Correct Option: A. Abortion Detailed Explanation: Brucellosis is a bacterial infection caused by the Brucella species, which primarily affects livestock, including cattle. The most significant and notable symptom of brucellosis in cattle is abortion, particularly in the later stages of pregnancy. Here’s a step-by-step breakdown of why this is the correct answer:

1. Understanding Brucellosis:
2. Brucellosis is a zoonotic disease, meaning it can be transmitted from animals to humans. In cattle, the disease is primarily caused by Brucella abortus.
3. The bacteria can infect various organs, but they have a particular affinity for the reproductive system.
4. Impact on Pregnancy:
5. Infected pregnant cows often experience abortion, typically occurring in the last trimester. This is due to the bacteria's ability to invade the placenta and cause inflammation, leading to fetal death.
6. The abortion can occur suddenly and may be the first sign of the disease in a herd, making it a critical symptom for diagnosis.
7. Consequences of Abortion:
8. The loss of the fetus not only affects the individual animal but can also have significant economic implications for farmers due to loss of potential offspring and the costs associated with managing the disease in the herd.
9. Other Symptoms:
10. While brucellosis can cause other symptoms, such as swollen testes, lameness, and swollen joints, these are not as definitive or as commonly observed as abortion.

Why Other Options Are Incorrect:

• B. Swollen Testes:
• Swollen testes can occur in bulls infected with brucellosis, but this symptom is less common and does not occur in cows. It is not a primary indicator of the disease and is more associated with other conditions, such as epididymitis.
• C. Lameness:
• Lameness can be caused by various factors, including injuries or other diseases. While it may occur in some cases of brucellosis, it is not a hallmark symptom and is not specific to this disease.
• D. Swollen Joints:
• Swollen joints can be a symptom of several conditions, including arthritis or other infections. Like lameness, it is not a specific or primary symptom of brucellosis and can be seen in many other diseases affecting cattle.

Summary of Key Points:

• The most important symptom of brucellosis in cattle is abortion, particularly in the later stages of pregnancy.
• Brucella bacteria target the reproductive system, leading to significant economic losses for farmers.
• Other symptoms like swollen testes, lameness, and swollen joints are less specific and not as commonly associated with brucellosis.
• Understanding the primary symptoms of diseases like brucellosis is crucial for effective diagnosis and management in agricultural settings.

This thorough understanding of brucellosis and its symptoms is essential for anyone studying agricultural science, particularly in the context of livestock health management.