Your calves are the future of your herd so growing them to reach their potential is important. In our pasture-based systems parasitism is a major factor that can knock back growth rates once calves are weaned and on grass. In the past, our advice has been to regularly drench calves to combat this. Unfortunately, the parasites have caught up! We are increasingly seeing the development of resistance, and subsequent drench breakdown, on properties rearing youngstock.
This means we are having to ‘reinvent the wheel’ so to speak when it comes to protecting our youngstock from parasitism. The use of drenching needs to be reserved for only when it is absolutely necessary, leaning on other management techniques to minimise the impacts of parasitism in these animals.
One cornerstone of this approach is increasing the amount of monitoring through faecal egg counts (FECs).
FECs can be utilised in two ways:
- To monitor the parasite burden to inform our drenching decisions. This involves collecting faecal samples when you believe calves are due a drench. Samples can be taken from individual calves or as a pooled sample (discuss with your vet which strategy is best for your farm). The number of eggs seen in each sample can then be used as a proxy for parasite burden, and in combination with other factors (i.e. general health, condition, feed availability) we can decide on whether drenching is necessary. In many cases, we can lengthen drench intervals and reduce the amount of drench used on farm.
- To monitor the development of any drench resistance. If drenching is effective, parasite eggs should be absent from faeces following drenching. Collecting faecal samples 10-14 days post drenching to check this, is a good initial step to monitor for any resistance that may be developing on your farm. If eggs are present in these samples, your vet may recommend further testing in the form of a Drench Check or Faecal Egg Count Reduction Test so that the current efficacy of the drench can be calculated and to identify which actives may be failing. Drench efficacy must fall below 60% before we see signs of resistance clinically. Regular monitoring allows us to identify issues earlier when things can be more easily turned around before we deal with full-blown drench failure.
As alluded to above, responsible drenching is only one piece of the puzzle when it comes to managing parasitism on your farm. Reducing exposure to parasites by managing pasture contamination, and ensuring calves are in good health and well-fed to start building their immunity, are also important factors. As we head into the warmer months, and as calves transition from milk to pasture, now is a good time to start monitoring what the parasites are doing on your farm. This is also the time of year when vets/techs are regularly on farm for the likes of vaccination and weighing visits, presenting good opportunities to collect samples at the same time.
Dr Steph Reid, BVSc, BSc (Hons)
