Effects of Grazing Diverse Combinations of Sainfoin, Birdsfoot Trefoil and Alfalfa on Beef Cow Performance and Environmental Impacts

Diverse combinations of forages with different nutrient profiles and plant secondary compounds may improve the efficiency of nutrient utilization by livestock. We tested the effects of grazing increasingly diverse combinations of the tannin-containing legumes sainfoin (SAIN) and birdsfoot trefoil (BFT) and the saponin-containing legume alfalfa (ALF) on cattle performance, digestible dry matter (DDM), blood urea nitrogen (BUN) and methane emissions. Twenty-one pairs of heifers grazed three replications of seven treatments (single species, choice of all possible 2-way combinations, or a 3-way choice) in a completely randomized block design. Animals grazed during 2 periods of 28-d each and composited forage and fecal samples were collected during five consecutive days at the end of each period to estimate apparent digestibility, using acid detergent lignin as an internal marker. Methane emissions from ALF and SAIN were assessed using the sulfur hexafluoride technique during each 5-d collection period. Data were analyzed as a repeated measures design with cows (random effect) nested within treatments, and period and day as the repeated measures. Average daily gain for the 3-way choice was 26% and 30% greater than for the 2-way choices and monocultures, respectively (P<0.05). Gains of animals grazing tannin-containing legumes were 34% (BFT) and 17% (SAIN) greater than for those grazing ALF (Table 1). Methane emissions per unit of gain were greater for ALF than for SAIN and DDM peaked for the ALF-SAIN combination and for the 3-way choice. Cattle grazing tannin-containing legumes as monocultures or in combinations showed lower BUN values than animals under ALF monocultures or legume combinations that had ALF, suggesting a shift in the site of N excretion from urine to feces. In conclusion, diverse combinations of legumes have the potential to enhance livestock performance over less diverse arrays of forages. Tannin-containing legumes in monocultures or in combinations may contribute to reducing methane emissions and urinary nitrogen excretion in grazing cattle.

Table1.

Treatments
Item	ALF	SAIN	BFT	ALF-SAIN	ALF-BFT	SAIN-BFT	ALF-SAIN-BFT	SEM	P-Value
DM,%	26.1a	26.7a	22.3b					0.63	0.002
CP,%	26.8a	21.9c	24.0b					0.37	0.002
ADF,%	17.6b	19.8a	16.3c					0.63	0.010
ADG,kg/d	0.82c	0.96bc	1.10ab	0.97bc	0.85c	1.16ab	1.25a	0.09	0.022
DDM,%	71.8cd	74.7abc	72.4bcd	76.1a	71.0d	70.3d	75.6ab	1.49	0.051
BUN,mg/dL	19.5a	12.0d	13.8cd	16.2bc	17.8ab	14.5cd	16.7abc	1.24	0.013
Methane,g/kg ADG	336.6a	253.7b						36.56	0.097

Different superscript letters differ (P<0.1).