Unexpected Decrease in Milk Production after Fenbendazole Treatment of Dairy Cows during Early Grazing Season

Area of Science:

• Veterinary Medicine
• Parasitology
• Animal Science

Background:

• Gastrointestinal nematode (GIN) infections negatively impact dairy cow milk production (MP).
• Spring targeted-selective anthelmintic treatment is a strategy to potentially optimize MP in grazing cows.
• The efficacy and impact of such treatments on MP require further investigation.

Purpose of the Study:

• To evaluate the effect of spring anthelmintic treatment on MP in grazing dairy cows.
• To identify herd and individual indicators associated with the post-treatment MP response.

Main Methods:

• A randomized controlled clinical trial involving 578 cows across 13 dairy farms in western France.
• Treatment group received fenbendazole orally, while the control group remained untreated.
• MP, serum pepsinogen, anti-Ostertagia antibody levels (ODR), and fecal egg counts were measured.

Main Results:

• Spring anthelmintic treatment resulted in a significant detrimental effect on MP (-0.92 kg/cow/day).
• Negative MP response was more pronounced in high-producing cows, those untreated during housing, and cows with high pepsinogen levels.
• Herds with high Time of Effective Contact (TEC) or high bulk tank milk (BTM) Ostertagia ODR also showed a greater negative response.

Conclusions:

• Unexpectedly, spring anthelmintic treatment negatively impacted milk production in dairy cows.
• The decrease in MP may be linked to immuno-inflammatory mechanisms.
• Non-persistent anthelmintic treatment in immunized adult dairy cows is not recommended in the early grazing season pending further research.