Ensure Effective Worm Control In Intensive Grazing

UK - Effective worm control is more essential than ever in high intensity grazing regimes designed to optimise grassland productivity and stock performance, according to a detailed review of the impact of grazing management on cattle and sheep parasites published this spring by EBLEX – the industry body for English beef and lamb levy payers.
calendar icon 11 April 2011
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The review, undertaken jointly for EBLEX and HCC by ADAS, confirms the extent to which intensive grazing exposes stock to high levels of gastro-intestinal parasite intake.

The majority of parasite larvae are typically found towards the base of the sward but will migrate upwards in favourable conditions. Grazing to the target sward height of 4-6 cm for sheep and 6-8 cm for cattle as recommended for the greatest productivity exposes stock to infectious larvae. Allowing swards to be get above target heights may not reduce the risk significantly, with evidence of larval density being evenly distributed throughout the grazing horizon of taller ryegrass swards, but will reduce feed quality.

Although longer rest periods in rotational grazing systems are recognised as lowering larval populations, the length of parasite life cycles means that rest periods of 3-7 weeks can coincide with peak levels of infective third-stage (L3) larvae, creating ideal conditions for parasite proliferation.

Larvae tend to travel only up to 30 cm from dung pats in the absence of heavy rain splashing.

Even so, the natural tendency of grazing livestock to reject herbage around them is unlikely to be of much value in limiting infection levels either. Indeed, rejections were found to be highest around very fresh faeces which actually pose less of a risk because L3 larvae have yet to develop. In contrast, grazing close to dung pats is commonly observed a month after deposition when levels of infective larvae may be at their highest. Rejections are known to be significantly lower overall at higher grazing intensities when grass supply may be limited.

As well as maintaining the best anthelmintic control programmes, the review – available from the research and development section of the EBLEX website (www.eblex.org.uk) from early May – makes several grassland management suggestions to tackle the particular intensive grazing parasite threat:

  • Grazing stock on pastures not used by the same species the previous year is the best way of reducing initial infectivity levels;
  • Alternating or mixing cattle and sheep grazing within the season can reduce infection levels in both species as well as improving their performance;
  • Back-fencing grazed areas of fields occupied for more than four days will limit stock exposure to early emerging larvae from dung pats as well as protecting regrowths;
  • Employing alternative forages with anti-parasitic activity like chicory, lucerne or red or white clover may combat parasite infections as well as producing pasture conditions less amenable to larval survival and movement.

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