Enteric methane, manure composition, and anaerobic digestor methane potential in lactating cows fed diets differing in substitution of dried distillers grains and solubles

Abstract

Two experiments were conducted to evaluate enteric methane, manure composition, and digestor methane potential in lactating cows fed diets differing in substitution of dried distillers grains and solubles (DDGS). The objectives of experiment 1 were to examine the effects of feeding DDGS by reducing dietary starch, NDF, and forage NDF (fNDF) on enteric methane production, feed intake, energy and N utilization, manure output, and milk production in lactating Jersey cows. Twelve multiparous Jersey cows (98 ± 6.5 DIM and weighing 441 ± 26.9 kg) were arranged in a triplicated 4 × 4 Latin square design consisting of 4 periods of 28 d. Cows were randomly assigned to 1 of 4 treatment diets: control (CON; 0% DDGS); reduced fiber (RF; based upon 13% DDGS and lower in NDF and fNDF than CON); reduced starch (RS; based upon 13% DDGS and lower in starch than CON); and intermediate (INT; 6.5% DDGS but compared with RF and RS, intermediate in fiber and starch). Diets were balanced to be isonitrogenous (16.6% ± 0.15% CP). Diet amylase-treated NDF on an OM basis (aNDFom) was 28.6%, 26.9%, 31.9%, and 29.2% and starch was 28.2%, 29.7%, 22.8%, and 27.2% DM for CON, RF, RS, and INT, respectively. Compared with CON, DMI increased when cows consumed RF (18.2 vs. 19.4 ± 0.60 kg/d for CON and RF, respectively), but intake for cows consuming RS or INT (average 18.6 ± 0.60 kg/d) did not differ compared with CON. Energy-corrected milk yield increased with RF (37.4 vs. 39.7 ± 1.07 kg/d for CON and RF, respectively), but RS or INT (average 37.5 ± 1.07 kg/d) did not differ from CON. No differences were observed for the ratio of ECM to DMI (average 2.04 ± 0.045 kg/d). Treatments did not affect methane production (average 413.2 ± 20.85 L/d). Compared with CON, manure output (sum of feces and urine output) increased when cows consumed RS (59.1 vs. 63.2 ± 1.89 kg/d for CON and RS, respectively), but no difference was seen for RF or INT (average 60.2 ± 1.89 kg/d). Manure volatile solids (VS) output increased when feeding RF (5.35 vs. 5.70 ± 0.169 kg/d for CON and RF, respectively), but no difference was seen when feeding RS or INT (average 5.46 ± 0.169 kg/d). The objectives of experiment 2 were to test how differences in diet composition can affect the chemical composition of manure and resulting methane production in an anerobic digestor. Manure samples were collected from cows in experiment 1, and a biochemical methane potential test was conducted over 2 runs averaging 32 d. Manure substrate aNDFom was higher when cows consumed RS or CON and lower when cows consumed RF or INT (43.5%, 42.9%, 40.4%, and 39.2% TS for RS, CON, RF, and INT, respectively). Treatment did not affect manure methane (average 279.7 ± 10.76 mL/g VS) or biogas production (average 444.2 ± 19.96 mL/g VS). Total manure methane potential increased when cows consumed RF or RS (1,464.4, 1,642.0, and 1,571.7 ± 48.11 L/d for CON, RF, and RS, respectively), but no difference was observed for INT (1,466.1 ± 48.11 L/d). Results of these experiments indicate that feeding DDGS in place of dietary starch, NDF, and fNDF does not affect enteric methane production, but that intake and milk production may be increased by replacing dietary NDF and fNDF. Furthermore, feeding DDGS in place of other dietary ingredients has no effect on manure methane production in an anaerobic digestor, but it may influence manure VS output and thus total manure methane potential.