Repeated inoculation of cattle rumen with bison rumen contents alters the rumen microbiome and improves nitrogen digestibility in cattle

Abstract

Future growth in demand for meat and milk, and the socioeconomic and environmental challenges that farmers face, represent a "grand challenge for humanity". Improving the digestibility of crop residues such as straw could enhance the sustainability of ruminant production systems. Here, we investigated if transfer of rumen contents from bison to cattle could alter the rumen microbiome and enhance total tract digestibility of a barley straw-based diet. Beef heifers were adapted to the diet for 28 days prior to the experiment. After 46 days, ~70 percent of rumen contents were removed from each heifer and replaced with mixed rumen contents collected immediately after slaughter from 32 bison. This procedure was repeated 14 days later. Intake, chewing activity, total tract digestibility, ruminal passage rate, ruminal fermentation, and the bacterial and protozoal communities were examined before the first and after the second transfer. Overall, inoculation with bison rumen contents successfully altered the cattle rumen microbiome and metabolism, and increased protein digestibility and nitrogen retention, but did not alter fiber digestibility.

Figure 1

Mean daily ruminal pH of heifers fed a barley straw diet before and after rumen content transfers from the bison (5 days of measurement). No treatment or treatment × time interaction (P > 0.05) was observed.

Figure 2

Principal coordinate analysis (PCoA) of ruminal bacterial OTUs from cattle before rumen content transfers and after transfers (days 1 and 27), and from the second bison inoculum used in the transfers. Proportion of variance explained by each principal coordinate axis is denoted in the corresponding axis label.

Figure 3

Experimental layout. The 16 heifer were divided in 2 groups of 8 animals of similar average body weight (G1 and G2) for the fractional rate of passage study. These 2 groups were further sub-dived in 4 groups of 4 heifers each with similar average body weight (G1A, G1B, G2A and G2B) for the other measurements. Rumen sampling for Bacterial composition were conducted in all the heifers in the same days.