There is a lot of misinformation out there on drenching dairy cows for gut parasites, so let us set the record straight…

Myth 1: Drenching dairy cows results in milk production increase because it kills the worms that are living off the cow’s reserves: The immune system of the cow is very good at fighting off gut parasites. A cow will hardly ever pass worms in its faeces and contaminate pasture, despite continually eating parasite eggs. So in most cases, when a cow’s immune system identifies the parasites in the gut, it kills them off. The immune system has a cost however, and takes up energy. This is where drenching is likely to have most of its effect – it gives the immune system a break and saves that small amount of energy that can then go into milk. It has also been demonstrated that cows with parasites in their stomach actually eat less – they can make them anorexic! So treating them to wipe the slate clean is likely to improve appetite, and enable a potential positive response.

Myth 2: Treating my dairy cattle does not provide any benefits: This assumption is understandable, and from some aspects correct. Treating adult dairy cows with a pour-on does not alter the reproduction or body condition of these animals. But more often than not, Eprinex treatment has resulted in a milk production response. There are numerous studies which identify a milk production response following Eprinex treatment. However, the amount reflected in milk production is very small and hard to see. So here is where you need to trust us! There have been two New Zealand studies that have identified a response of 0.03 kg MS/cow/day – 30 grams a day! On a per day basis, this is hard to comprehend. However, this effect carries on for at least 150 days after treatment – the equivalent of a minimum of 4.5 kg MS/cow for a one-off pour-on.

Myth 3: My cows are skinny because of worms: As mentioned, the adult dairy cow’s immune system is very good at fighting off worms, and is able to kill off almost all of the gut parasites it encounters. As a result, it is unlikely that your cows will be skinny due to a large worm burden, and therefore unfortunately a pour-on will do very little to help. In this situation, it is probably better to concentrate on identifying why the cows are skinny and investing in fixing that problem, rather than purchasing a pour-on treatment.

Myth 4: I should just treat the skinny and young cows: Following on from above, the drench is unlikely to affect the condition score of your cattle but will provide a milk production response. The animals that are high producing and in good condition are likely to provide you with the best response after treatment (more milk). Although it seems backwards, you will get a better return on your investment if you treat those animals that are likely to respond the best and avoid those animals that are likely to respond poorly (skinny and young).

Myth 5: All products are the same, so just use the cheapest nil milk-withhold product: This is a very common misconception about drenches but it is unfortunately incorrect. When we look at drenching products, it is not just the type of drug we care about, but also the formulation. A good example of this is the antibiotic tubes we have for dry cow and pink-eye – from the same drug company we have the exact same active antibiotic and amount of antibiotic in tubes that treat pink and eye and long-acting dry cow therapy. Yet one is active for 48-hours maximum and one for at least 35 days. Quite clearly there is a difference in the formulation of the products that goes beyond the active drug. The same happens with Eprinomectin (the active ingredient in Eprinex). So when looking at which pour-on to use, Eprinex remains the one product that has had overall positive milk production responses; the other imitations cannot claim that, so may well not be ‘cheaper’.

Myth 6: The best time to drench is around dry off: Giving cows a pour-on at, or around, dry off does not alter milk production in the following season. And although not clear cut, there have been greater responses to Eprinex in cows in early lactation, as the effect often extends right through lactation. However, cows need to have the ability to eat more. So if cows are being grazed tight behind a fence, it would be better to wait until they are opened up more and being fully fed before treating with Eprinex. As a result, September often ends up being an ideal time to treat. So in summary, treating dairy cattle with Eprinex in early lactation will often results in a good cost: benefit return. At the current payout of $6.50, treating with Eprinex will result in an approximately 6:1 return! But we still need to make sure we have the systems in place to get the biggest benefit from treating. If you want any more information on treating your cows for parasites or to investigate any other areas discussed in this article, contact your VetEnt vet for more information.

08 August 2018, 21:26
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