Bacillus thuringiensis var. Israelensis as a Larvacidal on a Rotational Grazing System for Ruminants to Combat Haemonchus contortus

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2017: $10,000.00
Projected End Date: 03/14/2018
Region: Southern
State: Tennessee
Principal Investigator:


  • Animals: goats, sheep


  • Animal Production: grazing - rotational, parasite control
  • Pest Management: biological control
  • Production Systems: organic agriculture


    • Haemonchus contortus continues to be a limiting factor on sheep production for small scale producers in the United States using a pasture based system. Hot and humid summer climate in the Southeastern US provide optimum conditions for H. contortus to develop from eggs deposited in feces to L2 and L3 larvae on warm and moist pastures. The current commercially available anthelmintics are becoming ineffective in many areas due to years of systematic deworming practices used by sheep and goat producers.

      New classes of anthelmintic are not being developed by pharmaceutical companies. Sustainable farming practices such as rotational grazing, use of FAMACHA scoring and administering copper oxide wire particles (COWP) as a bolus aids producers who wish to avoid using chemicals to treat animals destined for market or those wishing to use organic husbandry. However, even using a rotational grazing system, FAMACHA and COWP, producers continue to have losses from parasitic infections.

      Traditional internal worm strategies have focused on control through pharmaceutical anthelmintics.  More recent internal strategies include COWP and use of tannin rich forages to disrupt the parasite life cycle. External strategies to control H. contortus have been limited to dry lot feeding and rotational grazing. Additional external control strategies are needed to reduce the larvae that develop on pasture.

    Our project tested the theory that a naturally occurring bacteria, Bacillius thuringiensis (Bt), could be used as a larvacidal when applied to pasture/forage during a rotational rest period to find if it would be effective in reducing L3 larvae available for animal uptake. Biological agents such as Bt are considered to be organic control if they are one of the naturally occurring strains of bacterium.

    By spraying liquid Bt or spreading Bt granules on a pasture or paddock that recently had animals rotated off, our goal was to reduce larvae populations in the L2 and L3 stages making them unavailable for uptake by sheep once the animals are rotated back into the paddock during rotations.

    The project spanned 28 weeks during the Spring/Summer/Fall of 2017 and data is divided into three phases; a pre-test, Phase 1 and Phase 2.  During the pre-test phase (3-weeks) the lambs lived in a corral dry-lot and did not rotate while they were trained to stay within the electric fence that was used during Phase 1 and 2.  Phase 1 (18-weeks) consisted of 3 full rotations through a six paddock field that was sprayed with liquid Bt.  Phase 1 was not successful in showing a reduction in L3 available as evidenced by no difference between the control group and the treatment group.   Phase 2 (6-weeks) was a full rotation through the 6 paddock field that was sprayed with liquid Bt as before and additionally the treatment group was fed a small quantity of Bt daily during Phase 2.  During Phase 2 there was a statistically significant difference between the control group and the treatment group with a reduction in fecal egg counts (FEC) in the treatment group.

    Project objectives:

    For sheep farmer who desire to produce an organic carcass or those who wish to limit chemical inputs in their animals options are limited to COWP and tannin rich forages.

    Naturally occurring bacterium such as Bacillus thuringiensis (Bt) has been used by organic gardeners to control many species and sub-species of caterpillar and other insect larvae from damaging plants and crops. Bt works by encoding toxins that kill target species of insect larvae. The bacteria forms crystal protein toxins which when ingested by the larvae transform and attach in the gut of the larvae forming a pore. The larvae then fails to eat and starves thereby breaking the lifecycle.

    Bacillus thuringiensis variant Israelenis and variant Kurstaki have been tested as a larvacidal on sheep feces and found to be effective at reducing larval populations.

    By using a rotational grazing system, producers move animals from pastures where manure and potential Haemonchus contortus eggs have been deposited when grazing heights fall below set limits to maximize forage use and reduce the risk of worm infection. However, pastures can still remain infected by parasites waiting to complete the lifecycle when animals are rotated back onto pastures. Rotational grazing seeks to move animals before forage is grazed down near the ground where L3 larvae can survive in warm moist conditions.

    By spraying liquid Bt or spreading Bt granules on a pasture or paddock that has recently had animals rotated off, we seek to reduce larvae populations in the L2 and L3 stages making them unavailable for uptake by sheep once the animals are rotated back onto the paddock during rotations.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.