Act now to prevent losses to external parasites.
Using the right product the right way at the right time is crucial to help protect cattle and
sheep from mastitis, keratoconjunctivitis, and tick-borne diseases. Understanding what
parasite to target, knowing the correct drugs and their limitations, while also timing the
application properly, can prevent disease and avoid losses this summer.
Flies
Flies are an important parasite to control, given the role they play in spreading bacterial, viral,
and even parasitic infections. It is well known that flies can transmit mastitis-causing
pathogens between cows as well as bacteria responsible for causing pink eye in cattle [1]. On
top of this, flies facilitate the spread of the wart causing papillomavirus. Midges have the
potential to spread viruses such as Bluetongue and Schmallenberg. Sheep are also susceptible
to the above conditions but are particularly vulnerable to blowfly strike.
When it comes to controlling flies, the correct product must be used at the right time and
applied in an appropriate manner. While ivermectin-based pour-on products are licensed
against warbles and horn flies, they are not licensed for protection against nuisance flies and
midges. Products containing cypermethrin or deltamethrin should be used instead. An
example of one such product is Butox (deltamethrin). This has been shown to protect cattle
for up to 3 weeks against midges responsible for carrying both Bluetongue and
Schmallenberg [2]. It is crucial products should be applied as specified in a line or spot
application on a clean hide. Ear tags impregnated with cypermethrin are available which
provide longer protection, up to four months. Treatments should be given at the beginning
of the risk period. This is typically May to September in Ireland. However, some products may
only be effective for up to 4-6 weeks, so animals will need to be treated repeatedly
throughout the risk period. Dairy farms should ensure their teat dips contain a fly repellent,
peppermint oil is a popular inclusion for this reason.
Stockholm tar is more of a traditional method of keeping flies at bay but it must be topped up
to continue to repel flies. Garlic mineral licks have some anecdotal evidence that they help
repel flies but there are limited studies to confirm this claim.
Ticks
Ticks can cause diseases such as Redwater and Tick-Borne Fever. Animals newly introduced
to a risk area are particularly susceptible. Ticks are found in rough grazing habitats and are
active from spring to autumn. They wait on the end of grasses or rushes waving their legs to
ambush animals moving by. Reclaimed land, ditches, and rough grazing habitats are all risks
that can be avoided by appropriate land management and fencing. Flumethrin, which is found
in Bayticol, is the only licensed product for ticks and mites in cattle. It is important to dose
according to weight along the back from the front of the shoulder to the tail setting and the
treatment will need to be repeated up every fortnight while the animals are at risk.
Lice
Lice are more associated with wintertime and housing. Louse infestation causes irritation,
itching, and stress to the animal. This can result in skin damage and poor coat condition. There
is growing evidence that lice are becoming resistant to the pour-on products that we use to
control them [3]. Typically, pour-on products that contain cypermethrin or deltamethrin are
used while pour-on ivermectin-based solutions will also have an effect on lice. Reducing
stocking rates, clipping hair on backs, and applying the licensed products in the correct
manner are all ways to help manage lice.
Mites
Sheep scab is a notifiable disease caused by Psoroptes mites which leads to significant welfare
concerns given the resultant compulsive itching. These mites can live off the sheep for up to
17 days and consequently, it is very easily transmissible within and between flocks. Shared
grazing, handling equipment, and bought-in animals are all risk factors. A three-week
quarantine is a good way to mitigate risk. Sheep can be treated with dips containing
cypermethrin or diazinon or, alternatively, injectable long-acting clear wormers such as
moxidectin are recommended for use. Either way, treated sheep should be kept separate
from non-infected sheep for 14 days post-treatment. Chorioptes mites can cause mange in
cattle. This is most effectively treated with pour-on ivermectin-based products because
injectable products are generally less effective in the treatment of mange in cattle.
Summary
Understanding what products to use and when to use them, is paramount for the control of
external parasites on animals. It is essential to apply pour-on products directly to the animal’s
hide and not dirt on the hide. Environmental factors also play a significant role; for instance,
if animals are located near farmyard manure, hedges, stagnant water, or rough grazing, their
exposure to external parasites increases. Contact your vet for any questions or concerns.
References
[1] Sommer AJ, Kettner JE, Coon KL. Stable flies are bona fide carriers of mastitis-associated
bacteria. mSphere. 2024 Jul 30;9(7):e0033624. doi: 10.1128/msphere.00336-24. Epub 2024
Jun 26. PMID: 38920390; PMCID: PMC11288000.
[2] Mehlhorn H, Schmahl G, D’Haese J, Schumacher B. Butox 7.5 pour on: a deltamethrin
treatment of sheep and cattle: pilot study of killing effects on Culicoides species
(Ceratopogonidae). Parasitol Res. 2008 Feb;102(3):515-8. doi: 10.1007/s00436-007-0841-z.
Epub 2008 Jan 9. PMID: 18183424.
[3] Mckiernan, F., O’Connor, J., Minchin, W. et al. A pilot study on the prevalence of lice in Irish
beef cattle and the first Irish report of deltamethrin tolerance in Bovicola bovis. Ir Vet J 74, 20
(2021). https://doi.org/10.1186/s13620-021-00198-y
About the Author
Gareth McLoughlin BA MSc MVB Summerhill Veterinary Clinic
Gareth has worked as a large animal vet for Summerhill Veterinary Clinic in Nenagh since graduating from UCD in 2023. He has a keen interest in bovine surgery, reproduction, and is currently completing the graduate certificate in Dairy Herd Health in UCD
