Effect of different seasons (spring vs summer) on the microbiota diversity in the feces of dairy cows.

We aimed to study how seasonal heat stress (i.e., spring vs. summer) influenced microbiota diversity in the dairy cows' feces using Illumina MiSeq sequencing. Sixteen dairy cows were experiencing spring thermoneutral conditions (daily mean temperature = 18.8 ± 3.40 °; daily mean THI = 64.29 ± 4.94) and 16 under summer heat stress (daily mean temperature = 27.63 ± 5.34 °; daily mean THI = 82.56 ± 1.74). Fecal samples were collected per cow three times daily from day 18 to day 22 during each experimental period. Results revealed that the microbiota diversity in the feces was significantly lower (P < 0.05) under summer heat stress. At both the phylum and genera levels, significant differences were observed on microbiota composition in cow's feces between spring and summer. The most dominant phylum was Firmicutes, contributing 69.45% and 87.14% of the fecal microbiota in spring and summer, respectively, followed by Bacteroidetes, contributing 25.27% and 4.45%, respectively. Compared with the dairy cows in the spring season, the relative abundance of unclassified Peptostreptococcaceae, Turicibacter, and Clostridium_sensu_stricto_1 (P < 0.05) were greatly increased (P < 0.05), while the significant decrease in the proportion of Ruminococcaceae_UCG-005 and Rikenellaceae_RC9_gut_group as well as Bacteroides were observed in hot summer. Prediction of microbiota gene function in feces based on PICRUSt method found that different microbiota between spring and summer were mainly concentrated on the function related to membrane transport, infectious diseases, immune system diseases, and lipid metabolism. This study demonstrates that diversity and composition of fecal microbiota in dairy cows varies under different THI condition, and the relationship between fecal microbiota and cows' health needs further research.