Control flies before they impact onto productivity

Fly Control Cattle Its Your Field

Aurelie Moralis
DVM Cert DHH MRCVS, Marketing and Technical Manager, Zoetis Ireland

Flies are not only an irritant for cows and farmers alike, they also affect cow productivity – reducing how much animals graze and therefore affecting milk yields and growth rates as well as behaviour in the milking parlour.

By the time you notice cattle or sheep being troubled by flies, a population explosion is already taking place. However, it’s easy and cheap to make some fly traps (Figure 1), and then keep an eye on them every few days for an early warning that fly numbers are on the rise. You need to choose suitable bait for the flies you wish to trap, for example offal, such as raw liver is suitable bait for the fly species that bother livestock.

As soon as you start seeing flies in the trap, then you know they are going to be bothering stock and you will need to take appropriate action.

How to create a fly trap?

1. Take a two-litre plastic bottle and cut the top third of the bottle off.

2. Make some small holes in the end of the plastic bottle in order to allow rainwater to escape.

3. Invert the top of the bottle into the remainder of the two-litre bottle and seal it with clips/paper clamps to fasten it in place.

4. Place the bait, which can be made up of dog food, or an offal-based product in the bottom of the bottle.

5. Hang the bottle on a fence or gate post by fixing string to the paper clamps attached to the bottle

Fig 1. Creating a DIY Fly Trap

When to start with fly control?

If you wait until fly populations are already established and then try to tackle them, you’re unlikely to win the battle. An early start to controlling insects around livestock gives the best chance of minimising the annual population explosion of flies and midges that begins as soon as average daytime temperatures reach 10°C (Figure 2).

Fig 2. Increase in population of different flies

Winter frosts can help reduce the coming summer’s insect populations. However, even if air temperatures are below zero for several days running, the larvae of some species relevant to livestock typically over-winter about 10 centimetres below the soil surface where frost may not penetrate, so this cannot be relied upon to kill insect larvae.

Moreover, larvae of some species over-winter in woodland litter, where frost penetration is quite rare no matter how cold the weather. Then as soon as they hatch from pasture or woodland, blood-sucking species can migrate several kilometres to find livestock on which to feed.

Fig 3. Open Dung Heaps

While farmers cannot eliminate insect breeding sites from pasture and woodland, a meaningful impact around farm buildings is possible by minimising open dung heaps (Figure 3), slurry puddles, and old hay and straw stacks.

For maximum control, action must start before the insect breeding season; waiting until insects are bothering livestock allows breeding populations to become established and difficult to get on top of.

Welfare impact of poor fly control

Flies don’t only annoy cattle and sheep; they can cause major economic production losses through reduced feed intake which impacts productivity. Studies in cattle have shown, the production loss caused by flies can be up to 0.3kg a day growth rate loss and up to 0.5l a day in milk loss1.

Flies attack and feed on cattle and other animals. This causes irritation and can be involved in the transmission of diseases such as pink eye and summer mastitis. Midges also spread viruses that cause diseases such as Bluetongue and Schmallenberg. Blowflies are important due to the damage caused by their maggot stages.

Treatment options

In conjunction with good farmstead hygiene, residual pour-on pyrethroid treatments such as deltamethrin (e.g. Fly & Lice Spot On™) are licensed to control insects for up to eight weeks depending on species and population. To keep nuisance flies at bay Fly & Lice Spot On should be used monthly in cattle. There is a zero milk withhold period and so Spot On can be used in pregnant and lactating dairy cows.

In sheep it is licensed to treat established blowfly strike and a single application directly onto the maggot infested area as soon as fly strike is seen will ensure blowfly larvae are killed rapidly. In the case of more advanced strike lesions it is advisable to clip out the stained wool before the treatment is applied. The active ingredient has proven activity against midges.

Alternatively, in cattle a long acting cypermethrin (Flectron® Fly Tags) is available giving season-long fly control from a single tag. Flectron Fly Tags can control flies for up to 4 months. For maximum benefit they should be applied at the beginning of the season and all animals in the herd should be tagged.

