Worms in cattle
As the winter approaches and cattle are being housed and dosed, it is important to use the correct product to prevent Type II Ostertagiasis.
Any worm larvae eaten after September do not go through normal development. These larvae enter the glands in the stomach, where they remain dormant over the winter. These are known as inhibited larvae. In incorrectly dosed animals, thousands of these inhibited larvae simultaneously develop to adults and emerge from these glands in early spring. As a result there is severe damage to the gut, which often results in death. This disease is called Type II Ostertagiasis, compared with Type I disease which occurs in calves and young stock at grass during the summer and autumn.
Signs of Type II disease include: Profuse, watery diarrhoea, rapid weight loss and death. This is usually seen in February / March.
Prevention: In order to prevent this type of the disease, it is essential to drench the animals at housing with an anthelminthic which must be effective against these inhibited larvae. Avermectins are very effective, some Benzimidazoles may be effective, but not Levamisole which is ineffective and should not be used.
Anthelmintics can be divided into three separate groups. It is important to know which of these groups the drug belongs to since the dosing interval, and the type of worms that this product may be effective against will differ between different types. Benzimidazoles are more commonly know as the white drenches, Imidazothiazoles or Levamisole based products are the clear drenches and Avermectins are the new generation products such as Ivomec, Cydectin and Dectomax.
Benzimidazoles: This group of drenches has been on the market for a long time. There are many different types. Some will kill adults and larvae but others will not kill inhibited larvae. In general they are very safe products but some can not be used in pregnant animals. Some may also kill fluke and tapeworms at a higher dose rate.
The chemical is slowly eliminated from the body, which gives it a long withholding time.
Levamisole: This drug acts by paralysing the worms. Correct dosing technique is required to prevent accidental overdosing which can cause nervous signs. These products are only effective against 70-80 percentage of worms and it has no effect on inhibited larvae. They can not be used for animals at housing. It is quickly eliminated from the body so it has a short withdrawal period.
Avermectins: This group of chemicals is highly effective against all types of worms. They will also kill mange mites and most type of lice. A flukicide may be included but this only is effective against adult fluke. These drugs persist in the body for weeks after treatment, thus reducing the dosing frequency.
Resistance to Anthelmintics is an increasing problem in sheep. If resistance occurs against a wormer, it occurs against all the wormers in that category. Worms that become resistant pass this resistance on to its offspring. Several factors may predispose to resistance. These include under dosing, too frequent dosing and purchasing sheep with a resistant worm burden. There have been some cases of worms being resistant to Ivermectin in England and New Zealand
Fluke disease in Cattle:
In cattle, mature fluke living in the bile ducts of the liver are the main cause of disease. This prevents the liver from functioning properly. These mature fluke are present in the bile ducts from December onwards.
The signs of fluke disease are due to liver damage: Cattle are thin, not thriving, with a poor coat, and bottle-jaw. This is a swelling under the jaw of the affected animal. Fluke eggs may be present in the dung of animals that are chronically infected.
Fluke control: Housed cattle Anthelminthics:
There are a variety of different anthelmintics on the market for control of fluke in both cattle and sheep. Knowledge of these products and their range of action are essential for effective disease prevention.
- Triclabendazole (Fasinex) - This is effective against all ages of fluke, killing both adult and developing fluke. As a result of its wide range of action, treating the animals will result in a near total fluke kill. Animals should be dosed shortly after housing.
- Nitroxynil (Trodax) - This is an injection, which may cause lumps at injection site. It has activity against adult and some activity against young fluke to two weeks of age. For best results, it is best to wait until all possible infective stages of the fluke are older than two weeks before treatment. Therefore, inject animals two weeks after housing or if used in dairy cows, at drying off.
- Closantel (Flukiver)- This product kills immature fluke from five weeks. Therefore dose animals five weeks after housing to achieve a complete fluke "kill".
- Other drugs may only kill adult fluke from 12 weeks. They are of no use in the prevention of acute disease outbreak, which is generally caused by young fluke. These products are best used where the risk of disease and fluke infection is low. Dose animals in January (12 weeks after housing) after all stages of fluke have reached adulthood to achieve a complete fluke "kill". There is a degree of risk with the strategy. An alternative would be to dose once to kill all adults, and then to wait for a while until the remaining fluke have reached adulthood and dose again.
Fluke control in out wintered cattle:
- Dose in January (remember these cattle will have been taking in fluke all winter, so all stages of fluke will be present in their liver in January). If drug only kills adults then repeat in March and April.
- On land where fluke infestations are likely to be high, another dose of Triclabendazole in September/October will be of benefit.
If there is a warm and wet June / July, the Fluke Forecast can be used to predict the level of disease.
Combined Fluke and Worm Products.
There are a wide variety of combined fluke and worm products on the market. Great care must be taken when using these products since they may not be the best product to use at certain times of the year. Some things to look our for are:
- When dosing at housing with a combined product, make sure that the worm portion kills inhibited larvae. It should say this on the pack. Levamasole and some Benzimidazole products are of no use at this time of year.
- Check what stage of fluke the flukicide portion kills. If it only kills adult fluke, you may have to wait until December to have a complete fluke kill, or have to treat at housing and repeat later in the winter.
- Treating young stock at grass with some combined fluke and worm products has a limited value when treating for fluke since there are no adult fluke present in these animals at this time of year.
- Always check the dose rate for combined products. They may kill worms but only adult fluke, and at three times the recommended dose rate for worms. They may not be economical.