Increased Nitrogen Retention and Reduced Methane Emissions of Beef Cattle Grazing Legume vs. Grass Irrigated Pastures in the Mountain West USA

Abstract

Grazing studies were carried out over a 5-year period using pregnant cows, yearling calves and 2-year-old heifers to investigate the influence of diet on intake, methane (CH4) emissions and retention of nitrogen (N). Monoculture legume (birdsfoot trefoil, BFT and cicer milkvetch, CMV) or grass (meadow bromegrass, MBG) pastures were rotationally stocked, and during year 4 and year 5, treatments were contrasted with total mixed rations (TMR) fed in confinement. The sulfur hexafluoride (SF6) method was used to continuously measure enteric CH4 emissions. Intake was greater on legume pastures and on TMR than on grass pastures, and enteric CH4 emissions per unit of intake were lower on legumes compared with grass pastures. Legume pastures had elevated non-fiber carbohydrate (NFC) concentrations (400 g kg−1 dry matter; DM) typical of perennial legumes cultivated in the Mountain West. A N balance calculated in 2017–2018 demonstrated that N retention was greater for TMR and legume than grass pastures. Enteric CH4 emissions of grazing cow herds account for the majority of greenhouse gas (GHG) emissions from beef production and can be significantly reduced by using highly digestible forage legumes. The N retention of legumes can potentially enhance the efficiency of N use, thereby increasing the sustainability of grasslands.

Potential benefits of tanniferous forages in integrative crop-livestock agroecosystems

“…MacAdam et al (2022) showed that legumes had greater crude protein, in vitro true dry matter digestibility, and non-fiber carbohydrates than the grass, while grass had greater neutral detergent fiber, acid detergent fiber, and crude fiber than legumes. Digestibility was found to be greater for the legumes than for the grass as well, and the total digestible nutrients of legumes was always greater than the grass and exceeded that of the high-forage confinement total mixed rations also tested in that study Ruminants consuming a higher quality diet due to the enhanced protein content and digestibility of legumes utilized as cover crops, grazed, or inter-seeded into grains, compared with grazing crop residues and/or grazing grasses, have increased productivity and reduced effect of environmental wastes such as methane or ammonia (MacAdam, et al, 2022). Better quality diets also reduce the CH 4 output per unit of product and therefore a target quantity of animal product can be achieved at lower CH 4 emissions and with fewer animals, improving both the productivity and sustainability of the agroecosystem.…”

“…These same benefits have been observed when tanniferous legume hay and silage has been fed (Christensen et al, 2015;Broderick et al, 2017) though with reduced effect compared with fresh forages. Regardless of the state of the forages (fresh or dried), the integrative system that utilizes tanniferous forages improves diet quality as legumes are generally digested more quickly and to a greater extent than grasses, as documented is a multi-year study (MacAdam et al, 2022). MacAdam et al (2022) showed that legumes had greater crude protein, in vitro true dry matter digestibility, and non-fiber carbohydrates than the grass, while grass had greater neutral detergent fiber, acid detergent fiber, and crude fiber than legumes.…”

“…Regardless of the state of the forages (fresh or dried), the integrative system that utilizes tanniferous forages improves diet quality as legumes are generally digested more quickly and to a greater extent than grasses, as documented is a multi-year study (MacAdam et al, 2022). MacAdam et al (2022) showed that legumes had greater crude protein, in vitro true dry matter digestibility, and non-fiber carbohydrates than the grass, while grass had greater neutral detergent fiber, acid detergent fiber, and crude fiber than legumes. Digestibility was found to be greater for the legumes than for the grass as well, and the total digestible nutrients of legumes was always greater than the grass and exceeded that of the high-forage confinement total mixed rations also tested in that study Ruminants consuming a higher quality diet due to the enhanced protein content and digestibility of legumes utilized as cover crops, grazed, or inter-seeded into grains, compared with grazing crop residues and/or grazing grasses, have increased productivity and reduced effect of environmental wastes such as methane or ammonia (MacAdam, et al, 2022).…”

Beef Steer Performance on Irrigated Monoculture Legume Pastures Compared with Grass- and Concentrate-Fed Steers

“…In 2013, the remaining 10 steers were assigned to the grass treatment and continuously grazed a single endophyte-free tall fescue pasture for the first 3 weeks of the grazing period because MBG pastures were newly established; cattle were moved to MBG pastures for the remaining 9 weeks of the study. Pairs of steers with similar total BW were randomly assigned to one of five MBG pasture replications [3]. Each replication was subdivided into 12 paddocks, and pairs of steers were moved to a fresh paddock every 3.5 days within the replication.…”

“…Most ruminant production occurs on grasslands [1], and compared with grass-based production, legume-based production can provide advantages, including biologically fixed nitrogen and the increased digestibility and intake [2] that result in reduced methane emissions as a function of intake [3]. The presence of condensed tannins, which are secondary metabolites, makes temperate legumes non-bloating, decreases protein degradation in the rumen, reduces the nitrogen concentration of urine by partitioning more nitrogen into feces, and may function as an anthelmintic [4].…”