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Flock, Stock &

Smoking Farrow Issue 9

www.markethallvets.co.uk

Article by Rebecca Cole

Worming Sheep and Managing Resistance — PART 1

Worm control in sheep flocks is a traditional part of health and production management, which is traditionally dependent on the use of effective anthelmintics. Unfortunately there is a growing concern over the development of resistance to common anthelmintics. If we continue to not address the problem of resistance this could prove one of the biggest challenges to the UK sheep industry. We need to find a balance between worm control using chemicals and practical management techniques. For this we need to understand which parasites are present on farm, if there is any resistance to anthelmintic groups and how we can implement management options to reduce worm burdens in sheep.

Traditionally it was advised for farmers to rotate be-tween different classes of anthelmintics every 1-2yrs. This strategy was intended to prolong the longevity of each group, to allow a break in the use of different clas-ses. However, now we have widespread resistance, this strategy is less effective. It is better to target parasites with narrow spectrum products and effective quarantine. We need to use the right product at the right time with individual farm plans and advice.

Currently in the UK there is widespread resistance to the 1-BZ (Benzimidazole), high levels of resistance to 2-LV (Levamisole) and growing resistance to 3-ML (Macrocyclic lactones).

It was also commonly advised to ‘dose’ and ‘move’ to clean pastures. This is now thought to select for anthel-mintic resistance. To avoid selection for anthelmintic resistance it is better to adopt different practices: Targeted selective treatments – Leave 10% of the flock untreated, then move to low-contaminated pastures. Will require use of a highly efficacious treatment to ensure rest of the flock are covered. An EU funded PARASOL project is looking into determining more accurately which animals should be targeted for treatment. Obvious ones are sick ewes, ewes with poor body condition score. Delay the ‘move’ after ‘dose’ – Allow sheep to become lightly re-infected before moving to low contaminated pastures, roughly 4-7days may be sufficient. Imported sheep are a big contribution to spread of anthelmintic resistance between farms. To prevent intro-duction of resistant worms effective quarantine treatments are essential.

Anthelmintic resistant worms = Heritable ability of a parasite to tolerate treatment with an effective dose of anthelmintic.

‘in-refugia’ = A sub-population of worms that are on the pasture (ie: not in the sheep) at the time of worming and therefore are not exposed to the wormer at the time of treatment. This population is much larger than the population present in the sheep.

Nematodirus battus: Now seen across the year rather than just spring. Requires a period of cold weather, followed by a increase in temperature (>10oc) for eggs to hatch larvae. This usually occurs in the UK between April-June, leading to high levels of infec-tivity from June-Septmeber, when young lambs are grazing at pasture. High levels of rainfall lead to increased infectivity of larvae later in season. L3 can over-winter on pasture leading to a source of infection to grazing sheep early in spring. L3 ingestion causes damage to the small intestine – causes onset of Diarrhoea, dehydration, inappetance and thirst. Usually seen as gastroenteritis in lambs at spring and autumn. Treat Nematodirus in lambs with a 1-BZ or 2-LV gp.

Practice News

Sadly we said goodbye

to Stephen this month,

he will be greatly

missed at the practice

and we thank him for

all his hard work.

We would like to

welcome Rita

Serrenho to the

practice. Rita is from

Portugal and qualified

from University of

Lisbon in 2015. Rita

was a founding

member and president

of the Students´

Bovine Group. She has

completed a Master’s

in Economics of

Mastitis and Milk

quality in Portugal. In

2016 underwent a

training program in

the USA. Before

joining Market Halls

Vets she saw practice

in Portugal, Scotland

and Ireland.

We hope she enjoys

working and living in

west Wales.

Article by

Rebecca Cole

BVSc MRCVS

Haemonchus contortus (‘Barbers pole worm’): Favours warm and wet conditions. Pastures can become highly infected between mid-spring to late autumn. Doesn’t over-winter well, so hypobiosis in sheep is an im-portant means for it to survive over-winter in the UK. Clinical signs associated with blood loss, regenerative anae-mia. Acute – weakness, collapse and sudden death Sub-acute – bottle jaw Chronic – weight loss, poor body condition, bottle jaw, weak-ness and lethargy. NOT diarrhoea. Closantel is a good option for ewes and lambs on ‘at risk’ farms .

Lungworm: There are several species of lungworm affecting sheep. Usually a less severe disease than in cattle. Can cause coughing and dysp-noea in autumn grazed animals.

Product

Spectrum of activity

Activity against Roundworms

and Lungworm

Activity

against fluke

Notes

Gp 1-BZs (White)

Albendazole Broad

Yes

>10wks Requires 50% higher dose for fluke Fenbendazole Broad Menbendazole Broad Various activity against N.battus Ricobendazole Broad >10wks Requires 50% higher dose for fluke Oxfendazole Broad Triclabendazole Narrow >2ds

Gp 2-LV (Yellow)

Levimasole Broad Yes Injectable and oral formulations

Gp 3-ML (Clear)

Ivermectin Broad

Yes

Endectocidal activity. Injectable and oral forms

Moxidectin Broad Endectocidal activity. Persistent activity against some nematodes. Injectable and oral forms

Dormamectin Broad Endectocidal activity. Injectable only Gp 4-AD (Orange)

Monepantel Broad Yes

Gp 5-SI (Purple)

Derquantel Broad

Yes

Only as a dual active product in conjunc-tion with Abamectin a 3-ML

Substituted phenols and

salicylanilides

Closantel Narrow

Yes

>6wks Persistent activity against H. contortus

Nitroxynil >6wks Injectable only Oxyclozanide >10wks

Table of worming products and activity:

FEC monitoring: Can be used to :

Help determine need to treat

Test the efficacy of a treatment

Give information on the amount of contamination on pastures

FECs can help strategically treat with anthelmintics during periods of risk. FECs don’t always strongly relate to the size of the worm burden and different parasites have different pathogenicities. FECs will tell you of the worms picked up 3+ weeks earlier.

Tapeworm (Taenia multiceps and Coneurus cerebralis (GID) are some examples): Hydatid cysts found in lung and liver, usually asymptomatic but a public health concern and a big reason for organ and carcass condemnation at slaughter, a big economic loss. Dogs and foxes act as the final host of tapewroms and integral to the lifecycle. Control of worms in these animals, not allowing access to sheep carcasses or ability to defecate on feed is vital for control of tapeworm in sheep.

Teladorsagia spp. (Ostertagia): Tends to be seen from mid-summer onwards in lambs that ingest large numbers of larvae during their first season of grazing. Some abomasal nematodes are able to arrest their development as larvae and stay in a period of dormancy called hypobiosis. Typically occurs in larvae ingested in late autumn and winter, delaying egg production until the following spring. Causes inappetance, diarrhoea, dehydration, weight loss and death. Synchronous resumption of hypobosed larvae can lead to disease in yearling animals early spring.

Trichostrongylus spp. (‘black scour worm’): Usually seen in store/replacement lambs in autumn and winter. Can occur in lambs from late summer with high infection pressures. See reduced growth rates, reduced BCS, diarrhoea and death.