Cow disease prevention (tuberculosis)
Tuberculosis in Cows: Prevention and Control
Bovine tuberculosis is a chronic infectious disease caused by *Mycobacterium tuberculosis*, which affects both humans and livestock. It is characterized by the formation of granulomas in various tissues and organs, leading to progressive weight loss, weakness, and, in severe cases, death.
The pathogen is divided into three main types: human, bovine, and avian. Among these, the bovine type is most commonly responsible for infections in cattle. The bacteria are long, rod-shaped, acid-fast, Gram-positive organisms that do not form spores or move. They can survive in exudates and feces for several days. Effective disinfection methods include using 2% to 3% sodium hydroxide solutions.
Infected animals serve as the primary source of infection. The bacteria can be transmitted through respiratory secretions, feces, urine, milk, or other bodily fluids. Cows can become infected when they come into contact with diseased animals or contaminated feed, water, or equipment. Poor management practices—such as overcrowding, poor ventilation, lack of nutrition, and unhygienic conditions—can significantly increase the risk of disease spread.
Once infected, cows may show a range of symptoms depending on the affected organs. Early signs include a dry, hacking cough that progresses to a wet, painful cough, along with nasal discharge and increased breathing rate. Physical examination might reveal abnormal lung sounds and chest dullness. Affected animals often experience weight loss, anemia, and reduced milk production.
In some cases, the disease may affect the udder, causing painless hard swellings in the lymph nodes and changes in milk quality. Reproductive issues such as abnormal vaginal discharge, uterine enlargement, and infertility may also occur. Intestinal involvement leads to swollen mesenteric lymph nodes, loss of appetite, and irregular bowel movements, including diarrhea mixed with mucus or pus.
Diagnosis typically involves the tuberculin skin test, a standard method used in dairy farming. Two types of tuberculin are commonly used: old tuberculin (OT) and purified protein derivative (PPD). For OT testing, the injection site is usually the middle of the neck in adult cattle, while calves receive it on the front of the shoulder. After injection, reactions are observed at 72 and 120 hours. A positive reaction is defined as a swelling of 8mm or more, while a suspicious result shows less than 8mm but more than 5mm. Negative results show minimal or no swelling.
For PPD testing, the same area is used, and a reaction of more than 4mm indicates a positive result. If the response to avian tuberculin is greater than to bovine tuberculin, the animal is considered negative for bovine tuberculosis.
Prevention is key. Regular quarantine inspections, especially in spring and autumn, help identify and isolate infected animals. Infected cattle should be culled, while asymptomatic ones may be isolated or removed. Proper sanitation, including the use of 20% bleach or 5% lye for disinfection, is essential. New animals must undergo quarantine before being introduced to the herd.
Calves from infected cows are separated early, given colostrum for a few days, and then moved to a transit station. They undergo three rounds of tuberculosis testing at 20–30 days, 100–120 days, and 160–180 days of age. Only those testing negative in all three tests are allowed into healthy groups. This approach ensures effective control and reduces the risk of spreading the disease.
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