The effect of Mycobacterium avium ssp. paratuberculosis infection on clinical mastitis occurrence in dairy cows

Abstract

Endemic diseases can be counted among the most serious sources of losses for livestock production. In dairy farms in particular, one of the most common diseases is Johne's disease, caused by Mycobacterium avium ssp. paratuberculosis (MAP). Infection with MAP causes direct costs because it affects milk production, but it has also been suspected to increase the risk of clinical mastitis (CM) among infected animals. This might contribute to further costs for farmers. We asked whether MAP infection represents a risk factor for CM and, in particular, whether CM occurrences were more common in MAP-infected animals. Our results, obtained by survival analysis, suggest that MAP-infected cows had an increased probability of experiencing CM during lactation. These results highlight the need to account for the interplay of infectious diseases and other health conditions in economic and epidemiological modeling. In this case, accounting for MAP-infected cows having an increased CM occurrence might have nonnegligible effects on the estimated benefit of MAP control.

Association of paratuberculosis sero-status with milk production and somatic cell counts across 5 lactations, using multilevel mixed models, in dairy cows

“…Positive significant associations between SCC and MAP have been reported in several previous studies (Baptista et al, 2008;McNab et al, 1991;Pritchard et al, 2017). The association between MAP and clinical mastitis (Rossi et al, 2017), subclinical mastitis (Pritchard et al, 2017), and higher culling rates (Smith et al, 2010) has also been previously documented. Our models showed a significant association between lnSCC and MAP POS CS, which is dependent from lactation number and farm.…”

“…It is noteworthy that studies about the dilution factor are based on individual testday measurements and are intended to draw inferences, which was not the case in our study. In line with other authors (Pritchard et al, 2017;Rossi et al, 2017), we did not consider such correction in the models. We considered that the comparability between the 2 groups should not be affected, as the dilution effect would be present in both groups of cows in the same manner.…”

“…The association between SCC and MAP was expected, as the immune system from cows affected by MAP should be progressively weakened, resulting in higher susceptibility to udder infection (Pritchard et al, 2017). Recently, Rossi et al (2017) reported that cows with progressive and nonprogressive infection had higher average SCC than MAP-negative animals, and that latent animals had higher average SCC than MAP-negative animals. Pritchard et al (2017), in a study where cows were classified as low-, medium-and high-risk based on multiple MAP testing, found that the log-transformed lactationaverage SCC from medium-and high-risk cows was higher than for low-risk cows, and differences were in almost all cases significant.…”

Mastitis risk effect on the economic consequences of paratuberculosis control in dairy cattle: A stochastic modeling study

“…In the NM scenario, it was assumed that CM cases were excluded in the model. In the MA and NMA scenarios, CM occurred in susceptible adults at rate ψ , the annualized risk, and in MAP infected adults at rate ξ Iψ , where ξ I is the hazard ratio 1.89 [34].…”

“…One factor that none of these studies addressed is the role of MAP infection in susceptibility to other infections. For example, higher mastitis incidence has been found in MAP positive farms in two different studies [32,33], and Rossi et al [34] found that MAP-infected animals had significantly higher rates of clinical mastitis. As clinical mastitis is one of the most economically important diseases of dairy herds, a positive association between MAP infection and mastitis could greatly increase the cost-effectiveness of MAP and mastitis control.…”