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Managing parasites for productivity during housing

Merial-Sanofi_Logo_rgbHousing provides an ideal opportunity to address a variety of parasites that may have been picked up over the grazing season. The four common parasite groups that need consideration are gut worms, lungworms, liver fluke and external parasites (lice and mange).  As animals will not pick up any new infections whilst housed, this strategic treatment will help to achieve all three of the main objectives of a parasite management plan:

  1. Prevent clinical disease
  2. Improve productivity
  3. Reduce pasture contamination

It is particularly important at this time of year to take into account parasite prevalence, disease risk and spectrum of activity when selecting products in order to maximise the benefits gained. Whilst it is widely recognised that young animals are generally more susceptible to parasite related disease, it is now acknowledged that parasites can have an impact on the productivity of cattle of all ages. An assessment of the performance parameters that can be affected by parasites, such as: growth rate; fertility; milk yield and composition; and body condition, in combination with blood, bulk milk or faecal testing, will provide a valuable insight into the effectiveness of the parasite control measures over the grazing season1.

One of the key disease threats to consider at housing is Type II ostertagiasis caused by the mass emergence of inhibited larvae in the Spring. Using a wormer that is effective against both adult and inhibited larvae of Ostertagia ostertagi will reduce this risk. The macrocyclic lactones (e.g. ivermectin, eprinomectin etc) are the ideal choice for a housing treatment as they will not only address this problem but will also treat lungworm and, depending on the molecule and route of delivery, ectoparasites. They are also often formulated in combination with a flukicide. Johnson2 showed that housed cattle on intensive rations that were treated with ivermectin achieved a 5.2% improvement in average daily weight gain compared to controls. This was significantly increased by a further 3% in those animals treated with a combination of ivermectin and clorsulon (IVOMEC® Super).

The questions of which flukicide to use and when to treat can be challenging and confusing, complicated further still by the restricted range of products available for dairy cattle. Convenience should not be the only factor in product choice and it may be preferable to use a separate wormer and flukicide product.

Table 1 outlines the various active ingredients and formulations available and their spectrum of activity.

Age of fluke table

Table 1: Summary of spectrum of activity of commonly available flukicides (coloured area based on >80% efficacy)3.

Cattle and sheep are infected by the same species of liver fluke (Fasciola hepatica), although typically only sheep are affected by acute fasciolosis, which can result in the sudden death of up to 10% of previously healthy animals4. Triclabendazole is currently the only treatment available for this costly disease and it is also the one flukicide with reports of anthelmintic resistance. It is, therefore, essential to conserve this molecule for when it is genuinely needed to try to slow down the development of resistance.

Recent evidence suggests that the inclusion of early immature liver fluke in the housing treatment for cattle is not as critical as was previously thought. One study (see Chart 1) examined condemned cattle livers in abattoirs in the Autumn months and found that 97% of the fluke present were late immature or adults with only 3% present as early immature fluke5.

Chart 1

Chart 1: Stages of fluke present in condemned cattle livers in abattoirs in the Autumn months, expressed as a percentage of total fluke found.

In another study6, beef cattle were housed and treated with either an ivermectin/clorsulon combination (Ivomec® Super), or ivermectin (Ivomec® Classic Injection) plus nitroxynil (Trodax®) or Triclabendazole  (Fasinex® Cattle oral drench), or ivermectin (Ivomec® Classic Injection) only (no flukicide). There were no significant differences in liveweight gain between the different flukicide groups, as shown in Chart 2, and no cattle developed clinical signs of fluke infection during the study. The study did find that flukicide treatment of animals that had positive fluke egg counts at housing resulted in significantly higher weight gain over the 112-day trial period than cattle that were not treated.

Chart 2

Chart 2: Liveweight gain (kg) in cattle with positive fluke egg counts at housing treated with different flukicide groups.

It is also worth noting that cattle that were negative for fluke eggs at housing grew on average 20.5kg more than those that were positive, irrespective of treatment, so it is important to remember the third objective of parasite control - reduce pasture contamination, and view the housing dose as a way of reducing parasite challenge in the following season.

Treating at the point of housing will ensure that animals benefit immediately from the production improvements associated with fluke control. In order to ensure that this is sustained for the entire housing period and animals are turned out fluke-free in the Spring, cattle should either be tested and retreated if necessary or retreated strategically during housing. The required interval will depend on the product used but the same principle would apply to all of the available flukicides.

References:

1. Animal Health Ireland, Parasite Control Leaflet Series Vol.1. Ver. 2. October 2013 (http://www.animalhealthireland.ie/page.php?id=37)

2. Johnson EG, Agri-practice 1991; 12:33-35.

3. Adapted from Fairweather and Boray, The Veterinary Journal 1999, 158, 81-112

4. NADIS, Liver Fluke Control in Sheep, Health Bulletin 2015. (/bulletins/liver-fluke-control-in-sheep.aspx)

5. MacGillivray F et al, Intern J Appl Res Vet Med 2013. 11(1): 1-6

6. Forbes AB et al, Veterinary Record 2015. 176(13):333

Ivomec classic Ivomec super Trodax

Merial-Sanofi_Logo_rgb Ivomec® Classic injection or pour-on for cattle contains ivermectin. Ivomec® Super injection for cattle contains ivermectin and clorsulon. Trodax® 34% w/v solution for injection contains nitroxynil. Ivomec® and Trodax® are registered trademarks of Merial Ltd. ©Merial Ltd 2016. All rights reserved. Legal category: POM-VPS (UK), LM (Ireland). Advice on the use of these or alternative medicines must be sought from the medicine prescriber. For further information refer to the datasheet, contact Merial Customer Support Centre on 0800 592699 (UK), 1850 783 783 (Ireland).

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