Chlortetracycline and Liver Fluke

February 2013 CHLORTETRACYCLINE ANTIBIOTIC POWDER IN CALF MILK REPLACER The widespread use in some parts of the UK of chlortetracycline powder (Chlorsol 50% Powder) in calf milk replacer for the control of pneumonia has come to the attention of the Veterinary Medicines Directorate (VMD), the body in charge of regulating veterinary medicines in the UK. They have reviewed their previous advice, and have now stated that:  There are no chlortetracycline veterinary medicinal products authorised for incorporation into dry calf milk replacers or for reconstitution in milk on a widespread prophylactic basis.  Chloromed 150 mg/g Oral Powder for calves is authorised for individual clinical case treatment only (not prophylactic treatment).  The use of chlortetracycline in milk replacers is contra-indicated as it is possible that the presence of polyvalent cations, such as Ca2+ and Fe3+, will cause the formation of chlortetracycline complexes and associated loss of antibiotic activity. This will lead to under-dosing, making the antibiotic less effective.  The routine use of any antibiotic is associated with the development of antimicrobial resistance, and so is not in keeping with the principles of responsible use and good management practice.  Under the Veterinary Medicine Regulations, when prescribing medicated feed, only a veterinary medicinal product authorised for incorporation into a feedingstuff (premix) may be prescribed, even under the cascade.  To quote the British Cattle Veterinary Association (BCVA) Newsletter in December 2012: “In short therefore the use of Chlorsol 50% Powder in calf milk replacer is now prohibited”. There are a number of other tetracycline products that are licensed for use in calves, and their use is recommended by the VMD. Advice for those farmers that will have to stop using chlortetracycline powder in milk for prophylactically controlling diseases in preweaning calves includes:  Investigate disease outbreaks in calves in conjunction with your vet. The most common disease problems in calves under 8 weeks old are scour and pneumonia.  Ensuring adequate colostrum intakes is critical to getting calves off to a good start. Remember the 4 “Q”s for colostrum – Quantity, Quality, Quickly and Quietly.  If more than 5% of your calves either die or need treatment, get them investigated. A full post-mortem will help establish cause of death.  Ensuring adequate ventilation (but without draughts) helps to reduce infection pressure.  Avoid mixing calves of different age groups in the same shed, as this will help circulate and maintain infectious diseases in youngstock.  Vaccination can help play a role in preventing pneumonia cases, with some products licensed in calves from 9 days of age. However they are not a “magic bullet” to solve all problems.  Monitor growth rates in youngstock to check that they are performing as expected. 1 Liver fluke – the unseen threat Following one of the wettest summers on record, it is no surprise that liver fluke outbreaks have been a big problem all over the UK. Indeed the SAC surveillance figures for the last twenty years show that diagnoses of liver fluke in cattle (blue bars) and sheep (red bars) have increased markedly. The signs of liver fluke can be very varied. Acute fluke in sheep will often lead to sudden deaths in the autumn and early winter, while chronic fluke will result in ill-thrift, poor scanning rates in ewes and poor growth rates. In cattle, chronic fluke is the more common form of disease, and will present as cows in poor body condition with characteristic “bottle jaw”. Dairy cows with fluke presenting as nonresponsive downer cows in early/peak lactation have also been described by the SAC. Liver fluke will predispose to other diseases such as Black disease (sudden death due to Clostridial disease) and Salmonella Dublin. Diagnosis of liver fluke is not straightforward, especially in the early stages of the disease:  All unexplained sudden deaths in cattle and sheep should get a full post-mortem done, as the signs of fluke damage in the liver are usually easy to spot.  Get feedback from the abattoir about any liver damage in fattening stock and culls.  Dung samples can be checked for the presence of fluke eggs by your vet. However this will only pick up chronic disease due to adult flukes, and finding fluke eggs in the vast amount of cow dung is the proverbial “needle in a haystack”. Take at least 10 samples to check.  Blood and milk tests for fluke antibody levels indicate historical infection, and can remain high for many months after infection.  Future tests in development may allow for quicker and more accurate diagnosis of fluke infection within the flock or herd.  If you suspect liver fluke in your animals, contact your vet as soon as possible to take samples for testing. There are a number of treatments for fluke on the market, which vary in their withhold times and which stages of fluke they can kill. Triclabendazole (eg. Fasinex) will kill down to 2 week immature stages, whereas nitroxynil (Trodax) and closantel (Flukiver) will only kill down to 6-8 week immature stages. If fluke has been diagnosed in your flock/herd, speak with your vet to draw up a control program:  Only albendazole (eg. Albex 10%) is currently licensed for use in milking cows in the UK, with a 60 hour withdrawal period.  Treat all cattle and sheep with a flukicide capable of removing immature and adult flukes in October and January, and again in the spring with a flukicide that removes adults.  Vaccinate all animals against Black Disease.  Treat all cows at drying off with a suitable flukicide. Note that none of the products are persistent, so as soon as the cows go back out to pasture, they may be picking up more fluke.  Resistance has been reported to triclabendazole, and if you suspect that it is not working, then contact your vet.  Take dung samples 3-4 weeks after treatment to check that the drug has worked.  Treat all incoming stock to prevent resistant fluke being brought onto the farm. 2