Review of the bacterial composition of healthy milk, mastitis milk and colostrum in small ruminants

Bacterial infections are the cause of many reproductive disorders of economic importance, such as mastitis, in livestock. Unfortunately, very little is known about the microbiota and the changes occurring during an infection state in small ruminants. The sequencing of regions of the 16S rRNA gene, is the useful tool to describe the whole dairy microbiome. Using this technique, studies have identified various phyla such as Firmicutes, Actinobacteria, Proteobacteria, Bacteroidetes, Fusobacteria and Cyanobacteria; and also several genera from raw milk of small ruminants. Nevertheless, there does not seem to be a consensus on the predominant genera nor phyla, even within the same breed. There is a lack of information about the mammary microflora in meat-oriented breeds, and about the microflora of colostrum and mastitis milk. Further studies comparing the microbiota between artificial and natural lactations and between healthy and mastitis milk are necessary. Considering the concerns arising from the use overuse of antibiotic therapy in Veterinary Medicine, it would be interesting to develop alternative strategies for the control of mastitis. Probiotics, such as lactic acid bacteria (LAB), have proven to be an interesting antibiotic-free strategy. Therefore, their presence in the dairy microflora of small ruminants and their interactions with other bacteria, such as mastitis-causing pathogens, should be scrutinized, given that the efficacy of probiotics increase when the bacterial strains used are specific to their host. •The bacterial composition of small ruminants' milk is highly variable due to several factors such as environment and the animal itself.•The balance of the microbiota is essential for the animal health, disruptions can lead to an infection.•Metagenomic studies are essential for the understanding of the microbiota of the mammary gland in small ruminants.•The role of lactic acid bacteria in an infection state is important as it can constitute an alternative to antibiotic therapy.