Top Reasons Why Your Drench Program Didn't Work

Every summer/autumn we see numerous lines of calves that have suffered poor growth rates and/or shown signs of clinical parasites.

Calves that are ‘loose’ (dirty tails) despite grazing on high dry matter feeds, ‘wormy’ smelling faeces, and coughing may be all indicators.

Here are some of the reasons why parasites may be an issue:

The drench interval was too long in the current season

  • Most worm species take 3 weeks to mature and start laying eggs. If the interval between the end of the activity period of the drench extends more than 3-4 weeks eggs and larvae will build up on pasture.

  • A key part of a drench programme is to return for next drench before worm eggs in faeces become numerous.

Product selection did not suit the situation

  • Oral drenches have no persistent activity - as do most solvent based pour-on products.

  • Where high worm pressure is suspected either reduce the drench interval, or use proven long acting pour-on products or consider drench bolus (capsules).

There was a high pre-existing worm larvae load on your pasture from the previous season, meaning calves were always being challenged.

  • Every mouthful of dry matter that is high in larvae will reduce appetite and therefore DM intake and weight gain.

  • It is important to work in with other graziers on a property to ensure everyone works together every year to keep the pasture larval load limited.

Be aware of climatic conditions

  • There is often mass emergence from dung piles after extended dry periods when the weather breaks.

  • Conversely with extended warm, wet, humid conditions, larval survival will be aided, this could increase the challenge by more than 10 times!

Vet Certification for Transport

As the mating season concludes many farms will be looking to offload bulls and start making decisions over cull cows. It is during this time we see an increased requirement for veterinary transport certificates. It is a legal requirement that animals are fit for transport. The certificate remains valid for 7 days from the date of examination and the animal must be slaughtered at the nearest processing plant.

What we need from you:

  • An area to adequately examine and restrain the animal when required

  • The animal tagged with a recordable number for identification

  • The location of the processing plant and when killing space has been booked.

From a veterinary point of view:

Due to increased scrutiny being placed on transport certificates by MPI, there is strict criteria that we as veterinarians must follow. Below are common conditions requiring certification and the associated requirements.

Penile conditions: Bulls must be able to urinate freely, not have any haemorrhage, swelling, abscessation or discharge from the area surrounding the penis.

Cancer eye: the cancer cannot be larger than a $1 coin (2cm), confined to the eye of eyelid (not spreading), not bleeding or discharging pus.

Lameness: Great emphasis is now being placed on lame animals being transported for slaughter. Lameness is scored 0-3. Grade 2 animals may be certified fit for transport with specific instructions such as reduced pen density. The link below is the Dairy NZ lameness scoring system and I strongly encourage all farmers to view the following video to assess whether the animal is a suitable candidate for certification.


Each summer we investigate several cases of calves scouring post weaning. While there are many causes of diarrhoea in weaned calves i.e. parasitic enteritis, Salmonella, and BVD, we regularly diagnose Yersinia, which is a bacteria that causes diarrhoea. We often see Yersinia ‘roll’ through a mob of calves - with a small number of calves being affected at any one time. Treatment is aimed at correcting dehydration and administration of antibiotics. Prognosis is usually good except in advanced cases.

There is circumstantial evidence that Yersinia is often associated with concurrent disease i.e. BVD, parasite burden, low trace element status - especially selenium and copper. Remember - that Yersina (both Y. pseudotuberculosis and Y. enterocolitica) are zoonotic - and hence are a common cause of food poisoning in people. Keep the hygiene standards high if you are dealing with scouring animals!

Please contact the clinic if you are concerned about ill thrift or scouring in your weaned calves.

When lame cows get out of control

We are visiting a few farms at the moment where lame cow numbers have got out of control. The smart money is on picking up a foot ASAP and correcting any lesions before they get too bad. If lame cows are left they’re likely to eat less, produce less milk, have lower repro rates, and ultimately have a greater risk of being culled.

On some farms, however, we are seeing lame cow mobs of 30-100+ cows. By this stage farmers are struggling with time, and the problem often seems insurmountable. Human nature takes over, and so these cows are often left in a close paddock under the “wait and see” treatment regime, rather than being picked up and treated. If you are in this boat, or want to avoid getting there then we have three options to help:

  • Staff Training: we can come out and teach your staff members about how to treat lame cows. This can help spread the workload across more people on farm.

  • Vets to Treat: we can send out a team of vets (if available) to treat enough cows to get the mob down to a manageable level. To enable multiple vets to work at a time these animals would need to be treated on the platform/herringbone (rather than a race). Budget on a treatment rate of around 4-6 cows per hour (per vet).

  • Healthy-Hoof Lame Cow Prevention Training: Andrew, Luke and Ryan are all trained Healthy Hoof providers and can come out on farm to teach staff about how their actions (i.e. gate use, animal handling) can increase or decrease lameness. We have had some amazing results on farms following these courses, with dramatic reductions in lameness just from a change in staff attitude and knowledge around cow handling. A more in-depth package is also available looking at diagnosing track and shed issues that are having an influence.

The hidden costs of lameness can quickly mount up, and only get worse the longer they are left. Traditionally we’ve used an industry figure of around $200 per lame cow. However DairyNZ recently proposed a figure of $500 if you have to start taking cows out of the vat. If you think your lameness issues may be spiraling out of control then give one of our vets a call and we can work out how we can best help you get back on top of the situation.

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New Calf Disease - Sporadic Bovine Encephalitis (SBE)

Two years ago a new calf disease was reported in NZ. This was first seen on several farms in the Canterbury area and then more latterly in the Manawatu. To date there have been around 15 properties that have had a confirmed diagnosis in NZ.

The disease is caused by the bacterium Chlamydia pecorum (which was first found in NZ in the goat population about 30 years ago).

Affected calves develop neurological symptoms which include seizures and hind limb ataxia (wobbly in back legs), depression and an inability to stand. The progression of the disease is quite rapid - within 24-48 hours healthy calves may no longer be able to stand or want to suckle. The spread of infection through a mob of calves seems to be quite rapid - a high percentage of calves in the mob may have high temperatures without displaying significant illness.

The brain, heart and abdominal organs can all be affected. The pathology to the heart when viewed at post-mortem can be very dramatic (see below). The pericardium (sack around the heart) is thickened and full of fibrin (see arrow).

In September we diagnosed the first case in our practice. The affected farm has lost around 20 calves out of 350 reared, but it is probable that many more would have died had treatment not been provided. Early treatment is required to be successful. The rearer’s commented that they had not realised how sick the whole mob was until they started playing again a few days post-treatment.

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