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Dott. Alessandro Bellato

Phd thesis

Modelling the risk of bacterial infections, within the framework of the evaluation of the health and welfare of dairy cows in the Northern Apennines

Mastitis still is the most common cause of morbidity in adult dairy cows, jeopardizing animal health, welfare, and productivity. Up to 90% of mastitis cases are caused by microorganisms, but several other factors affect the cow’s ability to deal with the infection. Therefore, many risk factors need to be evaluated to estimate the actual risk of mastitis. For this purpose, dairy herd improvement program (DHI) data, which are a large amount of milk analysis results often unexploited for epidemiological purposes, offer the opportunity not only to precisely estimate the burden of diseases, but also the risk factors and the relationship with other health problems. However, part of the risk cannot be estimated by DHI data, as it depends on unmeasured factors that act at the herd level, like animal husbandry and herd management. Quantifying this unmeasured quota of risk allows to produce adjusted health indicators for each herd which can be used as a screening tool for animal welfare. Moreover, estimating health indicators is possible to benchmark the herds and explore their geographical distribution to discover that mastitis cases, in Piedmont, are more frequent in mountain settings.

To face mastitis, an accurate diagnosis of bacterial and algal pathogens is essential as it allows to implement the adequate control and eradication strategy. However, in mountain areas, the access to veterinary and agricultural services might be limited due to the rarefaction of human settlement and the abandonment of dairy farming. This lack of services compromises the profitability of the remaining dairy operation. However, not all mountain areas are facing abandonment, and thriving areas exist at a short distance from areas where few dairy herds remain. The differences between the two types of areas are not evidently linked to farm management, but a neat diversification is seen with the type of mastitis pathogens involved in intramammary infections. In areas where few herds exist, contagious agents are the most part, while environmental and opportunistic infections are the most part in thriving areas.

Contagious mastitis pathogens are present not only in rural areas, but also theire prevalence is increasing in intensive dairy herds of northern Europe. This is due to the change in their epidemiology as contagious agents like Streptococcus aalactiae become able to spread through environmental contamination. Such changes require a more detailed diagnosis to implement an adequate treatment and control plan, but genetic methods are usually time-consuming and expensive. In this context, I worked on the development of MALDI-TOF and FTIR spectroscopy methods to rapidly type S. agalaactiae and Staphylococcus aureus.


Research activities

The Italian Breeder Association (AIA) test-day records of almost 90% of Piedmontese dairy cows from 2015 to 2020 were analysed. From those data, several health indicators (HI) were calculated to assess the health status of dairy herds in Piedmont. At the cow level, risk factors for each HI were precisely estimated; at the herd level, adjusted measures of each HI were produced and used to explore their geographic distribution, comparing herds in mountains and plains, and assessing local aggregation. Also, HI were tested as a screening method to identify herds at risk of poor welfare (i.e., herds with the lowest welfare evaluation score).

Between April and September 2021, dairy herds of three Apennine areas were sampled. Bacteriological identification was performed using MALDI-TOF spectroscopy and antimicrobial susceptibility was assessed determining the minimum inhibitory concentration. The prevalence of different types of bacteria was estimated adjusting for cow individual factors. Mass-spectra analysis showed that pathogens tend to cluster at the herd level.

During sampling, information about husbandry systems, biosecurity measures and antibiotic use were collected by interviewing farmers. That information was used to assess which were the main differences between the areas.

In collaboration with anthropologist Sarah Henry Whitaker, a non-structured interview about animal welfare and milking hygiene was set up as a follow-up study for certain herds. Scheduled activity for the second year foresees the involvement of a small number of breeders in a training program aimed at improving udder health.

Last update: 12/12/2023 01:09

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