Successful fly control starts now, so now is the time to engage farmers and ensure plans are in place ahead of the season.

REFERENCES

1. Jonsson et al (1999). Med. Vet. Entomology 13, p372-376.

Fly and Lice Spot On™ Insecticide contains deltamethrin 1% w/v. Flectron® Fly Tags 935 mg contains Cypermethrin. Legal Category LM. For further information please contact or Zoetis, 2nd Floor, Building 10, Cherrywood Business Park, Loughlinstown, Co. Dublin D18 T3Y1. (01) 2569800 or www.zoetis.ie. Use medicines responsibly (www.apha.ie). ZT/21/16/1

Key considerations for Early Season worming strategies in cattle

Maura Langan
Norbrook Veterinary Advisor

When cattle are first turned out, they should be free from parasites and do not need treatment immediately. However, in Ireland’s grass-based system, it is inevitable cattle will be exposed to worms. As part of the industry-wide goal to reduce the threat of parasitic resistance, we look at some of the factors to be considered when looking at anthelmintic treatment regimes.

Risk Periods for parasites

There are two groups of roundworms which affect cattle: gastrointestinal (GI) worms, of which Ostertagia ostertagi and Cooperia oncophora are considered the most economically important, and lungworm, Dictyocaulus viviparous.

Both Ostertagia and Cooperia cause parasitic gastroenteritis (PGE). At turnout overwintered infective L3 larvae may be present on pasture grazed by cattle the previous season. As they ingest the larvae, cattle acquire low level worm burdens that complete their lifecycle, becoming egg laying adults. In turn these worms serve to further contaminate the pasture with eggs.

As pasture contamination builds up and warmer temperatures support the faster development of worm larvae on pasture, the risk of disease increases throughout the summer. As a result, the two peak periods of risk are 3-4 weeks post turnout and then again in July.

Exposure to low levels of gutworms over successive grazing seasons allows immunity to develop, meaning that adult cattle are less likely to suffer clinical disease. Immunity to Cooperia occurs during the first grazing season, but it may take up to the end of the second grazing season for immunity to Ostertagia to be established. Heavy infections can reduce performance significantly with losses in a severe outbreak of osterstagiosis reaching €120/head.

Lungworm in comparison to gutworm is an unpredictable disease process that affects both young animals and adults. Young stock that are exposed to lungworm develop immunity relatively quickly, however the persistency of that immunity varies. While immunity against the maturation of the lungworm larvae in the lungs persists quite well, immunity to reinfection with lungworm larvae wanes rapidly. Naïve cattle or those with poorly developed immunity to reinfection may develop severe respiratory signs when exposed to heavy lungworm larval challenge from pasture. This can occur throughout the grazing period with reports of lungworm infections as early as May in some instances. However it is most commonly seen in mid-summer and at times when heavy rainfall follows a dry spell.

Lungworm causes coughing and laboured breathing and if left untreated can result in death or long-term debility. Lungworm in growing cattle can incur losses of between €60 and €120/head.

Risk Periods for parasites

There are two groups of roundworms which affect cattle: gastrointestinal (GI) worms, of which Ostertagia ostertagi and Cooperia oncophora are considered the most economically important, and lungworm, Dictyocaulus viviparous.

Both Ostertagia and Cooperia cause parasitic gastroenteritis (PGE). At turnout overwintered infective L3 larvae may be present on pasture grazed by cattle the previous season. As they ingest the larvae, cattle acquire low level worm burdens that complete their lifecycle, becoming egg laying adults. In turn these worms serve to further contaminate the pasture with eggs.

As pasture contamination builds up and warmer temperatures support the faster development of worm larvae on pasture, the risk of disease increases throughout the summer. As a result, the two peak periods of risk are 3-4 weeks post turnout and then again in July.

Exposure to low levels of gutworms over successive grazing seasons allows immunity to develop, meaning that adult cattle are less likely to suffer clinical disease. Immunity to Cooperia occurs during the first grazing season, but it may take up to the end of the second grazing season for immunity to Ostertagia to be established. Heavy infections can reduce performance significantly with losses in a severe outbreak of osterstagiosis reaching €120/head.

