Epidemiology of udder health in organic dairy cows

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Mastitis is a disease that affects the mammary gland of cows, which is caused by an inflammatory response that can be trigged by an infectious or non-infectious cause. Most of the times, it is caused by the entrance of a pathogen through the teat and can manifest visual signs or only be diagnosed through laboratorial tests. This disease is responsible for most of economic losses for conventional dairy producers, and some of the impacts caused by it are lower milk production, impaired fertility, and increased rates of culling. Although the importance of mastitis is more established for conventional dairies, it is also capable to cause detrimental impacts in organic dairies. The objective of this thesis is to provide a better understanding of the epidemiology of mastitis in certified organic dairies. In the first study, the objective was to evaluate whether SCM diagnosed during the first month of lactation was associated with SCC linear score dynamics, milk production, fertility and culling of dairy cows in organic farms. In this study, the results were that cows diagnosed with SCM during the first month of lactation produced less milk than non-SCM cows. Cows with SCM had elevated SCC linear score during the previous lactation and throughout the subsequent months of lactation when compared to cows without SCM. The impact of SCM on linear scores of SCC was more pronounced in multiparous than primiparous cows. Subclinical mastitis during the first month of lactation did not affect the likelihood of pregnancy during the first 300 DIM. Lastly, cows with SCM in the first month were more likely to die or be culled during the 300 days of lactation than cows without SCM. In conclusion, we observed that elevated SCC in the first month of lactation has detrimental impacts on milk yield and survivability of dairy cows in USDA-organic herds, but it did not affect reproductive performance. We demonstrated that cows with SCM diagnosed in the first month of lactation continued to have elevated SCC linear scores throughout their entire lactation, and that elevated SCC was carried over from the previous lactation. In the second study, the objectives were to identify risk factors associated with intramammary infections during the 1st week of lactation in primiparous organic dairy cows, and to evaluate the association of those risk factors with somatic cell count (SCC) linear scores and milk yield (MY) in early lactation. As results, this study could provide that cows with ML at 1st week postpartum were at 3.42 greater odds of IMI, while UE at 1 week prior to calving tended to increase in 1.86 the odds of IMI. Cows with prepartum BCS ≥ 3.75 were at 3.12 greater odds of IMI. Cows with ML in the 1st week of lactation had increased SCC and lower milk production in the 2nd month of lactation, while UE at 1-week prepartum tended to be associated with greater SCC. Therefore, managing prepartum BCS, UE and ML at early postpartum can aid in the control of IMIs in heifers in organic dairies. In conclusion, this thesis helps the organic community to understand better the epidemiology of mastitis in their dairies and it provides information that could be useful in the development of methods to control, treat and prevention of mastitis in organic and also conventional cows.

Mastitis, Organic Dairy