Principal Partner


A formula for success

Although cows are generally resilient to clinical disease caused by gutworm Ostertagia ostertagi, the hidden, subclinical effects on dairy performance can be significant. An effective worming strategy using EPRINEX® Pour-on can mitigate such losses in productivity and maintain performance throughout the animal’s productive life.


EPRINEX® can be trusted to remove damaging gutworms from dairy herds because:

  • It is manufactured by Merial, tried and trusted parasite experts
  • It has been relied on by farmers since 1997 – no other eprinomectin product has such heritage
  • It has been proven in over 12 research studies, over 14 years, involving more than 8,000 cows across the world


EPRINEX® has been proven to have a long-lasting effect against worm species, including Ostertagia ostertagi and Dictyocaulus viviparus.

Effective for:

14 days against

  • Nematodirus helvetianus
  • Haemonchus placei.

21 days against

  • Cooperia oncophora
  • Cooperia punctata
  • Cooperia surnabada
  • Trichostrongylus axei
  • Trichostrongylus colubriformis

28 days against

  • Ostertagia ostertagi
  • Ostertagia lyrata
  • Dictyocaulus viviparus
  • Oesophagostomum radiatum

EPRINEX® has been delivering results for thousands of farmers for 20 years. Over 13,600,000 cows have been treated with EPRINEX® in the UK & ROI since *2000 with Zero milk withhold.


Discarding milk is not an issue with EPRINEX®. Individual cows can be treated at any stage of production, including calving and lactation. The whole herd can be treated at grass or at housing to protect against worms and control external parasites.


Studies to investigate the impact of adverse climatic conditions on the performance of EPRINEX® have shown that it remains highly effective against worm species including Ostertagia ostertagi, Cooperia oncophora and

Dictyocaulus viviparus even when cattle are exposed to heavy rain before or after treatment.16


EPRINEX® is licensed to control 15 species of gastrointestinal roundworm, including the immature, adult and inhibited stages of the major worm species Ostergia ostertagi,Cooperia spp and the cattle lungworm Dictyocaulus viviparus. It also controls external parasites chorioptic and sarcoptic mange mites, and biting and sucking lice.


In a comparative study, faecal egg output decreased the fastest in cattle treated with EPRINEX®. Significant reductions were seen as soon as the second day after treatment, and by day three, 88% of cattle were no longer shedding worm eggs.17


EPRINEX® is the only Pour-on proven in over 12 research studies, over 14 years, involving more than 8,000 cows across the world.

EPRINEX® has been proven to increase the milk yield in cows with gutworms by up to 2.6 additional litres of milk per cow, per day.4  

Trusted by farmers since its launch in 1997, millions of cows* around the world have been treated with it to control 15 species of worms and external parasites.

Our volume of evidence:


The cost of a gutworm burden on adult dairy cows is well documented. An increasing volume of evidence demonstrates that by removing gutworms with EPRINEX®, milk yield can be increased. In fact, worming adult dairy cows it has been shown to increase milk yield by as much as 2.6 litres per cow per day.4

Dealing with parasites to ensure optimum productivity starts with youngstock. Dairy heifers in their first grazing season are naïve to parasites. Effective parasite control at this critical time is key to rearing healthy, productive heifers.

The parasite facts

  • Left uncontrolled, parasite burdens will prevent dairy heifers from sustaining the growth rates of 0.7-0.8 kg/day required to achieve calving at 24 months
  • A reduction in liveweight due to poor parasite control during the first grazing season will not be compensated for during the second season at grass, affected animals will remain lighter10
  • Earlier onset of puberty and increased mammary development have been observed in strategically wormed heifers in comparison to those left untreated11, 12
  • Appropriate parasite control in growing youngstock can help them reach target weights at the optimum age, and so increase their production potential
  • Effective parasite control can reduce the costs associated with rearing replacement heifers


Merial Animal Health supports and promotes the MOO Test. Data from six years of UK tests, between 2009 and 2014, reveals that many dairy herds are hampered by a high gutworm challenge.


