Environmental Impacts from Cattle Consuming Tannin-Containing Hays

The cow-calf phase accounts for approximately 80% of total greenhouse gas emmissions attributed to beef production systems. There is potential for tannin-containing hays to reduce these environmental impacts. Fifteen mature beef brood cows and 9 yearling beef heifers were blocked by weight and randomly assigned to 3 groups of 5 cows or 3 heifers and fed tannin-containing (birdsfoot trefoil-BFT, sainfoin-SAN, small burnet-SML), or non-tannin containing (alfalfa-ALF, cicer milkvetch-CMV, meadow bromegrass-MB) hays in 4 trials. Groups of cows were fed BFT, CMV or MB in Trial 1 and ALF, SAN or SML in Trial 3. Groups of heifers were fed ALF, MB or SAN in Trial 2 and BFT, CMV or SML in Trial 4. Each trial used a completely randomized block design with repeated measures during 5 days following a 14-d adjustment period. Nine cows and 9 heifers were selected for total collection of enteric methane using the SF6 methodology, feces and urine while intake was measured for all animals. Methane emission from cows was lower for SML than ALF (P=0.04) or SAN (P=0.03; Table 1). Additionally, cows and heifers fed tannin-containing hays had lower urine urea nitrogen (UUN) and blood urea nitrogen (BUN) than animals fed non-tannin containing hays (Table 1), suggesting a shift in nitrogen excretion from urine to feces. In conclusion, tannin-containing legumes consumed as hays have the potential to reduce environmental impacts attributed to cattle fed in confinement.

Table 1.

Treatments (Cows)
Trial	Trial 1					Trial 3
Items	BFT	CMV	MB	SEM	P-Value	ALF	SAN	SML	SEM	P-Value
BUN (mg/dL)	6.9a	16.5b	10.0a	1.6	0.0033	18.7a	13.4b	4.2c	1.8	0.0003
UUN (g/day)	81.7ac	228.7b	82.9c	19.9	0.0043	216.8	98.6a	24.4b	26.6	0.0084
CH4 (L/day)	46.29a	44.84a	55.12a	5.97	0.51	52.79a	51.37a	28.72b	5.79	0.048
Intake (g intake/kg BW)	15.5a	15.19a	12.27a	1.94	0.45	15.92ab	12.82a	18.29b	1.44	0.062
Treatments (Heifers)
Trial	Trial 2					Trial 4
Items	ALF	MB	SAN	SEM	P-Value	BFT	CMV	SML	SEM	P-Value
BUN (mg/dL)	27.9a	10.9b	14.9b	16.1	0.0007	14.8a	19.2a	4.5b	27.7	0.023
UUN (mg/day)	238.7a	32.8b	44.1b	17.5	0.0003	119.6a	183.9b	23.8c	8.2	<.0001
CH4 (L/day)	54.11a	52.58a	37.09a	7.57	0.26	37.25a	39.08a	36.11a	5.15	0.91
Intake (g intake/kg BW)	24.42a	16.95b	19.86ab	0.95	0.0043	23.0a	19.78b	16.96c	0.68	0.0021

Means in a row with different superscripts differ (p<0.1).