Controlling worms in cattle

Gastrointestinal parasites occur in all cattle farming areas of New Zealand. 

The primary species of concern are the Small brown stomach worm: Ostertagia ostertagi*; the Stomach hair worm: Trichostrongylus axei*; and the Small intestinal worm: Cooperia oncophora*, Cooperia pectinata*, Cooperia punctata*, Cooperia mcmasteri*; 

Economic impact 

Nutrition and effective roundworm parasite control are essential for successful beef and dairy farming in New Zealand.  A beef herd can be 15% more profitable if heifers are mated as yearlings. Additionally heifers must be grown to 300 kg to ensure they have attained puberty and will be cycling and are grown out enough to calve and re-breed successfully (1)

Dairy heifers reaching target liveweights will produce 8.5 kgMS more in their first lactation than if they are 10% below target (2)

The importance of fully effective anthelmintics in young cattle systems was illustrated in a 2012 system. In brief R1 Friesian bulls treated with a fully effective anthelmintic had a daily weight gain of 100 g greater than those treated with a less than fully effective anthelmintic, resulting in 6 kg difference after 60 days (3)  

Life cycle 

Worm species pass through three stages (4)

Host stage: Consumed infective L3 larvae mature into adults and reproduce. Egg laying commences about 18 days after ingestion. Mature worms can live within the gut for many months. The cattle immune system can expel worms or suppress egg laying.  

Dung stage: Dung containing worm eggs is passed from the beast to the pasture. Eggs develop through the L1, L2 and L3 stages. This process takes between 4 and 10 days, depending on temperature. L1 and L2 larvae feed on bacteria in the dung.  

Pasture stage: Infective L3 larvae wriggle out of the dung onto the ground and pasture. where they are consumed by cattle during grazing. Infective L3 larvae are reasonably tolerant of temperature. L3 larvae do not feed and uneaten larvae typically die three to six months after hatching once their energy reserves are used up. 

Controlling worms 

Most cattle farmers implement some form of worm control using anthelmintics (e.g. ‘drenches’) in combination with grazing management.  

  • strategic timing of treatments (e.g.  quarantine) 
  • the use of combination drenches wherever possible  
  • monitoring drench efficacy using worm egg counts (pre- and post-drench) 
  • monitoring drench resistance using faecal egg count reduction tests (FECRT), including larval differentiation. 

Quarantine drench  

Knowing the drench resistance status of your property by conducting a FECRT and then actively managing parasites to maintain or improve resistance status is essential. 

The importation of resistant parasites in bought in stock is recognized as posing one of the greatest risks to roundworm management. 

Drench resistant parasites are an increasing problem on New Zealand cattle farms. 

A 2007 (5) survey of 62 randomly selected farms (5) found: 

  • Ivermectin resistance present on 92% of farms (Cooperia) 
  • BZ resistance on 76% of farms (Cooperia and Ostertagia) 
  • Levamisole resistance on 6% of farms (Ostertagia) 
  • On 75% of farms Cooperia resistant to both ivermectin and albendazole 
  • Ostertagia resistant to ivermectin found on 6% of farms, to albendazole on 24% 
  • It is widely acknowledged that dairy farms esp. heifer grazing blocks will be in similar or worse situation.(6) 

Zolvix Plus is the only novel anthelmintic registered for use in cattle and therefore must be considered an essential part of cattle quarantine procedures. 

It is important to understand that effective quarantining of bought in stock is not simply about which drench is used. Consideration must be given to holding treated animals in the yards for 24 hours after dosing, and then releasing them onto contaminated or “dirty” pasture to dilute the eggs of any resistant parasites which may have survived the quarantine treatment (4).  

Which drench to choose? 

A wide range of oral, injectable and pour on drenches are available to control gastrointestinal parasites. These drenches can contain one, two, three or even four active ingredients from the following classes of broad-spectrum drenches:  

  • Benzimidazoles (BZ or white drenches), which were introduced to the N.Z. market in the 1960s. Examples include thibendazole, parbendazole, oxbendazole, mebendazole fenbendazole and albendazole.  
  • Levamisoles (LEVs or clear drenches), which were introduced to the N.Z. market in 1968. Examples include levamisole and morantel.  
  • Macrocyclic lactones (MLs or mectins), which were introduced to the N.Z. market in the late 1980s. Examples include abamectin, eprinomectin, ivermectin and moxidectin. 
  • Amino-Acetonitrile Derivatives (AADs or ‘orange’ drenches), which were introduced to the N.Z. market in 2009, and registered for use in cattle in 2019. Monepantel, one of the active ingredients in Zolvix Plus, is the only active ingredient in this class. 


Zolvix™ Plus/Zolvix 

Zolvix Plus (25 g/L monepantel and 2 g/L abamectin) from Elanco is ideal for use in strategic cattle drenching programs wherever certainty in roundworm control is required such as quarantine treatments or as a knock out treatment.  

Zolvix Plus is the only combination drench that contains 25 g/L monepantel. Monepantel’s unique mode of action provides efficacy against a broad spectrum of internal parasites of cattle, including single, double and triple resistant strains.  

Zolvix Plus is the first choice for cattle quarantine drenching. Always read and follow label directions. 


Trusted solutions and advice from Elanco   

Elanco is an industry leader in cattle worm solutions with the product Zolvix Plus coupled with benchmark technical support and customer service. For any information or technical advice on managing sheep roundworms, contact Elanco 0800446121 

Resistance may develop to any chemical. Ask your local veterinary practitioner or animal health advisor for recommended parasite management practices for your area to reduce development of resistance. It is advisable that a resistance test be conducted before any parasite treatment is used. Use in accordance with the registered label directions and regional drench decision guidelines ( 



2) “Heifer management: The impact of undergrown heifers” L McNaughton, T Brownlie, S McDougall. Proceedings of The Society of Dairy Cattle Veterinarians of the NZVA Annual Conference, 20147. 

3) “The effect of ML resistant Cooperia in healthy cattle”. Leigh, J. et al. (2013). Proceedings of the Society of Sheep and Beef Cattle Veterinarians of the NZVA, 

4) Wormwise Manual 2019 

5) “Being Wormwise for dairy.”  Chapman, V. (2016) Proceedings of the Society of Dairy Cattle Veterinarians of the NZVA Annual Conference (Jan). 

6) Waghorn, T.S. et al. (2006). Prevalence of anthelmintic resistance on sheep farms in New Zealand. NZVJ 54(Dec)(6): 271-277.