The Economic Impact of Parasite Control on Profitable Heifer Production

Infection by parasites, even in the absence of clinical disease, is one of the most common reasons for reduced productivity and economic losses in the cattle farming business. Depending on the level of infection it can lead to a reduction in feed intake and weight gain, and impact on milk production and fertility. Treatment can therefore make a significant difference to productivity levels. For example, studies show that the milk-yield response to anthelmintic treatment in pastured dairy herds was observed to be around 1kg per cow per day1. The average differences in weight gain between treated first-season grazing calves and untreated control calves with subclinical or clinical infections were estimated at 150g per day and 315g per day2.

While the impact of parasite infection on cattle is now commonly accepted, the wider economic impact is not always known. Sustainable control strategies are increasingly important for the growth of healthy heifers to ensure they grow quickly to their full genetic potential. Diagnosing parasite infections and monitoring heifer performance is therefore very important.

The benefits of producing heifers that calve at 24 months are significant, and include reduced cost of producing replacements, lower culling rates, and increased lifetime profitability through additional lactation periods.

In order to achieve a 24 month average age at calving heifers must reach approximately 60% of mature weight by 14 months of age. This requires an average daily weight gain of at least 0.7-0.8 kg during the period between weaning and bulling.

This focus on growth must be maintained during pregnancy since a continued steady weight gain is required if heifers are to calve at 90% of mature weight, and transition well into lactation. However, it’s more important that growing cattle meet breed-appropriate target weights since the onset of puberty and first oestrus is more closely linked to heifer weight, body size and condition score than age.

Heifers have high nutrient requirements as they grow and get ready for calving. A heavy parasite burden will draw on these resources, reducing the nutrients available for growth and slowing the time they take to reach their mature weight and become ready to conceive. This will reduce the animal’s productive life and mean potential economic losses which can be worrying and costly.

The impact of parasite challenge as heifers approach reproductive age is supported by studies showing increased mammary development and earlier onset of puberty in strategically wormed heifers in comparison to those left untreated3,4.

Effective parasite control plays a central role in managing heifer health; protecting her future fertility, helping her get back into calf more quickly after the first calving. Efficient heifer production therefore relies on setting and meeting targets for productivity.

Before considering the parasites themselves it is worth considering the performance of the stock over the previous grazing season and how it compared with expectations or targets. Growth rates of young stock in their first and second grazing season are useful indicators of effective parasite control. Losses in liveweight gain due to poor parasite control during a heifer’s first grazing season will not be recouped during the second year at grass5. Affected animals will not catch up, and this will impact on their ability to meet important growth milestones, which could result in an increased age at first calving.

To manage this challenge it is important to set growth targets for young stock at grass, and monitor their performance through regular weighing to ensure these are being met. Alongside this, it’s critical to manage and feed accordingly and use anthelmintics, integrated with a grazing management system, to ensure the potential impact of parasites is controlled.

Effective parasite control is proven to make significant improvements to weight gain over a grazing season, whilst also contributing to reduced pasture contamination6,7,8. Undertaking a parasite risk assessment before treatment takes place will allow a more targeted approach to be implemented, and will increase the sustainability of anthelmintic control, and reduce selection for resistance. Farmers and vets should work together to develop a plan that sets targets and uses a risk assessment based approach to determining whether gutworm treatments are required.

It is important to understand the dynamics of the pasture larval threat and take measures to manage this. Reducing exposure to pasture challenge through altered grazing practices, specifically delayed turnout may result in higher technical efficiency and milk production9. Grazing management interventions do, however, need to be evaluated at the farm level so that they are appropriate.

Putting monitoring systems in place will help to determine when treatments are required, helping to avoid unnecessary treatments and minimising selection for resistant worms.

Regular assessment of treatment efficacy is also an important component of sustainable parasite control. A faecal egg count is performed on individual animals before treatment, and a follow up sample is obtained 14 days later where a 3-ML has been used, or seven days later where a 1-BZ or 2-LV product has been used. The counts are then compared. A reduction of greater than 95% will be seen when a product has been fully effective; where the response is lower than this further investigation should take place.

To slow the likelihood of wormer resistance on farm, all parasite control products should be used in accordance with the datasheet and product packaging.

Accurate dosing can only be achieved if you have accurate weights on every animal. Do not compromise on dosing equipment or scales to determine live weights. In order to ensure you get the best from your parasite control product:

  • Consult the label and/or datasheet before using a product
  • Maintain all equipment and cattle handling facilities
  • Choose the most appropriate product for the parasites present
  • Administer products at the right dose 
  • Store and handle products safely and correctly

Targeting the right animals with the right anthelmintic at the right time will maximise the efficacy of treatments, resulting in a more sustainable and profitable livestock business.


  1. Charlier, J., et al., (2019) Gastrointestinal nematode infections in adult dairy cattle: Impact on production, diagnosis and control. Veterinary Parasitology, 164(1): p. 70-79.
  2. Shaw, D.J., et al. (1998) Gastrointestinal nematode infections of firstgrazing season calves in Western Europe: general patterns and the effect of chemoprophylaxis. Veterinary Parasitology, 75(2): p. 115-131.
  3. Mejía et al (2009) Effect of anthelmintics on reproductive performance and first lactation culling rate in Holstein heifers. Veterinary Record 165: 143–146
  4. Perria et al (2013) Gastrointestinal parasite control during prepuberty improves mammary parenchyma development in Holstein heifers. Veterinary Parasitology, 198:345-350
  5. Larsson et al. (2011) Performance of second-season grazing cattle following different levels of parasite control in their first grazing season. Veterinary Parasitology 175 (2011) 134-140
  6. Walker, R.S., et al. (2013) Gastrointestinal nematode infection and performance of weaned stocker calves in response to anthelmintic control strategies. Veterinary Parasitology, 197(1): p. 152-159.
  7. Geurden, T., et al. (2004) Evaluation of the chemoprophylactic efficacy of 10% long acting injectable moxidectin against gastrointestinal nematode infections in calves in Belgium. Veterinary Parasitology, 120(4): p. 331-338.
  8. Baltzell, P., T. et al. (2015) A critical review and meta-analysis of the magnitude of the effect of anthelmintic use on stocker calf production parameters in Northern US States. Veterinary Parasitology, 2015. 214(1): p. 2-11.
  9. van der Voort, M., et al., (2017) Economic modelling of grazing management against gastrointestinal nematodes in dairy cattle. Veterinary Parasitology, 2017. 236: p. 68-75.

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1st April 2022

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