Abstract/Summary

Ruminant agricultural systems are under pressure to reduce methane (CH4) emissions and increase carbon sequestration. Condensed tannins can bind proteins, reducing ruminal degradation (and subsequent N outputs) and methanogenesis. Willow fodder contains condensed tannins, therefore, willow silvopastoral systems have potential for reduced CH4 and nitrous oxide emissions and increased soil carbon sequestration. The objective is to explore if growing beef cattle would graze Willow fodder and to quantify the effect on performance and CH4 production. Twenty growing beef steers were blocked into 2 subgroups (2 × 10) and used in a 2 (treatment) × 2 (period) Latin square design study. The two grazing strategy treatments were Perennial Ryegrass (Control) vs Willow fodder mix with a grass understory. Condensed tannins in Willow was 48 g/kg DM. Daily liveweight (LW) of each animal was recorded by a Beef Monitor Unit: an automatic weigh system (Ritchie, Scotland, UK). Methane, hydrogen (H2), and carbon dioxide (CO2) production and oxygen (O2) consumption from all animals were measured during the last two weeks of each period using two GreenFeed units (C-LOCK, South Dakota, USA). Pellets were offered as bait at 40 g/drop which ensured the cattle were in the unit for 3–5 minutes at each time and allowed access of maximum 5 measurement periods/day. Gaseous exchange data were used to calculate heat production (HP), and then ME intake (HP plus energy retention estimated from liveweight gain (LWG)) and GE intake (GEI). The average LW of the cattle by Grass and Willow treatment were 507 kg and 513 kg respectively. LWG (kg/d) differed (P < 0.01) by treatment (Grass: 1.04; Willow: 0.72), however, the effect was derived from P2 (LWG for grass vs willow in P1 = 0.76 vs 0.75 kg/d and in P2 = 1.29 vs 0.69 kg/d). HP (MJ/d) did not differ between treatment (Grass: 82.4; Willow: 84.3) as well as ME intake (MJ/d) (Grass: 110; Willow: 102). CH4 (g/d) production reduced by 27% for the Willow treatment (P < 0.001 ; 236.7 vs 173.5). While CH4/LW (g/kg) reduced by Willow treatment (P < 0.001), CH4/LWG (g/kg) showed no differences between Grass and Willow treatments (0.27 vs 0.30, P = 0.555). CH4-E/GEI reduced by 22% on the Willow vs Grass treatments (6.0 vs 7.70%). H2, CO2 and O2 production (g/d) showed no significant differences between treatments. Willow Silvopastoral systems could be a grazeable forage for cattle with potential to reduce CH4 production. Further in vivo animal trials are needed to quantify the effect of grazing willow fodder on protein metabolism. Acknowledgements: We thank Brook Hall Estate in N.Ireland and Prof. John Gilliland for providing the Willow grazing platform and Food Foyle Food Group for the animals. Funded by DAERA and UKRI-BBSRC.