Infected dams, which may or may not be exhibiting signs, can pass the disease to calves while nursing through their colostrum and milk. Because of its mode of spreading, Johne's must be considered a herd problem, as well as an individual animal problem. Obvious clinical signs of Johne s include weight loss, diarrhea and lower milk production. Some animals continue to eat normally. Diarrhea may begin intermittently then progress to chronic, usually without a fever.
Some infected animals appear unthrifty and have a swelling under the jaw.
These signs are similar to other diseases and conditions, making a veterinarian s diagnosis necessary. Symptoms usually first surface when an animal is two years old, following a physical stress like calving. However, visible signs of Johne s may not appear for 10 years or more. The age of the animal at exposure and the number of bacteria ingested determine when the symptoms of the disease develop. Research indicates animals maintained under better feed and husbandry conditions tolerate infection better.