New Research from MSD Animal Health Reveals “Hidden” Parasitic Infections Cost Global Dairy Industry Billions Each Year

Contrasting data from the United States, Brazil and Europe highlight urgent need for region-specific, integrated parasite control

Rahway, NJ, June 4, 2026 –  MSD Animal Health, a division of Merck & Co., Inc., Rahway, N.J., USA (NYSE:MRK), today announced a comprehensive scientific review of dairy cattle parasites has revealed that “hidden” infections are costing the global cattle industry billions of dollars every year. The publication, which draws together data from the United States, Brazil, Europe and other key cattle-producing regions, outlines regional differences in parasite prevalence and the best methods for parasite control, highlighting that internal and external parasites remain among the costliest yet underrecognized threats to modern dairy production. Specifically, parasites cause illness and death, reduce milk production, slow weight gain, and harm carcass quality, with productivity losses far outweighing the direct cost of treatment.
 
Published in Parasites & Vectors, “The economic impact of endo- and ectoparasites in dairy cattle” shows that more than 80% of the total economic burden associated with dairy cattle parasites is linked to reduced performance. This underscores how even modest, ongoing reductions in milk yield can accumulate into major financial losses at the herd, regional and national levels. The full paper is available at https://rdcu.be/eSKWn.
 
“Parasites are a global problem hiding in plain sight. They are often invisible in day-to-day farm management, but their negative impact on milk yield, fertility and animal health is enormous,” said Robert P. Lavan MS, MPVM, DVM, DACVPM, study author. “Our analysis shows that smarter, integrated control strategies could unlock major productivity gains and help protect the long‑term effectiveness of existing treatments.”

Billions In Losses Worldwide, But Parasites that Drive Damage Vary from Region to Region

While overall economic damage is similar across regions, the main culprits driving the losses vary significantly by geography, climate and production system.
 
United States: Internal Worms Dominate Losses
 
In the United States, gastrointestinal (GI) nematodes are the primary parasite challenge. These internal worms quietly reduce milk production, slow the growth of replacement heifers and impair fertility. Across the national cattle herd, GI nematodes alone are estimated to cause more than US$3 billion in losses every year. Subclinical infections typically reduce milk yield by an estimated 0.3–1 liter per cow per day, meaning many farms are losing income without obvious clinical signs of disease. Findings from a 2025 market research survey conducted by MSD Animal Health further show that even modest, sustained production losses linked to internal parasites can accumulate into substantial herd-level and national economic impacts.
 
Brazil: Ticks and Tick-Borne Diseases Impose Significant Burden
 
Brazil, one of the world’s largest cattle producers, faces one of the largest parasite-related economic burdens in the global dairy sector. Here, GI nematodes are a leading challenge, but ticks and tickborne diseases also impose a significant economic burden, with annual impacts in the multibillion-dollar range. The single-host tick Rhipicephalus (Boophilus) microplus and the pathogens it transmits (Babesia, Anaplasma) drive substantial losses in milk yield, weight gain and animal survival. Year-round grazing in warm, humid conditions creates constant parasite pressure, and cattle are often exposed simultaneously to ticks, internal worms and liver fluke. Climate conditions and increasing resistance to antiparasitic treatments make effective control more challenging.
 
Europe And Other Temperate Regions: Worms and Liver Fluke at the Forefront
 
In Europe and other temperate regions, GI nematodes and liver fluke drive the most economic impact in dairy production. Across European ruminants, endoparasites are estimated to cost around US$2.07 billion annually, with dairy helminths accounting for roughly US$1.08 billion. Liver fluke (fasciolosis) alone affects more than 600 million animals worldwide, contributing an estimated US$2 billion to US$3 billion in losses each year, largely due to reduced productivity and liver condemnation at slaughter.

Climate and Production Systems Shape Parasite Risk

The review underlines how climate and production systems strongly influence parasite profiles and control options. For example, in the United States and Europe, many dairy herds are housed or managed in semi-intensive systems with defined grazing seasons. Cold winters naturally reduce parasite survival on pasture and create clear windows for strategic treatments and pasture rotation.

In Brazil and other tropical and subtropical regions, high temperatures and humidity allow parasites, especially ticks and GI nematodes, to thrive nearly year-round. This makes parasite management more complex, increasing treatment frequency and costs. Supporting market research findings from MSD Animal Health also suggest that these factors can accelerate resistance development when parasite control relies heavily on frequent, non‑targeted treatments.

“The same parasite control playbook cannot simply be copied from one region to another,” said Tiago Arantes, Associate Vice President, Ruminants Business Lead, MSD Animal Health. “Effective strategies must match the local climate, production system and dominant parasitic threats.”

Integrated, evidence-based control is key
The review calls for a shift away from routine, calendar-based deworming toward more integrated strategies that combine diagnostics, targeted treatments and improved management practices, reflecting growing concerns about resistance and declining durability of control. Key recommendations include:

• Targeted and selective interventions focused on high-risk periods, such as calving, turnout or key liver fluke seasons, and on the animals or groups most likely to benefit, rather than blanket treatment of entire herds at fixed times of the year.
• Expanded use of diagnostics to inform treatments and monitor effectiveness, including routine fecal egg counts (FEC), fecal egg count reduction tests (FECRT), and blood or milk-based assays.
• Improved pasture, housing and environmental management, including rotation, drainage, hygiene and integrated pest management for flies and ticks.
• Broader adoption of complementary control approaches, such as tick vaccines and genetic selection for more parasite-resistant cattle in regions with sustained parasite pressure.
• Increased producer education and awareness around subclinical parasitism, resistance risks and the economic value of diagnostics-driven decision-making.

Supporting market research reinforces this conclusion, showing that parasite-related losses are largely driven by hidden productivity impacts and variable parasite pressure. Producer and veterinarian insights further highlight that repeated, nonselective treatments often fail to deliver lasting benefits, while contributing to growing concerns around resistance, particularly in flies and intestinal worms.

“We already have many of the tools needed to significantly reduce parasite losses in dairy systems,” said Arantes. “The challenge is to apply them in a more strategic and region-specific way, and to invest in new solutions where resistance has eroded existing options.”