Cattle often get a drench in the springtime, but this may not be necessary for all animals. Wormwise consultant and vet Mary Bowron explains the variables that need to be taken into consideration.
These include their level of immunity, the level of nutrition available, and the amount of worm contamination on the pasture they are grazing.
Immunity
Most cattle develop reasonable immunity to parasites around 12-18 months of age. But how solid this immunity is, depends on a few things.
Well-conditioned cattle at or above target body weights with optimal grazing (residuals of 1500kg DM/ha or more) are better able to cope with parasites. Their poorly grown mates that haven’t been fed so well over the winter won’t be able to cope as well.
For example, a well-grown, cow-reared R1 weaned at 250kgs at 6-8 months of age, may only need a drench at weaning, one in the spring and that will be them for life.
On the other hand, an artificially reared yearling, weaned around 100kgs, grazing highly contaminated pasture won’t be quite as robust. To support their growth, multiple drenches may have been given, but if behind their target weights, their capacity for coping with parasites may be a lot less and they may still need further treatments.
Feeding
Animals provided with plenty of protein and energy are better able to fight the parasite battle than animals under nutritional stress. Depending on the time of the year, permanent pasture may not always provide enough dry matter, energy and protein for fast-growing R1’s who are also developing their parasite immunity. Alternative forages or supplements can ensure they continue to thrive.
Avoiding the worms
To ensure cattle grow well in their first year, the farm system needs to be set up to avoid a monoculture of young stock. Calves rotating year on year on permanent pasture is a recipe for disaster. Each season the larval challenge keeps building to a point where the worm burden may become overwhelming.
Integrated grazing with older cattle classes, or other species, helps prevent this issue. Cropping and re-grassing also adds extra lower worm contamination grazing into the mix. What worms are we targeting?
For their first autumn/winter the main species of worm we really need to worry about are the intestinal worm Cooperia, and the stomach worm Ostertagia.
Well grown beef weaners are likely to have developed substantial immunity to Cooperia by nine months of age. However, the poorer calf that has grown slowly since birth can still be susceptible to this worm at 12-15 months.
Immunity to Ostertagia takes longer to develop. Even R2 and adult cattle can be affected if they have been under nutritional pressure. This worm can pause its development in the stomach lining and resume its life cycle later, leading to poor growth that may respond to drenching.
This is why many advisors recommend routine treatment of yearling cattle wintered on pasture to eliminate Ostertagia and maximise spring feed benefits. However, some farms achieve very good performance without treatment, or by only treating the smaller or slower-growing animals.
When choosing drenches, treatments for Cooperia should contain levamisole, while those for Ostertagia should include a drench from the mectin family. Drench resistance is common however, and regular drench checks, (faecal egg counts 10-14 days after treatment), are essential to ensure the drench programme is effective. Though it’s better to do these on calves, as explained below.
Monitoring can help
Faecal egg counts can be useful in calves, but interpreting faecal egg count results for cattle is not as straight forward as it is for sheep. A low number doesn’t necessarily mean no worms, especially in yearlings and older cattle.
Therefore, regular monitoring of growth rates is also important. Monitoring individual growth rates can allow for targeted selective drenching of under-performing animals. This not only not only lowers drench usage but ensures refugia is provided by the untreated animals as well.
Parasite treatment of adult cattle is seldom needed, unless they are under nutritional stress. Other diseases such as BVD or Johnes can cause ill thriftiness as well, it’s not always parasites.
Well fed, well-conditioned cattle coming out of the winter may not need a drench. Weigh up the evidence and maybe you could save some money and time by not drenching.