine percent of the national herd will be affected by milk fever to some degree each year. That is a large number of cows. It is not always easy to restrict the amount of calcium a cow has available to her in the weeks coming up to calving. Larger herds might have the facilities to house dry cows in the last three weeks before calving, but this will not be possible on every farm. Straw, maize and whole crop silage have a lower mineral content than grass silage. Grass silage does vary in its tendency to leave cows susceptible to milk fever. If you have more than one clamp it might be beneficial to have the mineral content analysed so you can choose the best one to supply the ration for the dry cows. Silage from pastures with clover will contain more minerals than grass alone.

Managing Cows at Grass

There is a strategy for reducing the risk if you have to calve the cows down when they are out at grass. In the three weeks prior to calving try to find a field that has sparse grass growth and has not had any potash applied for the past two years. Hopefully then the cows will take sufficient buffer feed to keep them safe. Maize silage or whole crop silage is best although it is acceptable to add cereals and straw as well. Ideally the calving field should not have any manure or potash fertilizer added for at least two years. It will not work so well if it is a field that has had manure stored on it of if there has been any run off of water from an overflowing slurry pit. The idea is to try and reduce the potassium levels on the grass so only straight nitrogen fertilizer should be used. There is more potassium in the stems than the leaves of the grass so try to keep the sward short for the cows close to calving. Hopefully you might be able to time the grazing by other animals or silage cuts so that the grass is short when you need it most for the higher risk cows.

Vaccinating Cows and Heifers

March is the time of the year when you can get the most benefit from boosting the immunity of your herd to leptospirosis. Vaccinations can be done at anytime depending on when the problem was first diagnosed, but boosting immunity now gives maximum protection to the cows when they first go out in the spring. This is a bacterial disease that thrives in warm damp conditions so some of your animals will not have been exposed in the winter and their defense against it will start to decline. Remember, as with all inactivated vaccines, two doses four weeks apart are needed for the initial course then a single annual booster to maintain the protection against re infection. We have a supply of automatic syringes to use with this vaccine so ask if you need a new one. The company that makes Spirovac is keen to get calves vaccinated before they first go out to graze and have a 25% discount offer on the vaccine at the moment.

Scouring Lambs

Nematodirus battus is a nematode worm that damages the small intestine of lambs and will cause the lining of the gut wall to atrophy so that nutrients cannot be absorbed properly. Like other gut parasites the worms produce eggs that are passed out onto the pasture. What makes Nematodirus so dangerous is the way the development of the eggs is held up until they have been subjected to cold winter temperatures. After a cold spell all of the eggs hatch out at once and the lambs cannot cope with this challenge. Nematodirus eggs have a characteristic shape so it is possible to diagnose the condition from a faeces sample.

Increased Risk

This year the climatic conditions are such that if we get a warm spell there will be a high risk from nematodirus. It is difficult to escape problems with Nematodirus completely. It is only pastures that were grazed with lambs last year that will be contaminated so if you can use different fields when the lambs first go out this year that will help. Lambs over two months of age are able to cope better with this disease so you might be able to keep them off the higher risk fields for a while. As soon as young lambs start scouring it is better to assume that it is Nematodirus and to worm the whole group and repeat the dose every three weeks.

Calves Also Affected

There is a further twist to the Nematodirus story as young calves can suffer in the same way as the lambs and develop a severe scour if this is the first parasite they come across when they start to graze. Affected animals respond readily to anthelmintics but by the time you realize something is happening they would have already contaminated the fields for lambs and calves next year.

Official Statistics

The BSE figures for last year have just been published and they still make worrying reading. On the one hand the numbers diagnosed from cows showing suspicious symptoms has declined to 82 from 308 cows slaughtered. The worrying thing is that 1523 animals sent as casualty animals or fallen stock have tested positive since the scheme began in July 2001. I keep looking through the published data, but I cannot determine the exact figures from fallen stock for last year, they do not seem to be available in that form. Bear in mind that for each positive diagnosis all of the cattle born on the farm or reared there for twelve months before and after the  birth of the confirmed case are traced so that their passports can be stamped as not for human consumption. They are all tested when they eventually go for slaughter. There will be more testing still when restrictions are lifted on animals born after the first of august 1996 and it might well be that further individuals and cohorts will be identified.

New Cause of Abortion

Last month I saw a ewe at the surgery who aborted triplets two weeks before the lambs were due. This was a group of ewes that were new the farm that were fully vaccinated against the clostridial diseases. The abortion was a little unusual in the way that the lambs were badly decomposed. Samples were sent to the Veterinary Laboratories Agency in Shrewsbury and at first they were unable to make a diagnosis until it was revealed that there was a rich growth of Clostridium sordellii from the stomach of one of the lambs. This is apparently the first time that this organism has been isolated from an aborted foetus.

The infection has been recognized as a cause of sudden death in sheep as the vaccines give only limited protection against it.

The ewe that aborted only survived for eight hours even though she had been given a generous dose of antibiotics. There have been no further cases from the flock and they have just started to lamb now. I would be interested to hear from you if you suspect that you might have a similar problem.