Investigating the role of biotic and abiotic factors in modulating bovine mammary gland microbiota: potential implications for udder health and mastitis susceptibility
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Date
2018-07-25
Authors
Derakhshani, Hooman
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Abstract
In the context of bovine mammary gland (MG), the relationship between cow and microbes has been traditionally viewed strictly from the perspective of host-pathogen interaction, where intramammary infections (IMIs) by pathogenic microorganisms result in the triggering of inflammatory responses (i.e. mastitis). This traditional view has been confronted by the results of recent metagenomic studies indicating that milk collected from clinically healthy MGs can harbor diverse bacterial groups, the vast majority of which have not been previously associated with mastitis. These observations have given rise to the concept of "commensal mammary microbiota", the ecological properties of which can have important implications for udder health. In this thesis, we evaluated the potential contribution of different biotic factors, including those associated with host (such as parity, stage of lactation, teat end hyperkeratosis, and genetic traits) as well as microbe-microbe relationships, in shaping the overall structure of mammary microbiota. We observed that mammary microbiota changes dramatically at different stages of lactation, particularly during the transitional shift from colostrum to milk. Among biotic factors, we observed that interrelationships among microbiota play an important role in shaping the overall structure of the community. In particular, we identified potential foundation taxa that made disproportionately large contribution to the overall diversity of the milk microbiota. In addition, we identified an important genetic trait of the cows, the polymorphism of the exon 2 of BoLA-DRB3.2 locus, which can modulate the microbiota profile of intramammary secretions. With respect to the potential influence of abiotic factors, we monitored the peripartal dynamics of teat canal and intramammary microbiota following administration of blanket antimicrobial dry-cow therapy. Our results indicated that although blanket dry-cow therapy could alter the composition of mammary microbiota, a high degree of commonality existed between the microbiota profiles of pre- and post-calving sampling time points. This implies that the success of blanket dry-cow therapy in eliminating chronic and new IMI is limited. Collectively, our results highlight the need to view the microbiota of teat canal and intramammary secretions as interconnected niches of a highly complex microbial ecosystem, the composition of which can be influenced by several biotic and abiotic factors.
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Keywords
Mastitis, Mammary gland microbiota, Dairy cow