No abstract

Paratuberculosis, which is also known as Johne's disease, is a chronic, progressive enteric disease of ruminants caused by infection with Mycobacterium paratuberculosis. Cattle become infected with M. paratuberculosis as calves but often do not develop clinical signs until 2 to 5 yr of age. The clinical disease is characterized by chronic or intermittent diarrhea, emaciation, and death. Although animals with clinical disease are often culled from the herd, animals with subclinical paratuberculosis may cause economic losses because of reduced milk production and poor reproductive performance. Although the economic impact of paratuberculosis on the national cattle industry has not been determined, it is estimated to exceed $1.5 billion/yr. The diagnosis of subclinical paratuberculosis is difficult. Bacteriologic culture is the most definitive method of diagnosis, but culture is time consuming and labor intensive. Serological assays are not very useful because animals do not develop an antibody response until the clinical stages of disease. Development of assays to measure cell-mediated immunity is critical to accurate detection of paratuberculosis in subclinically infected animals. Although not considered a zoonotic agent, M. paratuberculosis has been identified in intestinal biopsy tissue from patients with Crohn's disease, an inflammatory enteritis in humans. Currently, the potential human health risk is being addressed by research evaluating pasteurization of dairy products in the US.

The objective of this paper is to study shedding patterns of cows infected with Mycobacterium avium subsp. paratuberculosis (MAP). While multiple single farm studies of MAP dynamics were reported, there is not large scale meta-analysis of both natural and experimental infections. Large difference in shedding patterns between experimentally and naturally infected cows were observed. Experimental infections are thus probably driven by different pathological mechanisms. For further evaluations of shedding patterns only natural infections were used. Within such infections, the transition to high shedding was studied as a proxy to the development of a clinical disease. The majority of studied cows never developed high shedding levels. Those that do, typically never reduced their shedding level to low or no shedding. Cows that eventually became high shedders showed a pattern of continuous shedding. In contrast, cows with an intermittent shedding pattern had a low probability to ever become high shedders. In addition, cows that start shedding at a younger age (less than three years of age) have a lower hazard of becoming high shedders compared to cows starting to shed at an older age. These data suggest the presence of three categories of immune control. Cows that are intermittent shedders have the infection process under control (no progressive infection). Cows that start shedding persistently at a young age partially control the infection, but eventually will be high shedders (slow progressive infection), while cows that start shedding persistently at an older age cannot effectively control the infection and become high shedders rapidly.

No abstract

Fumonisins are myocotoxins produced by Fusarium moniliforme and F. proliferatum, common molds of corn in North America. The toxin is at especially high concentrations in corn screenings. Fumonisins are toxic to swine and horses, but effects of these toxins in cattle have not been evaluated. This experiment was conducted to determine the effects in cattle of feeding fumonisins at levels known to be toxic to swine and horses. A total of 18 crossbred feeder calves were fed diets containing fumonisins at 15, 31, or 148 micrograms/g for 31 d. Feed consumption, weight gain, complete blood count, serum clinical chemistries, and an immune function profile were done on d -3, 4, 10, 17 and 31 relative to the start of fumonisin feeding. There was no treatment-related effect on feed intake or weight gain, but feed containing 148 micrograms/g of fumonisins seemed to be less palatable than other feeds. Significant increases in serum aspartate amino transferase, gamma glutamyl transpeptidase, lactate dehydrogenase, bilirubin, and cholesterol occurred from d 10 through 31. Mild microscopic liver lesions were present in two calves fed at the highest fumonisin level. Lymphocyte blastogenesis was significantly impaired at the end of the feeding period in the group given the highest dose. Other measures of immune function were not affected significantly. Fumonisins are capable of causing changes in liver function and in some measures of immune function. However, cattle seem to be relatively less susceptible to fumonisins present naturally in grains than either swine or horses.