Paratuberculosis impairs productivity of infected dairy cows because of reduced milk production and fertility and enhanced risk of culling. The magnitude of the milk yield depression in individual cows is influenced by factors such as parity, the stage of the disease and the choice of test used. The objectives of this case-control study were to substantiate the influence of the different levels of the within-herd prevalence (WHP) on individual milk yield of fecal culture (FC)-positive cows (FC+) compared with FC-negative herd-mates (FC−), and to estimate the magnitude of the deviation of the milk yield, milk components and somatic cell count (SCC) in an FC-based study. Of a total of 31 420 cows from 26 Thuringian dairy herds tested for paratuberculosis by FC, a subset of 1382 FC+ and 3245 FC− with milk recording data were selected as cases and controls, respectively. The FC− cows were matched for the same number and stage of lactation (±10 days in milk) as one FC+ from the same herd. Within a mixed model analysis using the fixed effects of Mycobacterium avium ssp. paratuberculosis (MAP) status, lactation number, days in milk, prevalence class of farm and the random effect of farm on milk yield per day (kg), the amount of fat and protein (mg/dl) and lactose (mg/dl) as well as the SCC (1000/ml) were measured. On the basis of least square means, FC+ cows had a lower test-day milk yield (27.7 ± 0.6 kg) compared with FC− (29.0 ± 0.6 kg), as well as a lower milk protein content and a slightly diminished lactose concentration. FC status was not associated with milk fat percentage or milk SCC. In FC+ cows, reduction in milk yield increased with increasing WHP. An interaction of FC status and farm was found for the test-day milk yield, and milk protein percentage, respectively. We conclude that the reduction in milk yield of FC+ cows compared with FC− herd-mates is significantly influenced by farm effects and depends on WHP class. Owners of MAP-positive dairy herds may benefit from the reduction in WHP not only by reducing number of infected individuals but also by diminishing the individual losses in milk production per infected cow, and therefore should establish control measures.

BackgroundParatuberculosis caused by Mycobacterium avium subsp. paratuberculosis (MAP) is difficult to control due to a long phase of clinically non-apparent (latent) infection for which sensitive diagnostics are lacking. A defined animal model for this phase of the infection can help to investigate host-MAP interactions in apparently healthy animals and identify surrogate markers for disease progress and might also serve as challenge model for vaccines. To establish such a model in goats, different age at inoculation and doses of oral inoculum of MAP were compared. Clinical signs, faecal shedding as well as MAP-specific antibody, IFN-γ and IL-10 responses were used for in vivo monitoring. At necropsy, about one year after inoculation (pi), pathomorphological findings and bacterial organ burden (BOB) were scored.ResultsMAP infection manifested in 26/27 inoculated animals irrespective of age at inoculation and dose. Clinical signs developed in three goats. Faecal shedding, IFN-γ and antibody responses emerged 6, 10–14 and 14 wpi, respectively, and continued with large inter-individual variation. One year pi, lesions were detected in 26 and MAP was cultured from tissues of 23 goats. Positive animals subdivided in those with high and low overall BOB. Intestinal findings resembled paucibacillary lesions in 23 and multibacillary in 4 goats. Caseous and calcified granulomas predominated in intestinal LNN. BOB and lesion score corresponded well in intestinal mucosa and oGALT but not in intestinal LNN.ConclusionsA defined experimental infection model for the clinically non-apparent phase of paratuberculosis was established in goats as suitable basis for future studies.

Using well established metabolic parameters, this study aimed to substantiate differences in protein and energy metabolism between Mycobacterium avium subspecies paratuberculosis (MAP) positive and negative dairy cows tested by faecal culture. A total of 227 MAP-positive and 239 MAP-negative German Holstein cows kept in 13 MAP-positive dairy herds were selected for metabolic testing. The serum concentrations of total protein (TP), bilirubin, cholesterol and betahydroxybutyrate were measured as well as the activities of Glutamate-Dehydrogenase (GLDH) and Aspartate-Aminotransferase. MAP-positive cows were characterised by a decreased mean TP (66.5 g/l) compared to the MAP-negative controls (73.2 g/l). Mean log10 GLDH activities tended to be higher in MAP-positive than MAP-negative cows. Concerning TP, there was a significant interaction between MAP status and farm. Within four farms, the difference between MAP-positive and MAP-negative animals differed significantly, while in the other farms this difference was not significant. It is concluded that a decreased TP and an increased GLDH indicate alterations in protein metabolism. These findings suggest an enhanced liver cell turnover in MAP-positive cows. The results contribute to an understanding of the metabolic alterations in MAP-positive dairy cows.