Longitudinal Changes of the Ruminal Microbiota in Angus Beef Steers

Abstract

The ruminal microbiota of Angus cows and steers were characterized using 16s rRNA gene sequencing, and the expression of their metabolic pathways was predicted. Samples were collected on weaning day from the steers and the cows, and subsequently on three other occasions from the steers. Results showed that microbial richness, evenness, and diversity decreased (p < 0.001) in the rumen of the steers as they were weaned and transitioned to a high-concentrate feedlot diet. However, on the day of weaning, microbial evenness was similar to that observed in the rumen of cows (p = 0.12). The abundance of archaea was similar (p = 0.59) between the cows and steers at weaning, but it decreased (p = 0.04) in the rumen of steers after weaning, and remained stable (p ≥ 0.44) for the remainder of their lives. Likewise, no difference (p = 0.51) in the abundance of Bacteroidetes was detected between the cows and the calves on the day they were weaned, but the abundance of this phylum increased (p = 0.001) and remained stable after that. These results suggest that cows may have a strong influence on the composition, and help modulate the ruminal microbiota of young calves; however, following weaning, their ruminal microbiotas tend to differentiate from that state observed at earlier ages.

Keywords: calf; cow; dam; metabolic pathway; microbiome; rumen development.

Figure 1

Principal coordinates analysis of Beta-diversity (Unweighted UniFrac) observed in the ruminal samples of the adult cows, steers on weaning day, steers at beginning of feedlot phase (on-test), steers at end of feedlot phase (off-test), and upon arriving at the slaughterhouse (lairage). PERMANOVA p-value = 0.001.

Figure 2

Number of observed features and Pielou’s evenness index observed in the ruminal samples of the adult cows, steers on weaning day, steers at beginning of feedlot phase (on-test), steers at end of feedlot phase (off-test), and upon arriving at the slaughterhouse (lairage). Average values and significance for the contrasts are presented in Table 1.

Figure 3

Shannon diversity index and Faith’s phylogenetic diversity index observed in the ruminal samples of the adult cows, steers on weaning day, steers at beginning of feedlot phase (on-test), steers at end of feedlot phase (off-test), and upon arriving at the slaughterhouse (lairage). Average values and significance for the contrasts are presented in Table 1.

Figure 4

Percentage of archaea detected in the ruminal samples of the adult cows, steers on weaning day, steers at beginning of feedlot phase (on-test), steers at end of feedlot phase (off-test), and upon arriving at the slaughterhouse (lairage). A significant difference (*) was detected between steers at weaning and at beginning of the feedlot phase (p = 0.04); but not for the other contrasts (p ≥ 0.44).

Figure 5

The abundance of the main phyla in the ruminal samples of the adult cows, steers on weaning day, steers at beginning of feedlot phase (on-test), steers at end of feedlot phase (off-test), and upon arriving at the slaughterhouse (lairage).