Calving is a key period in the production cycle. Careful cow and heifer management during this period is critical to the animal’s health and productivity throughout the subsequent lactation.

Studies have shown that worming dairy cows and heifers with EPRINEX® has resulted in improved fertility:

  • Cows treated with EPRINEX® at calving have been shown to have improved calving to conception intervals13, 14, reducing time to get them back into calf
  • Treating heifers is also beneficial, with higher conception rates at first service13 compared to untreated cattle

After calving, improved appetite and higher intake of dry matter helps cows to bridge the energy gap, which leads to maximised production. Cows treated for gutworm with EPRINEX® have been shown to increase their grazing time by almost an hour, compared to untreated cows.15


Convenient because:

  • It can be used to treat at grass or at housing and there is zero milk withhold
  • It is available in large backpack style bottles that are easy to use when treating large herds
  • It comes in a range of pack sizes from 250ml to 5L
  • The Breeze Applicator has been specially designed for EPRINEX® to ensure easy and accurate application

Infective larvae of the gutworm Ostertagia ostertagi are ingested by cows at pasture. They enter the abomasum, where they burrow into the stomach wall. Then, depending on the time of year, they either develop into adult worms within three weeks, or halt their development over the winter period. In this case, they remain encysted in the stomach wall, ready to emerge in early spring as adult worms.

Adult worms lay eggs, which are excreted in the faeces. The eggs hatch within the dung pat into young larvae (first, second and third stage larvae). The third infective stage larvae migrate onto the pasture, where they are ingested by grazing cattle, to complete the cycle.



* Taking into account the volume sold, over 13.6 million cows have been treated with EPRINEX® in the UK and Ireland since 2000, based on treating cows weighing 600kg.

  1. Charlier et al., Veterinary Parasitology 143 (2007) 322-328
  2. Reist et al., Veterinary Record 151 (2002) 377-380
  3. Nodtvelt et al., Veterinary Parasitology 105 (2002) 191-206
  4. Reist et al., Veterinary Record 168 (2011) 484-487
  5. McPherson et al., New Zealand Veterinary Journal 49 (2001) 106-110
  6. Little et al., Proceedings of the 22nd World Buiatrics Congress, Hannover, 2002
  7. Schoett et al., Proceedings of the 22nd World Buiatrics Congress, Hannover, 2002
  8. Watson & Forbes, UK Vet 5 (2000) 48-50
  9. Verschave et al. BMC Veterinary Research 10 (2014) 264
  10. Larsson et al., Veterinary Parasitology 175 (2011) 134-140
  11. Mejía et al., Veterinary Record 165 (2009) 143–146
  12. Perria et al., Veterinary Parasitol 198 (2013) 345-350
  13. Sanchez et al., Preventative Veterinary Medicine (2002) 56:165-177
  14. McPherson et al., Proceedings of the American Association of Veterinary Parasitologists. 44th Annual Meeting 1999, New Orleans, Louisiana, USA, Abstr. 28.
  15. Forbes et al., 19th WAAVP Congress 2003, New Orleans.
  16. Gogolewski et al., Veterinary Parasitology 69 (1997) 95-102
  17. Paul A. et al., Proceedings of the American Association of Veterinary Parasitologists. 45th Annual Meeting, Salt lake City, USA, 2000


Use medicines responsibly. www.noah.co.uk/responsible

EPRINEX® Pour-on for Beef and Dairy Cattle contains eprinomectin. EPRINEX® and the steerhead® logo are registered trademarks of Merial Ltd. ©Merial 2017. All rights reserved. Legal category POM VPS (UK), LM (Ireland). Advice on the use of this or alternative medicines must be sought from the medicine prescriber. Read packaging before use. For further information refer to the datasheet, contact Merial Animal Health Ltd, CM19 5TG, UK, or call the Merial Customer Support Centre on 0800 592 699 (UK), 1850 783 783 (Ireland).

Merial is now part of Boehringer Ingelheim.