Parasitic diseases are among the leading causes of silent production losses in cattle systems. Internal parasites such as gastrointestinal nematodes, liver flukes, and lungworms, together with external parasites including ticks, flies, lice, and mange mites, reduce milk yield, feedlot performance, reproductive efficiency, and hide quality. Even subclinical parasitism may lower ADG by 5-15% and milk production by 5-10% without dramatic clinical signs. This article reviews the major internal and external parasites of cattle, diagnostic methods, strategic treatment programs, anthelmintic resistance management, and integrated parasite-control strategies.
Economic Impact
Parasitic diseases cause more than $3 billion in losses to global cattle production every year. In feedlot cattle, gastrointestinal nematodes may reduce ADG by 8-15% and worsen FCR by 5-10%. Liver fluke infection caused by Fasciola hepatica leads to condemnation of 100% of affected livers at slaughter and may reduce carcass weight by 5-10%. A well-designed strategic treatment program can prevent 70-80% of these losses (Charlier et al., 2014).
1. Internal Parasites (Endoparasites)
1.1 Gastrointestinal Nematodes
| Parasite | Location | Clinical Effect | Diagnosis |
|---|---|---|---|
| Ostertagia ostertagi | Abomasum | Diarrhea, reduced appetite, protein loss, and type I summer or type II winter ostertagiosis | Fecal egg count (FEC), serum or plasma pepsinogen |
| Cooperia spp. | Small intestine | Diarrhea, poor growth, with higher pathogenic importance in young stock | FEC |
| Haemonchus placei | Abomasum | Blood-sucking parasite causing anemia, edema, and in severe cases death | FEC, while FAMACHA is used more commonly in sheep and goats |
| Nematodirus spp. | Small intestine | Acute diarrhea and sudden death in calves | FEC because the eggs are characteristically large |
| Dictyocaulus viviparus | Lungs | Coughing, respiratory distress, and verminous pneumonia | Baermann technique for larval detection |
1.2 Liver Fluke (Fasciola hepatica)
Fasciolosis: Common in Turkey
- Life cycle: Egg → miracidium → snail host (Lymnaea) → cercaria → metacercaria on herbage → oral intake → migration to the liver
- Acute form: Migration of immature flukes through liver parenchyma causing hepatitis, hemorrhage, and possible sudden death
- Chronic form: Adult flukes in bile ducts leading to biliary fibrosis, anemia, weight loss, and edema
- Economic loss: Total liver condemnation, reduced carcass weight, lower milk production, and poorer fertility
- Diagnosis: Fecal sedimentation for eggs, ELISA in serum or bulk milk, and slaughterhouse liver inspection
- Treatment: Triclabendazole for all stages, albendazole mainly for adults, and closantel in suitable programs
- Prevalence in Turkey: Roughly 10-60% depending on region, especially in wet grazing areas
2. External Parasites (Ectoparasites)
| Parasite | Clinical Effect | Disease Transmission | Control |
|---|---|---|---|
| Ticks (Ixodidae) | Blood loss, skin damage, stress, and anemia | Vectors of babesiosis, anaplasmosis, and theileriosis | Acaricides by pour-on, dipping, or spray, plus pasture management |
| Flies (Musca, Stomoxys, Haematobia) | Stress, lower DMI, lower milk yield by 10-20%, and hide damage | Mechanical vectors of diseases such as anthrax and BLV | Pour-ons, insecticide ear tags, traps, and hygiene |
| Lice (Linognathus, Haematopinus) | Pruritus, hair loss, and anemia with sucking lice | — | Pour-ons using ivermectin or deltamethrin, or injectable macrocyclic lactones |
| Mange mites (Sarcoptes, Psoroptes, Chorioptes) | Severe itching, crusting, skin thickening, and production loss | — | Macrocyclic lactones such as ivermectin or moxidectin, and amitraz where appropriate |
| Hypoderma spp. | Larval migration causing dorsal nodules and hide damage | — | Macrocyclic lactones, especially in autumn strategic treatment |
3. Anthelmintic Drug Groups
| Drug Group | Active Compounds | Spectrum | Administration | Resistance Status |
|---|---|---|---|---|
| Benzimidazoles (1-BZ) | Albendazole, fenbendazole, oxfendazole | GI nematodes, lungworms, and some cestodes | Oral | Resistance is becoming more common |
| Imidazothiazoles / tetrahydropyrimidines (2-LV) | Levamisole | GI nematodes and lungworms | Oral, SC, or pour-on | Moderate resistance in some systems |
| Macrocyclic lactones (3-ML) | Ivermectin, doramectin, moxidectin, eprinomectin | Broad spectrum against GI nematodes and many ectoparasites | SC, pour-on, or oral depending on formulation | Resistance is rising especially in Cooperia |
| Trematocides | Triclabendazole, closantel, nitroxinil | Fasciola hepatica and related trematode targets | Oral | Triclabendazole resistance exists in some regions |
4. Strategic Treatment Program
Suggested Strategic Program for Turkey
| Season or Period | Target Parasite | Suggested Treatment | Comment |
|---|---|---|---|
| Spring (March-April) | GI nematodes after winter survival and liver fluke | Macrocyclic lactone plus triclabendazole | Ideally before turnout to pasture |
| Mid-summer (July) | GI nematodes during high pasture contamination | Benzimidazole or levamisole in rotation | Useful during periods of heavy challenge |
| Autumn (October-November) | GI nematodes, liver fluke, and Hypoderma | Macrocyclic lactone plus triclabendazole | Before housing and for warble fly control |
| Feedlot entry | GI nematodes and ectoparasites | Macrocyclic lactone by pour-on or SC route | At arrival during the quarantine period |
5. Anthelmintic Resistance Management
Strategies to Slow Resistance Development
- FECRT: Use the fecal egg count reduction test to evaluate efficacy; less than 95% reduction suggests resistance
- Drug rotation: Rotate among major drug groups such as BZ, LV, and ML over time
- Preserve refugia: Leave about 10-20% of the group untreated to maintain a susceptible parasite population
- Targeted treatment: Treat high-burden animals rather than treating the whole herd every time
- Correct dosing: Dose according to the heaviest animal because underdosing selects for resistance
- Pasture management: Use rotational grazing, mixed-species strategies, and pasture rest where feasible
6. Herd-Level Monitoring
| Parameter | Target | Alarm | Measurement |
|---|---|---|---|
| FEC | <200 EPG in adult cattle | >500 EPG | Seasonal monitoring by McMaster technique |
| FECRT | >95% reduction | <90% indicating likely resistance | FEC before treatment and again 14 days later |
| Fasciola bulk-milk ELISA | Negative | Positive | Bulk-milk testing every 6 months where relevant |
| Slaughterhouse liver feedback | <5% condemnation | >15% condemnation | Routine slaughterhouse reports |
7. References
- Charlier, J., et al. (2014). Gastrointestinal nematode infections in adult dairy cattle: Impact on production, diagnosis and control. Veterinary Parasitology, 205(1-2), 56-68.
- Kaplan, R. M. (2004). Drug resistance in nematodes of veterinary importance: A status report. Trends in Parasitology, 20(10), 477-481.
- Schweizer, G., et al. (2005). Estimating the financial losses due to bovine fasciolosis in Switzerland. Veterinary Record, 157(7), 188-193.
- Vercruysse, J., & Claerebout, E. (2001). Treatment vs non-treatment of helminth infections in cattle: Defining the threshold. Veterinary Parasitology, 98(1-3), 195-214.