Composition of the teat canal and intramammary microbiota of dairy cows subjected to antimicrobial dry cow therapy and internal teat sealant

Abstract

Antimicrobial dry cow therapy (DCT) is an important component of mastitis control programs aimed to eliminate existing intramammary infections and prevent the development of new ones during the dry period. However, to what extent the microbiota profiles of different niches of the udder change during the dry period and following administration of DCT remains poorly understood. Therefore, the main objective of the present study was to qualitatively evaluate dynamics of the microbiota of teat canal (TC) and mammary secretions (i.e., milk and colostrum) of healthy udder quarters subjected to DCT using a long-acting antimicrobial product, containing penicillin G and novobiocin, in combination with internal teat sealant. To this end, TC swabs (n = 58) and their corresponding milk (n = 29) and colostrum samples (n = 29) were collected at the time of drying off and immediately after calving from clinically healthy udder quarters of Holstein dairy cows from a commercial dairy farm. All samples were subjected to DNA extraction and high-throughput sequencing of the V1-V2 hypervariable regions of bacterial 16S rRNA genes. Overall, shifts were more pronounced within the microbiota of mammary secretions than the TC. In particular, microbiota of colostrum samples collected immediately after calving were less species-rich compared with the pre-DCT milk samples. Proportions of several bacterial genera belonging to the phylum Proteobacteria, including Pseudomonas, Stenotrophomonas, and unclassified Alcaligenaceae, were enriched within the microbiota of colostrum samples, whereas Firmicutes genera, including Butyrivibrio, unclassified Clostridiaceae, and unclassified Bacillales, were overrepresented in pre-DCT milk microbiota. Apart from shifts in the proportion of main bacterial genera and phyla, qualitative analysis revealed a high degree of commonality between pre-DCT and postpartum microbiota of both niches of the udder. Most importantly, a considerable number of bacterial genera and species commonly regarded as mastitis pathogens or opportunists (or both), including Staphylococcus spp., unclassified Enterobacteriaceae, and Corynebacterium spp., were shared between pre-DCT and postpartum microbiota of mammary secretions. Percentage of shared bacterial genera and species was even higher between pre-DCT and postpartum microbiota of TC samples, suggesting that the DCT approach of the present study had limited success in eliminating a considerable proportion of bacteria during the dry period.

Milk Microbiota: What Are We Exactly Talking About?

“…Taxonomic profiles and alpha diversity were also related to the stage of lactation and varied during the first week of lactation (Derakhshani et al, 2018b). Differences were also observed in clinically healthy Holstein dairy cows between microbiota of the teat canal and mammary secretions (milk or colostrum) at the time of drying off and immediately after calving (Derakhshani et al, 2018c).…”

“…However, a recent study investigated the microbiota composition of human milk collected in a nonaseptic environment, corresponding to "Breastfeeding-associated microbiota of human milk" rather than human milk microbiota (Simpson et al, 2018). Most studies on milk microbiota have used mature milk, but few have investigated colostrum microbiota in human and bovines (Aakko et al, 2017;Lima et al, 2017;Toscano et al, 2017;Derakhshani et al, 2018c). Some studies considered milk collected from only one nipple or teat, whereas others considered pooled milk (Dolci et al, 2014;Chaves Lopez et al, 2016).…”

“…This study was done on a limited number of samples, and further research is required to clarify whether live microorganisms are present in milk inside a healthy mammary gland. Apart from milk, a limited number of studies have explored the microbiota associated to the bovine teat skin or teat apex (Gill et al, 2006;Braem et al, 2012;Verdier-Metz et al, 2012;Frétin et al, 2018), or the internal teat by sampling foremilk and swabbing the teat canal (Falentin et al, 2016;Derakhshani et al, 2018c). Similarly, only few reports are available about the microbiota associated with the mammary gland tissues in human and mouse (Urbaniak et al, 2014;Treven et al, 2015).…”

“…A number of studies have characterized the milk microbiota mainly in human and cows and mainly using cultureindependent approaches; all of them describe a complex and diverse community (Cabrera-Rubio et al, 2012;Oikonomou et al, 2014;Addis et al, 2016;Murphy et al, 2017;Derakhshani et al, 2018c). As an illustration, Murphy et al studied 10 mother-infant pairs and identified over 207 genera in human milk microbiota.…”

“…The authors suggest that bacterial communities are dynamic and that the antimicrobially induced disturbance of milk microbiota is reversed by the time that cows start a new lactation. Likewise, antimicrobial DCT combining penicillin G and novobiocin in internal teat sealant showed that a considerable number of bacterial genera, including those commonly regarded as mastitis pathogens, were common between the pre-DCT and postpartum microbiota, suggesting a high resilience of the mammary microbiota after exposure to antimicrobials during the dry period (Derakhshani et al, 2018c). Another possible explanation of these findings could be that a large proportion of what is described as the milk microbiota is DNA from bacteria that are already dead and will therefore not be affected by antibiotic therapy.…”