Winter and spring parasite management in R1 cattle

Susceptibility to parasites and drenching frequency 

How susceptible young cattle in the 9–15 month age group are to internal parasitism is very much a function of their maturity and nutrition. We also know there is plenty of genetic variation in cattle with regards to how quickly they develop a robust immunity to parasites. This aspect is yet to be exploited commercially in New Zealand. 

Heavy, well-grown weaners with good feeding conditions are less affected by parasites than those that have grown poorly or are under nutritional stress. For instance, a 220kg beef weaner might need only one worm treatment at weaning, another in spring, and then be set for life.  

In contrast, an artificially-reared dairy cross weaner on a slow-growth pasture system might need up to nine drenches before its first birthday and still remain prone to parasitism if unmonitored. This scenario also raises the risk of drench-resistant worms developing as the season progresses. 

High-performing dairy heifer systems with abundant new grass, hay and silage often  drench monthly whether it is needed or not. This is often a waste of money and increases the risk of breeding drench-resistant worms. 

The system matters! High-feed, low-grazing-pressure R1 systems require less drenching. Growing calves as quickly as possible through the ‘window of susceptibility’ to worms is a great policy. Energy and protein matter in the fight against worms and putting calves back on supplement/pellets when the season goes against you is a good move, as is looking at forages other than grass for those artificially reared ones in the early months after weaning. 

The other thing we need to consider is which worm/s we’re most likely to be dealing with. In simple terms, there are two main worms we worry about in weaners in winter – the intestinal worm Cooperia, and the stomach worm Ostertagia. 

Those big, well grown beef weaners can have developed substantial immunity to Cooperia by nine months of age. In contrast, 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 manage without treatment, or only treat the weaker animals. 

Drench choices and resistance management 

When choosing drenches, treatments for Cooperia should contain levamisole, while those for Ostertagia should include a drench from the mectin family. Due to the growing issue of drench resistance in NZ, no treatment is foolproof. Regular drench checks, such as faecal egg counts 10-14 days after treatment, are essential to ensure the drench programme is effective. 

There is no single monitoring action to determine treatment needs for this age group. Monthly drenching is generally excessive except in the worst cases of small cattle on short feed. Typically, drench intervals can be extended in winter. Faecal egg counts can guide treatment needs, though low counts don't always mean no parasites. Low liveweight gain might indicate parasitism, but it can also result from underfeeding, which often accompanies increased susceptibility to worms. 

Effective parasite management in R1 cattle requires considering the whole picture—calf age, size, and feed quality. Part-mob treatment or drafting into stronger and weaker lines and treating only the poorer ones can be practical strategies. Tailoring approaches to specific conditions and regular monitoring are crucial for maintaining cattle health and productivity. 

Find out more

For more information on parasite management, see the Wormwise section of our website.