Abstract
Bovine paratuberculosis (PTB) causes major economic losses to dairy farmers because of decreased milk production, poor body condition, weight loss and early culling. The aim of this study was to evaluate the effect of Mycobacterium avium subspecies paratuberculosis (MAP) infection on carcass weight and age at slaughter in Friesian cattle. A total of 1,014 adult cows slaughtered at two local abattoirs in the Basque Country were included in this study. MAP infection was determined by different methods: indirect ELISA on blood samples, detection of MAP in tissues by culture and real time PCR (rtPCR), and histopathological examination. Serial and parallel interpretations of these methods were also considered for setting the upper and lower infection rates. MAP infection was confirmed by at least one test in 58.9% of animals. Most infected cows were detected by histopathology (46.9%) and rtPCR (29.6%). Overall estimates of carcass mean weight losses ranged from 3.7% for cases identified by the presence of microscopic specific PTB inflammatory lesions to 12.4% for cases with positive results in the paratuberculosis antibody ELISA test. Isolation of high bacterial loads in tissues and occurrence of diffuse granulomatous enteritis were associated with the highest weight loses, 22.2% and 26.0% respectively. The life expectancy of seropositive cows and those showing diffuse lesions was reduced by nearly one year compared to that of non-infected ones. Our results provide consistent evidences of PTB effect on the reduction of slaughter weight and lifespan of dairy cows, which could be considered as surrogates of clinical disease.
Highlights
Paratuberculosis (PTB) or Johne’s disease (JD) is a chronic granulomatous enteritis caused by Mycobacterium avium subspecies paratuberculosis (MAP) that affects both domestic and wild ruminants all over the world, and for which currently there is not known an efficient treatment (Chiodini et al, 1984; Fecteau & Whitlock, 2011).It is generally accepted that paratuberculosis infection occurs within the first 6-12 months of life, mainly by ingestion of milk, water or food contaminated with faeces containing viable MAP bacilli from infectious animals
Results from this study support previous findings suggesting that MAP infection in adult dairy cattle leads to economic losses because of decreased mean slaughter weight and reduced lifespan
Our study found that adult cows showing high mycobacterial loads in tissues or advanced granulomatous inflammatory lesions consistent with PTB had reduced slaughter weights in comparison with the individuals testing negative to these tests; 22.2% and 26.0%, respectively
Summary
Paratuberculosis (PTB) or Johne’s disease (JD) is a chronic granulomatous enteritis caused by Mycobacterium avium subspecies paratuberculosis (MAP) that affects both domestic and wild ruminants all over the world, and for which currently there is not known an efficient treatment (Chiodini et al, 1984; Fecteau & Whitlock, 2011).It is generally accepted that paratuberculosis infection occurs within the first 6-12 months of life, mainly by ingestion of milk, water or food contaminated with faeces containing viable MAP bacilli from infectious animals. Clinical disease typically appears between 2 and 5 years of age (first and third calving) and is characterized by intermittent diarrhea, poor body condition and decreased milk production, leading to premature culling and death (Chiodini et al, 1984; Stabel 1998). The economic losses caused by bovine PTB have been estimated to be higher than those for other bovine diseases such as bovine viral diarrhea, enzootic bovine leucosis and neosporosis (Chi et al, 2002). The economic consequences of these two items have been estimated to account for nearly 70% of overall direct economic losses occurring in MAP infections (Ott et al, 1999; Groenendaal et al, 2002). Some researchers have suggested that PTB is associated with increased mortality rates, higher infertility rates (Merkal et al, 1975; Buergelt & Duncan, 1978; Johnson-Ifearulundu et al, 1999), greater susceptibility to other secondary pathologies such as mastitis (Buergelt & Duncan, 1978) and decreased slaughter value
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