HAEMATOLOGICAL INVESTIGATION OF A MULTIPLE CASE LEUCOSIS HERD

Area of Science:

• Veterinary Medicine
• Animal Oncology
• Epidemiology

Background:

• Lymphosarcoma causes significant mortality in adult cattle.
• Persistent lymphocytosis (PL) has been associated with lymphosarcoma in dairy herds.
• A Queensland dairy herd experienced recurrent deaths attributed to lymphosarcoma.

Purpose of the Study:

• To identify cattle with persistent lymphocytosis (PL) in a dairy herd with a history of lymphosarcoma.
• To assess the impact of culling on the prevalence of lymphocytosis.
• To evaluate the association between lymphocytosis and lymphosarcoma development.

Main Methods:

• Regular blood sampling of adult cattle over a 4-year period.
• Hematological analysis to identify persistent lymphocytosis (PL).
• Culling of animals identified with hematological abnormalities.

Main Results:

• Twenty-one of 94 eligible cattle (sampled ≥6 times) exhibited persistent lymphocytosis (PL).
• Initial lymphocytosis prevalence was 27%, reduced to 5.3% after 18 months of culling.
• Cessation of culling led to a gradual increase in lymphocytosis prevalence.
• Four adult cattle deaths from lymphosarcoma occurred within the first 18 months; two had lymphocytosis and two had lymphoblastic leukemia.
• A calf from a cow with lymphoblastic leukemia also developed the condition and lymphosarcoma by 6 months of age.

Conclusions:

• Hematological monitoring can identify cattle at risk of developing lymphosarcoma, even without definitive histological evidence.
• Culling strategies targeting lymphocytosis can reduce herd prevalence.
• Ongoing surveillance is crucial for managing lymphosarcoma in susceptible dairy herds.