292 Characterizing methane emissions through In vivo and ex vivo models during a transition from a high-forage to a high-grain diet.

Abstract Most studies measuring methane (CH4) emissions from beef cattle have identified a transition period during which animals adapt from a high-forage to a high-grain diet. During this transition, methane production progressively decreases and eventually stabilizes. However, the precise duration of this transition period is not well-defined and remains unclear. On this study, methane production was measured daily using in vivo and weekly using an ex vivo model. The objectives of this study were to determine the number of days required for rumen methane production to stabilize during the transition from a high-forage to a high-grain diet, and to assess the correlation between both measurement methods. Fourteen Angus crossbred steers (294 ± 30.8 kg) were used in a generalized randomized block design. Steers were housed in one pen, equipped with four Vytelle Sense feed bunks (Vytelle LLC, Lenexa, KS) and a Greenfeed unit (C-Lock Inc., Rapid City, SD), with ad-libitum access to feed and water. The experimental period included 2-wk of adaptation to the Greenfeed system, followed by 11 wk of dietary changes. The steers were initially fed a 100% forage-based diet for 14 d. From d 14 to d 28 the diet was gradually shifted until reaching a high-grain formulation on d 28, and it was kept to the end of the study. Daily methane emissions were recorded throughout the experiment to monitor changes in methane production due to diets. Individual feed intake was recorded daily, and body weight was recorded weekly. In addition. weekly rumen fluid samples were collected to assess ruminal fermentation parameters including pH, total gas and CH4 production using the ex vivo model (24-h and 48-h incubations). During the transition from a high-forage to a high-concentrate diet, CH4 emission yield decreased by 58% (from 17.1 to 7.1 g of CH4/kg of dry matter consumed). Methane yield appears to stabilize by week 3 after the initiation of the transition but then increased slightly on weeks 4 and 5 after the transition. Methane yield appears to stabilize completely after 6 weeks following a high-forage diet, and remains constant (averaging 7.8 g of CH4/kg of dry matter consumed). Based on these results, it appears that a minimum of 6 weeks is needed to definitely stabilize enteric methane yield in beef steers transitioning from a high-forage to a high-grain diet.