Over the next few months, thousands of 100kg Friesian bulls and dairy beef calves will move from rearers to beef traders and finishers.
Wormwise manager Ginny Dodunski warns about unwanted passengers.
It’s well known that 100kg calves need good facilities and careful management to thrive through this transition.
However, what’s less well understood is the risk these calves present to the receiving property. Depending on the source, they may be bringing some pretty nasty worms with them.
It is not uncommon for calves from intensive rearing properties to have had two to three drenches prior to leaving the rearer, especially later batches of calves which are more likely to include slow growers.
It is now common on intensive cattle properties, for worms to be resistant to double and triple combination drenches. Calves from these properties can be carrying a high proportion of resistant worms.
One hundred kilogram calves are yet to develop effective immunity to fight off parasites. They are little worm factories, churning out lots of worm eggs that then develop into infective larvae on pastures.
If the calves you’re buying have a high proportion of drench-resistant worms on board, you can be setting yourself up for problems - both with calf performance this season, and in the longer term as their drench-resistant worms multiply up on your block.
So how to prevent this from happening?
The first step is a conversation with the rearer. If no, or little worm drenching is taking place, the risk of importing resistance is probably low.
You can also ask the rearer for recent drench testing data to see if the common drench classes are effective. If this data is not available, or drench resistance is present, then a quarantine drenching protocol is necessary.
Having an effective quarantine protocol in place minimises the risk of importing drench resistant worms.
What does an effective quarantine protocol look like?
An effective quarantine protocol includes:
- A drench (or combination of drenches) that is most likely to remove combination-resistant worms.
- A stand-down time, where eggs not killed by the drench, drop out onto an area of ground where they cannot develop into larvae and complete their life cycle.
An effective quarantine drench
Combination drench resistance is increasing sharply in cattle worms in New Zealand – therefore the most appropriate quarantine option is to use a ‘novel’ drench - containing the actives Monepantel (Zolvix®) or Derquantel (Startect®). Of the two novel drenches available in New Zealand, only Zolvix® is registered for cattle.
Zolvix®, along with many other common cattle drenches contains the drug abamectin. Abamectin can be toxic in small calves, and these products are not recommended for calves less than 100kg. It’s therefore important to set the standard for the calves you are receiving – there are several good reasons for a ‘no calves under 100kg’ policy - the ability to administer an effective quarantine treatment is one of them!
The efficacy of a drench is determined not only by the active ingredients, but also the volume given and technique used. Calibrate the drench gun, weigh some calves and drench to the heaviest, ensuring the whole dose is given to each animal. If there is substantial variation in weight, draft the calves into heavy and light lines to avoid overdosing.
Another risk factor for overdosing calves with abamectin is the ‘oesophageal groove reflex’. This occurs when nerves in the back of a calf’s mouth sense that liquid is present, causing its oesophageal grove to close and direct the liquid straight into the abomasum. Drench is designed to go into the rumen, from where it is absorbed more slowly. Absorption of abamectin from the abomasum can cause toxicity. This is more likely when calves are still on milk, or very recently weaned off milk. Check that the calves you are buying have been weaned off milk for more than a few days.
Stand-down time
New arrivals need to be held in a grass-free area, with feed and water for 24-48 hours, as eggs inside the calves’ guts pass out - eggs are not killed by drench. Larvae that emerge from eggs on these areas mostly die, as they need grass to live on.
Another option is for new calves to be held in a specific quarantine paddock for 24-48 hours. This area must remain calf-free for many months afterwards, ideally being grazed by sheep, deer or adult cattle, who can remove any resistant larvae that have developed. The paddock could also be earmarked for a spring-sown crop. If many batches of calves are arriving, this system is hard to run - how many ‘calf free’ paddocks can you afford to have after the quarantine of each batch?
Management after quarantine
It is safest to graze new arrivals on paddocks that are likely to have some cattle worm larvae on them - ‘just in case’ any worms survive your quarantine drench. Grazing this type of pasture ensures that any such worms are well diluted out by incoming larvae from your pastures, rather than remaining as a pure drench- resistant population inside the calves.
Allow calves the best pick of grass (use other stock to maintain pasture quality) and continue to feed meal or other high energy supplement - to take care of the ‘Feeding’ aspect, which is the most important worm management strategy of all. Good luck with your calves this year - check out the Wormwise pages on the B+LNZ website for more worm management information.