In vitro Fermentation Profile and Methane Production of Kikuyu Grass Harvested at Different Sward Heights

Guillermo Correa,Ángel S. Zubieta,Paulo César de Faccio Carvalho,Alejandra Marín,Jérôme Bindelle,Jacobo Arango,Ngonidzashe Chirinda

doi:10.3389/fsufs.2021.682653

Abstract

Highly digestible forages are associated with anin vitrolow-methane (CH4) rumen fermentation profile and thus the possibility of reducing CH4emissions from forage-based systems. We aimed to assess thein vitroruminal fermentation profile, including CH4production, of the top stratum of Kikuyu grass (Cenchrus clandestinus - Hochst. ex Chiov) harvested at different sward heights (10, 15, 20, 25, and 30 cm). Herbage samples (incubating substrate) were analyzed for their chemical composition,in vitroorganic matter digestibility (IVOMD), and morphological components.In vitroincubations were performed under a randomized complete block design with four independent runs of each treatment. Gas production (GP),in vitrodry matter digestibility (IVDMD), CH4production, total volatile fatty acid (VFA) concentration, and their acetate, propionate, and butyrate proportions were measured following 24 and 48 h of incubation. Herbage samples had similar contents of organic matter, neutral detergent fiber, and crude protein for all treatments. However, a higher acid detergent fiber (ADF) content in taller sward heights than in smaller sward heights and a tendency for metabolizable energy (ME) and IVOMD to decrease as sward height increased were found. Similarly, the stem + sheath mass tended to increase with increasing sward height. Amongst the nutrients, ME (r= −0.65) and IVDMD (r= −0.64) were negatively correlated with sward height (p&lt; 0.001) and ADF was positively correlated with sward height (r= 0.73,p&lt; 0.001). Both the GP and IVDMD were negatively related to the sward height at both incubation times. Sward heights of Kikuyu grass below 30 cm display anin vitroprofile of VFAs high in propionate and low in acetate, with a trend toward lower methane production of CH4per unit of IVDMD. These findings are important to aid decision-making on the optimal sward height of Kikuyu grass and manage animal grazing with the opportunity to reduce CH4production.

Highlights

Livestock is under fire of critics for its major share in the environmental impact of the agricultural sector
No differences were found for OM, neutral detergent fiber (NDF), and CP contents (p > 0.05, Table 2), the acid detergent fiber (ADF) concentration was greater at 30 cm sward heights than at 10 cm sward heights, but not different from other sward heights (p = 0.02, Table 2)
The in vitro organic matter digestibility (IVOMD) and metabolizable energy (ME) tended to decrease with increasing sward height (p = 0.16 and p = 0.10, respectively; Table 2)

Summary

Introduction

Livestock is under fire of critics for its major share in the environmental impact of the agricultural sector. Total global greenhouse gas (GHG) emissions from livestock (animals, manure, feed production, and land-use change) are estimated to account for 14.5% of total anthropogenic emissions (Gerber et al, 2013). Ruminants produce methane (CH4) as a natural byproduct of microbial fermentation of feed in the rumen, contributing approximately 6% of the global anthropogenic GHG emissions (40% of all livestock emissions; Gerber et al, 2013; Beauchemin et al, 2020). Current grazing systems are being redesigned to link animal production with environmental management (Boval and Dixon, 2012; Carvalho, 2013) in light of current demands for sustainable agricultural production around the world (Herrero et al, 2010; Mottet et al, 2017)

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