Lungworm in comparison to gutworm is an unpredictable disease process that affects both young animals and adults. Young stock that are exposed to lungworm develop immunity relatively quickly, however the persistency of that immunity varies. While immunity against the maturation of the lungworm larvae in the lungs persists quite well, immunity to reinfection with lungworm larvae wanes rapidly. Naïve cattle or those with poorly developed immunity to reinfection may develop severe respiratory signs when exposed to heavy lungworm larval challenge from pasture. This can occur throughout the grazing period with reports of lungworm infections as early as May in some instances. However it is most commonly seen in mid-summer and at times when heavy rainfall follows a dry spell.

Lungworm causes coughing and laboured breathing and if left untreated can result in death or long-term debility. Lungworm in growing cattle can incur losses of between €60 and €120/head.

Farm Specific Risks

Farms with limited clean pasture (i.e. grazed by cattle in the previous season) are considered high risk, so cattle with lower immunity should be monitored carefully and a season-long worming programme established. After 3-4 weeks on pasture they will have picked up some worms, but crucially will also have been able to build up some immunity. At this point a first worm treatment may be indicated. Pasture not used by cattle in the previous year or silage aftermath is lower risk, so consider moving vulnerable groups there to avoid peak L3 larvae infection at the end of June / July. If you are in doubt as to the level of pasture contamination, faecal egg counts (FEC) 6-8 weeks post turnout will help to assess the worm burden.

FEC are also a useful tool in assessing levels of resistance to certain anthelmintics. Anthelmintic Resistance is defined as the loss of sensitivity of parasite populations to a drug that they were previously sensitive to. Essentially, this means that sensitive worms die and those that have some degree of resistance survive. The surviving worms reproduce, and their offspring then increase the percentage of the worm population carrying the resistance genes. Over time a susceptible population may be replaced by a completely resistant one. By testing dung post-treatment it is possible to gauge the effectiveness of that treatment and whether a sufficient ‘kill-rate’ has been achieved.

Herd Risks

Rather than treating frequently at set intervals, the industry is moving towards fewer treatments and only treating where necessary. Individual treatment plans should be devised for the different management groups according to level of exposure and immunity.

As we have seen, adult cattle should have acquired some level of immunity to gutworms and lungworms and should not need to be treated as often as naïve first season grazers. When considering treatment in calves, infection levels should be monitored by weighing them to determine their growth rates as well as FEC.

For second season cattle, the aim is to balance the number of treatments with performance. Growing cattle need to be allowed to build up some immunity but should never be overwhelmed with a parasitic worm burden.

Monitor regularly for lungworm: be vigilant for the first signs of coughing. Treat the whole management group at the first sign of infection to reduce the risk of long-term lung damage. Due to issues with immunity cattle of all ages can be at risk of lungworm. Herd vaccination may be appropriate and should be discussed with a veterinary practitioner.

Some worming products have ‘persistency’, meaning that they continue to protect cattle from infection after treatment. Taurador® Pour-on contains Doramectin and has persistent action against Ostertagia (35 days), Cooperia (28 days) and lungworm (42 days). This means further worming may not be necessary for another 6-8 weeks following treatment. By extending the time before and after worming, it is possible to reduce the number of doses during the grazing season.

Bought-in stock risk bringing in parasites, possibly ones that are resistant to treatment. Where possible, try to get as much information about the farm of origin and treatment history prior to purchase. Animal Health Ireland recommends treating with two different classes of wormers (either 1 BZ, 2-LV or 3-ML) and quarantining for at least 48 hours following treatment. A liver fluke treatment may also be appropriate for bought in cattle. Cattle should be grazed on ‘dirty’ pasture following treatment in order to dilute the proportion of potentially resistant worms.

On target for sustainable worm control

Sioned Timothy, Ruminant Technical Manager,
Boehringer Ingelheim Animal Health.

Sioned Timothy, Ruminant Technical Manager, Boehringer Ingelheim Animal Health.

