Effects of Concentrate Supplementation on the Organic Matter Intake, Rumen Fermentation and Bacterial Community of Grazing Simmental Heifers

Abstract

Background: In grazing systems, supplementation is an effective way to improve ruminant performance. Little is known regarding how concentrate supplementation affects rumen fermentation and the bacterial community of grazing animals in the grasslands of northern China. Therefore, the objective of this study was to examine the effects of concentrate supplementation on the organic matter intake, rumen fermentation and bacterial community of grazing Simmental heifers. Twenty-four 7-month-old heifers were randomly divided into a supplement group and a control group (n = 12 per group). The control group heifers were grazed on a Leymus chinensis-based pasture without any supplementation (CON), while those in the supplement group (SUP) were grazed on the same grassland but received a concentrate supplement.Results: Compared with the CON heifers, those in the SUP group had a greater (P < 0.05) total organic matter (OM) intake and digestibility. However, heifers from the CON group had a higher (P < 0.05) herbage OM intake than those from the SUP group. The total VFA and NH3-N concentrations were significantly higher in the SUP group than in the CON group; of these, propionate, butyrate, and isobutyrate were also significantly increased in the SUP group. Furthermore, the acetate/propionate ratio was significantly decreased in the SUP group. Compared with the CON heifers, those in the SUP group had a higher bacterial richness. Firmicutes and Bacteroidetes were the two predominant bacteria at the phylum level, representing 54.32% and 38.59% of all sequences, respectively. Compared with the CON animals, the SUP animals showed significant (p < 0.05) increases in the relative abundance of Bacteroidetes and Verrucomicrobia, but supplementation did not affect the relative abundance of other bacteria at the phylum level. At the genus level, different diet treatments had an important effect on the relative abundance of the major genera (Fig. 3C). The relative abundance of the genus Butyrivibrio was greater (p < 0.05) in the SUP group than in the CON group. The relative abundances of the genera Rikenellaceae_RC9_gut_group, Ruminococcaceae_UCG-010 and Ruminococcaceae_UCG-011 were higher (p < 0.05) in the CON group than in the SUP group.Conclusions: In conclusion, providing 1.28 kg of supplement (DM basis) is a nutritional management strategy that can be adopted to improve the rumen fermentation, organic matter intake and digestibility of grazing heifers. Furthermore, supplementation has significant effects on the microbial community in the rumen of heifers, which might contribute to the anatomic development of the rumen, and these findings will contribute to the direction of future research in grazing heifers.