As we work in the fields at this time of year, it is a joy to see a healthy flock of sheep grazing away undisturbed. But, at the back of our minds, we must continue to go through the checklist of pasture diseases and watch for any signs of disease breakdown. Lameness, scratching and fleece loss and ill thrift will be immediately obvious.
It is interesting to note what the main causes of mortality are in any given flock. In general, with sheep less than six months of age, we find parasites to be the number one killer. Next on the list is pasteurella, with clostridial diseases coming in a strong third. Our old friend fluke brings up the rear, in a greater or lesser extent, depending on the area involved.
With more mature animals, we see the table (right), the challenges change somewhat. With animals of more than six months of age, we see acute and chronic fluke becoming the number one and two biggest killers of grazing sheep. Pneumonia comes in number three and clostridia comes in in fourth place.
So as we walk through our younger lambs we should ask, what protection have we in place against parasites? One useful management system is to graze the younger stock ahead of the older breeding ewes.
Wherever possible, firstly reserve any fresh pasture for the lambs. The adult sheep move onto that fold as the lambs finish and move onto the next block of ungrazed pasture. On lowland farms, where fields are well fenced into specific paddocks, this is easily done.
It becomes more difficult on scattered farms or where grazing is on extensive areas that are not fenced into individual fields. But even in those cases, there will be new areas coming available to the flock as the season unfolds. We just need to keep in mind that the young lambs in their first year of grazing are susceptible to parasites. Therefore, give them first grazing of any area. Pasteurella, pneumonia and clostridia are the next big causes of mortality in young grazing lambs. This brings us to our vaccination programme and choice of vaccine.
Individual farmers must always get the best advice from their own vet but we will discuss it in general terms here.
It is important to send off any samples from any cases of mortality to the lab.
There are different types of clostridia and, depending on the lab results, we may change vaccine type to cover specific threats on any one farm. The inclusion of pasteurella vaccination when protecting against clostridia is useful. Pasteurella is a completely different family of bacteria to those of black leg and pulpy kidney, but it strikes just as suddenly and with just as devastating an outcome.
The clostridia disease attacks the muscle and tissues of the internal organs. Pasteurella strikes the lung tissue but swiftly causes an acute septicaemia.
Septicaemia means toxic overload of the blood and sudden death is often the first outward sign. Hence the need for post-mortem sampling and analysis. Clostridia disease will also strike at a rapid rate and so the best advice must always be to vaccinate well in advance.
Vaccination programmes can begin as early as two weeks of age, with a booster injection at about six weeks of age. The question is often asked as to whether the second shot is necessary and the answer will always be a strong 'yes'. In order to give long-term protection of six months to a year we must give the booster shot. If the mother is vaccinated, she will give passive immunity to the lamb via the colostrum. These lambs, therefore, will not begin their vaccination until two to three months old.
The mother's programme should include a booster about one month before lambing and she must also have had two injections as an initial vaccination before that. To finish, we must ensure the young flock is adequately vaccinated against pasteurella and clostridia, and keep parasite and fluke control to a minimum this summer.
Peadar O Scanaill is a Meath-based vet and member of the Food Animal Group of Veterinary Ireland. Email: firstname.lastname@example.org or call 01 457 7976