Improving Grazing Capacity Through Introduction of Bloat Free Legumes in Existing Pasture Stands

Three experiments were conducted over 5 yr to evaluate the inclusion of bloat-free legumes through sod-seeding in existing pasture stands, with respect to plant persistence under grazing pressure, animal performance, rumen fermentation, enteric methane production and economic impact. Experiment 1 was separated into two parts, the first which assessed 2 legumes (CMV; cicer milkvetch [Astragalus cicer L] and sainfoin [SAIN; Onobrychis viciifolia Scop.]) at 2 stages (vegetative and late flower) incubated with alfalfa (ALF; Medicago sativa) at 5 inclusion rates 0:100; 25:75, 50:50, 75:25 and 100:0 (as DM) incubated in batch culture. The second part of experiment 1 assessed CMV and ALF at the vegetative physiological stage (16-30 cm stem length, no buds, flowers or seed pods) were incubated in ratios of 25:75, 50:50, 75:25 and 100:0 (as DM) in RUSITEC. In batch culture, dry matter disappearance (DMD) increased linearly (P ≤ 0.01), propionate concentration (mol 100mol-1) increased linearly (P = 0.02), and methane (mg g-1 DMD) decreased linearly (P ≤ 0.01) with vegetative CMV inclusion. In RUSITEC, DMD, ADF and NDF digestibility were increased quadratically (P ≤ 0.01) with increased vegetative CMV inclusion. Total ruminal SCFA production (mmol d-1) did not change (P=0.59); however, acetate to propionate ratio and NH3-N (mmol d-1) were linearly decreased (P<0.01), and total microbial protein synthesis and efficiency of microbial protein synthesis were linearly increased (P<0.05) with increased vegetative CMV inclusion. In experiment 2, a two-year (2017, 2018) replicated (n=6) experiment was conducted to evaluate the effect of bloat-free legumes on grazing animal ruminal fermentation, ruminal microbial populations, and enteric methane production. Each yr, 15 ruminally cannulated cows (average 739 kg ± 40kg) were randomly allocated to 1 of 3 replicated (n=6) treatments: grazing sod-seeded SAIN; grazing sod-seeded CMV; or grazing non-sod-seeded control (CONT). Total short chain fatty acid production (mmol d-1; P = 0.59) and acetate (mol 100mol-1; P = 0.26) did not differ between treatments. Propionate increased linearly (P ≤ 0.01) and butyrate decreased linearly (P ≤ 0.01) with increased CMV inclusion. Acetate to propionate ratio decreased linearly (P=0.01) in cattle grazing CMV paddocks compared CONT or SAIN. Ruminal ammonia (NH3-N) concentration and plasma urea nitrogen were linearly increased (P ≤ 0.01) in cattle grazing CMV paddocks compared to SAIN and CONT. Enteric methane (g kg-1 DMI) and ruminal microbial populations were not impacted by treatment. In experiment 3, a five-year experiment evaluated the effects of sod-seeding SAIN and CMV into mixed alfalfa-meadow bromegrass (Lanigan, SK) (CONT) or monoculture alfalfa (Lethbridge, AB) (CONT) stands on pasture productivity, steer performance, and economics. At Lanigan, SAIN decreased (treatment × year, P = 0.01) from 13% in yr 1 to 2% in yr 2 (% plant population) and did not differ thereafter, while CMV, maintained a proportion of 16% in the stand. Forage yield was greater (treatment × year; P < 0.01) in yr 1 in the SAIN and CMV milkvetch treatments compared to CONT. Dry matter intake (DMI) of steers was greater only in yr 5 and ADG was greater (P < 0.01) in SAIN and CMV treatments compared to CONT. At Lethbridge, SAIN decreased (treatment × year; P = 0.01) from 46 to 17% (% DM yield), while CMV maintained its proportion at 11% over 5 yr. Forage yield increased (treatment × year; P < 0.01) only in yr 2 and 3 of SAIN, compared to CMV or CONT. Average daily gain (kg d-1) was not affected by treatment (treatment × year; P = 0.12). At Lanigan, SAIN and CMV generated greater gross returns compared to control; however, once establishment costs were applied there were no differences in present value of net returns. \nThroughout the three experiments outlined in this thesis, the data suggests possible increases in energetic efficiency and microbial protein synthesis may be observed in cattle grazing mixed CMV pasture compared to ALF when grazed at equal maturity. Results also suggests CMV may be more persistent in mixed pasture under variable environmental conditions, when compared to SAIN; however, risk associated with increased undesirable species in sod-seeded paddocks were observed and cannot be overlooked. Costs associated with sod-seeding CMV and SAIN, such as fertilizer and seed price, combined with variable forage yield and animal performance, reduced the economic feasibility of sod-seeding these species which may limit producer uptake of this type of pasture rejuvenation. The results of these experiments highlight the dynamic environment of mixed species pastures, as results varied depending on level of legume inclusion in pasture, species sod-seeded, and existing pasture species. More research is required to determine the agronomic best management practices for pasture rejuvenation, the impact of pre-existing pasture species on newly introduced species, and the impact of non-tanniferous legumes, such as CMV, on livestock production.

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