Abstract
Limit-feeding of a high concentrate diet has been proposed as an effective method for improving feed efficiency and reducing total manure output of dairy heifers; meanwhile the effects of this method on hindgut microbiota are still unclear. This study investigated the effects of a wide range of dietary forage:concentrate ratios (F:C) on the fecal composition of bacteria and archaea in heifers using next-generation sequencing. Four diets with different F:C (80:20, 60:40, 40:60, and 20:80) were limit-fed to 24 Holstein heifers, and the fecal fermentation parameters and bacterial and archaeal communities were investigated. With increasing dietary concentrate levels, the fecal dry matter output, neutral detergent fiber (NDF) content, and proportion of acetate decreased linearly (P < 0.01), while the fecal starch content and proportions of propionate, butyrate, and total branched-chain volatile fatty acids (TBCVFAs) were increased (P ≤ 0.05). An increased concentrate level linearly increased (P = 0.02) the relative abundance of Proteobacteria, and linearly decreased (P = 0.02) the relative abundance of Bacteroidetes in feces. At the genus level, the relative abundance of unclassified Ruminococcaceae and Paludibacter which may have the potential to degrade forage decreased linearly (q ≤ 0.02) with increasing dietary concentrate levels, while the relative abundance of Roseburia and Succinivibrio which may be non-fibrous carbohydrate degrading bacteria increased linearly (q ≤ 0.05). Some core microbiota operational taxonomic units (OTUs) also showed significant association with fecal VFAs, NDF, and/or acid detergent fiber (ADF) content. Meanwhile, the relative abundance of most detected taxa in archaea were similar across different F:C, and only Methanosphaera showed a linear decrease (P = 0.01) in high concentrate diets. Our study provides a better understanding of fecal fermentation parameters and microbiota under a wide range of dietary F:C. These findings support the potential for microbial manipulation by diet, which could enhance feed digestibility and relieve environmental problems associated with heifer rearing.
Highlights
Ruminants are uniquely able to convert large quantities of plant fiber into high quality products, such as meat and milk, for human consumption
After operational taxonomic units (OTUs) picking and chimera checking, a total of 1,091 OTUs were calculated for all the samples at 3% dissimilarity
Because a limit-feeding strategy was used in our study, the total VFA (TVFA) concentrations were a little lower than that in previous reports (Li et al, 2012; Mao et al, 2012, 2015)
Summary
Ruminants are uniquely able to convert large quantities of plant fiber into high quality products, such as meat and milk, for human consumption. With the current rapidly exploding human population, there is a great need to increase ruminant productivity and feed conversion efficiency (Thornton, 2010). The limit-feeding of high concentrate diets has been proposed as an effective method for improving feed efficiency in heifers, and has been explored by many researchers (SuarezMena et al, 2015; Lascano et al, 2016; Zanton and Heinrichs, 2016). When heifers are raised under a limit-fed diet of enhanced energy density, intakes of feed and forage are reduced, as is fecal or total manure output (Moody et al, 2007; Zanton and Heinrichs, 2009); this is an environmentally friendly dairy farming strategy. The effects of limit-feeding different forage to concentrate ratios (F:C) on hindgut microbiota communities are still unclear
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