Table 1. Summary of the studies used for the meta-analysis

Study no. References Animals NOP level (mg/kg DMI) Methods of administration Forage ratio (in TMR, %) NDF(%DM) CH4 measurement
1 Martínez-Fernández et al. [9] Sheep 0 and 111.2 Direct administration via cannula 54.4 41.5 RCS
2 Romero-Perez et al. [15] Beef 0, 47.4, 143.6, and 304.9 Top dressed 60.0 37.6 RCS
3 Romero-Perez et al. [16] Beef 0 and 280.1 Mixed with diet 60.0 38.6 RCS
4 Vyas et al. [13] Beef 0, 100, and 200 Mixed with diet 8 and 70.0 19.2 and 36.4 RCS
5 Vyas et al. [14] Beef 0, 50, 75, 100, 150, and 200 Mixed with diet 8.0 and 65.0 27.0 and 41.7 RCS
6 Vyas et al. [12] Beef 0, 125 and 200 Mixed with diet 8.0 and 65.0 18.4 and 40.5 RCS
7 Martinez-Fernandez et al. [11] Beef 0 and 337.8 Mixed with roughage 100.0 66.1 RCS
8 Kim et al. [10] Beef 0 and 100 Mixed with diet and direct administration via cannula 9.8 and 64.4 14.6 and 28.3 GFS
9 Haisan et al. [17] Dairy 0 and 129.5 Mixed with diet 37.9 26.5 SF6
10 Reynolds et al. [21] Dairy 0, 26.6 and 135.1 Direct administration via cannula 51.2 39.8 RCS
11 Hristov et al. [19] Dairy 0, 40.0, 60.0, and 80.0 Mixed with diet 60.7 27.6 GFS and SF6
12 Lopes et al. [20] Dairy 0 and 60.0 Mixed with diet 55.5 30.9 GFS
13 Haisan et al. [18] Dairy 0, 68.3 and 132.3 Mixed with diet 60.0 33.8 SF6
14 Van Wesemael et al. [22] Dairy 0, 71.7 and 75.1 Mixed with roughage and mixed in pellet 65.8 34.6 GFS
NOP, 3-nitrooxypropanol; DMI, dry matter intake; TMR, total mixed ration; NDF, neutral detergent fiber; CH4, methane; RCS, respiratory chamber system; SF6, sulfur hexafluoride tracer; GFS, GreenFeed System; VFA, volatile fatty acids; MP, microbial population; MC, milk component.