The microbiome of the bovine mammary gland: going further in our understanding of this complex issue

Abstract

In recent years, with the advancement of molecular techniques, there has been a growing search for communities of commensal microorganisms, due to the fact that many of these populations have the capacity to prevent or favor many diseases, also focusing on the bovine mammary gland. The previously accepted consensus on the sterility of the mammary gland has been challenged as a result. Some authors assume that the mammary gland has its own microbiota, while others argue that it is sterile. In that respect, the objective of the present project is: 1) to define the best technique to collect material for mammary gland microbiome analysis; 2) to evaluate the relationship between the integrity of the teat canal and the microbiota of the mammary gland of prepartum heifers, and its effect on udder health during the postpartum period; 3) to investigate the existence of commensal microorganisms in prepartum heifers; 4) to investigate the relationship between the teat apex and the milk microbiome; and 5) to explore of the association between the rumen and fecal microbiota, and udder health. For these reasons, this study will be divided into two phases. In the first phase, the opening of the teat canal during the prepartum period in dairy heifers will be evaluated by visual inspection and ultrasonographic examination at 21 days before parturition. At this moment, mammary gland secretion will be collected for microbiological and high-throughput sequencing of the 16SrRNA analyses. Furthermore, postpartum colostrum and milk samples will be collected at five moments (M1: at the day of parturition; M2: three; M3: seven; M4: 15 and M5: 30 days postpartum) for microbiological analysis and somatic cell counting. All clinical mastitis cases will also be recorded and sampled during this period. At seven days in lactation, we will compare four milk sampling techniques using milk samples from dairy heifers (the same animals used at 21 days before parturition), to define the best method of milk collection for the microbiome analysis, as follows: a) traditional collection, as recommended by the National Mastitis Council (NMC); b) the collection of milk through the use of a cannula; c) the collection of milk samples using a vacuum collection system directly from the mammary gland cistern; and d) the collection of milk samples using a vacuum collection system directly from the alveolar region of the mammary gland guided by ultrasound. At the same time, teat apex swabs, fecal and rumen samples will also be collected and subjected to high-throughput sequencing of the 16SrRNA analysis. In the second phase, the existence of microbial populations in nulliparous heifers will be investigated through mammary biopsies and high-throughput sequencing of the 16SrRNA analysis. (AU)