Wormer resistance poses a threat to profitable cattle production, but there are some simple steps that you can encourage livestock farmers to take, which will improve the sustainability of worm control and safeguard the future of the cattle industry.

According to a new study, parasites are estimated to be costing the European livestock industry more than €1.8 billion per year, with cases in cattle making up the majority of this cost1. Increasing resistance to wormers is causing concern, as it makes it harder to effectively treat production-limiting worm burdens. The cost of anthelmintic resistance alone is estimated at €38 million per year1, as a result of in-production losses and treatment costs.

Treating youngstock with long-acting wormers early in the grazing season and implementing whole group treatment, rather than selectively treating a proportion of the group, are examples of strategies that may drive wormer resistance. Additionally, these approaches may impact on the ability of youngstock to develop immunity to certain parasites.

There is also an increasing focus on the ecological effect of wormers, since the presence of certain active ingredients in cattle dung can have an impact on dung-fauna, such as beetles and other insects.

Climate change is also having an impact on worm infection dynamics, which is further compounding the potential for resistance. Hotter, drier summers, reduce the survival of worm larvae, meaning that there is little or no refugia on the pasture. This intensifies the selection pressure for resistance when animals are treated.

However, infective larvae may survive in dung pats, and if released en-masse during wet weather in late summer, can cause sudden outbreaks of parasitic disease in susceptible animals.

Resistance is defined as a faecal egg count reduction of under 95% following treatment, but the benefits of treatment on production can still be seen even with FEC reductions of only 70 and 80%. It’s not until efficacy reduces to 60% or 50% that a reduction in livestock productivity becomes evident, but by then the problem is more difficult to address. 

Future alternatives to wormers

Despite the reliance on anthelmintics for worm control, there are alternatives emerging that can contribute to an integrated, sustainable approach in the future.

Vaccines are already available for lungworm, and others are in development. However, optimising immunity to worms is just one component of an integrated strategy to control parasites in a more sustainable way.

Grazing management techniques are important. Prioritising low risk pastures for the most susceptible animals, is at the core of integrated parasite control.

Other novel strategies, such as the use of mixed swards containing bioactive forage species, and certain nutraceutical feed additives are being investigated. Genetic improvements, with breeding lines selecting for resistance to worm species is also in the mix for the longer term.

None of these methods alone will control worms to a level where they no longer cause production loss, but combined with an increase in on farm monitoring, and correct, targeted use of anthelmintics when necessary, they could provide a sustainable long term solution.

Target your treatments

Using a targeted selective treatment (TST) strategy is a more sustainable method of treating worm burdens in cattle, and protecting production. It is also something that can be introduced over time, testing and refining the technique so that it works for each individual farm.

The aim with TST is to focus treatment on animals carrying significant worm burdens, avoiding whole group treatments, whilst maintaining health and productivity. This approach slows the development of resistance by allowing low numbers of worms to persist in untreated animals, so any resistant worms that survive in treated animals are diluted by this mixed population.

When targeting animals for treatment, livestock farmers should remember the 80:20 rule. Around 20% of animals carry 80% of the worms, so a proportion of healthy animals in good condition can be left untreated without adverse impact on health or productivity.

Faecal egg counts (FEC) can be used to assess worm burdens in young animals in their first few months at pasture. This becomes a poor measure of worm burden as immunity develops, but sequential pooled FECs can still provide an indication of pasture contamination as the season progresses.

There are also indirect indicators of which animals are likely to have a high worm burden and may need treatment. Animals failing to meet target live weight gain can be targeted for treatment, and regular weighing of animals can provide broader insights into productivity. Alongside this, general monitoring of thrive can give an early indication of parasite problems, which can then be investigated further.

Checking that wormers are working properly is the final, important step. A pooled FEC taken before and after a treatment (one week after treatment with a 2-LV product, and 2 weeks after a 1-BZ or 3-ML) with an egg count reduction of less than 95% may be a sign of resistance. But, it’s important to remember that treatments can be ineffective for other reasons, such as incorrect dosing or administration.

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