Milk microbiome in the first month of lactation and at weaning from ewes supplemented with zinc pre- and postpartum

Authors: KNUTH, RYAN - University Of Wyoming; PAGE, CHAD - University Of Wyoming; STEWART, WHITNEY - University Of Wyoming; HUMMEL, GWENDOLYNN - University Of Wyoming; WOODRUFF, KELLY - University Of Wyoming; WHALEY, JAELYN - University Of Wyoming; SPRINGER, ALEXIS - University Of Wyoming; AUSTIN, KATHLEEN - University Of Wyoming; Murphy, Thomas - Tom; BISHA, BLEDAR - University Of Wyoming; CUNNINGHAM-HOLLINGER, HANNAH - University Of Wyoming

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Mastitis is an inflammation of the mammary tissue due to bacterial infection and has economic and welfare implications in both clinical and subclinical states. However, relatively little is known about the impacts of breed and diet on the milk microbiome of sheep. The aim of this research was to describe the microbial diversity and taxonomy of milk collected from clinically healthy ewes of two distinct breeds (Rambouillet and Hampshire) receiving two dietary zinc concentrations (1x and 3x currently recommended levels). Milk was collected from ewes during the first 3 weeks of lactation and at lamb weaning. In early lactation, milk from Hampshire ewes had greater microbial diversity than milk from Rambouillet ewes. Additionally, milk from ewes fed at 1x zinc levels had a reduced rate of microbial compositional change in early lactation than those fed at 3x levels. These results support that milk is not a sterile bodily fluid and its microbial population is variably affected by breed and dietary zinc concentration. Findings from the current study provide important foundational insights into factors contributing to mammary gland health and can guide future genetics and management efforts to reduce the incidence of mastitis.

Technical Abstract: Mastitis is an important disease with economic and welfare implications in both clinical and subclinical states. The aim of this research was to sequence the hypervariable V4 region of the 16S rRNA gene to describe the microbial diversity and taxonomy of milk from clinically healthy ewes (Rambouillet, WF = 9; Hampshire, BF = 4). Experimental ewes represented a subset of a larger study assessing the impacts of divergent dietary zinc (Zn) concentrations [1× National Academics of Sciences, Engineering, and Medicine (NASEM) recommendations = CON or 3× NASEM recommendations = ZnTRT] throughout late gestation and lactation. Milk was collected at four periods during early lactation (18 – 24 h, 7 d, 14 d, and 21 d postpartum) and at weaning (84 ± 14 d postpartum). Somatic cell counts (SCC) were quantified, averaged, and classed (low: < 500 × 103; medium: 500 × 103 – 100 × 104; high: > 100 × 104 cells/mL). Milk samples (n = 67) were sequenced to identify bacteria and archaea; the most abundant phyla were Actinobacteria, Bacteroidetes, Cyanobacteria, Euryarchaeota, Firmicutes, Fusobacteria, Lentisphaerae, Proteobacteria, Spirochaetes, Tenericutes, Saccharibacteria TM7, and Verrucomicrobia. Mastitis pathogens were among the most relatively abundant genera, including Staphylococcus, Mannheimia, Corynebacterium, and Pseudomonas. Effects of breed, dietary Zn concentration, SCC class, and their two-way interactions on milk microbiome diversity and taxonomy were assessed within early (using a repeated measures model) and weaning samples. Alpha-diversity metrics included Pielou’s evenness, Faith’s phylogenetic diversity, and Shannon’s entropy indices. Main and interactive effects between Zn treatment, breed, SCC class, and period were variable in early lactation and not evident in weaning samples. Milk from BF ewes had increased Faith’s phylogenetic diversity and Shannon’s entropy, and differed in unweighted UniFrac composition (P = 0.10). Milk from CON ewes had a reduced rate of composition change through early lactation (P = 0.02) indicating greater microbiome stability than ZnTRT milk. These results support that milk is not sterile, and breed, dietary Zn concentration, and SCC class variably affect the milk microbiome. Findings from the current study provide important foundational insights into the effects of increased dietary Zn supplementation on longitudinal changes in the milk microbiome and associations with mammary gland health and mastitis.