UC Davis

Cattle and their waste products are considered a major source of greenhouse gas (GHG) emissions. In the United States, animal agriculture accounts for 38% of methane (CH4) emissions with 28% arising from enteric fermentation, and 10% from manure management. With California being the leading dairy state in the United States, it is increasingly important that strategies for reducing gaseous emissions in lactating dairy cows and management of their waste within the state be investigated. In studies 1 and 2, the objective was to determine the efficacy of various commercially available plant secondary metabolites (PSM) at reducing GHG and ammonia (NH3) emissions without negatively impacting the productive performance of dairy cows. The PSM’s investigated were: (1) a commercial essential oils blend comprised of eugenol, coriander seed, and geranyl acetate (Agolin® Ruminant; Agolin SA, Bière, Switzerland), and (2) a commercial blend of quebracho and chestnut tannins with saponins (SilvaFeed® BX; SILVATEAM SpA, San Michele Mondovì, Italy). In each study, twenty early- to mid-lactation Holstein dairy cows were blocked by days in milk and parity in a randomized complete block design, and were assigned one of two treatments: PSM or control (n=2/block). Cows were individually fed, group-housed in a free-stall pen, and were milked twice daily. The treatments were administered as a top dress at each of two feedings per day. Cows were sampled for enteric CH4, carbon dioxide (CO2), nitrous oxide (N2O) and NH3 emissions in head chambers (HC) for 12 hours on treatment days 0, 14, 28, 42, and 56 in study 1, and 0, 16, 32, and 48 in study 2. Enteric GHG and NH3 emissions, energy-corrected milk (ECM; kg), milk component yields (kg) and proportions (%), and dry matter intake (DMI; kg) were analyzed for pairwise comparison in R. In study 1, supplemental Agolin® tended to decrease enteric N2O intensity, and significantly decreased enteric CH4 and NH3 intensity (g or mg gas/d/kg ECM). Enteric NH3 production decreased significantly with Agolin supplementation, though there was no effect on CH4, CO2, or N2O production (g or mg gas/d). Enteric GHG and NH3 yields (g or mg gas/d/kg HC DMI) did not differ between treatment types in study 1. In study 2, SilvaFeed® BX tended to decrease enteric CH4 and CO2 production (g/h), significantly decreased N2O production (mg/h), and tended to increase NH3 production (mg/h). Supplementing cows with SilvaFeed BX resulted in an increase in slurry NH3 emissions (mg/h/m2), though the GHG’s were unaffected. No differences were found in ECM, milk fat yield, milk protein yield, and DMI in PSM-fed cows in both studies 1 and 2. Study 3 investigated the ability of a commercial biological wastewater applicant (BiOWiSH® AQUA; BiOWiSH Technologies Inc., Cincinnati, Ohio) for reducing NH3 emissions in the effluent from anaerobic digesters. Effluent was collected from an anaerobic digester and was homogenized and distributed equally between 18 steel drums. The drums were placed in a 6x3 (row x column) grid with treatments allocated and applied according to a double Latin square. Treatments were comprised of positive control (aeration but no BiOWiSH), negative control (no aeration and no BiOWiSH), and the experimental treatment (both BiOWiSH and aeration). Gaseous emissions were measured continuously across 56 days, with each column being measured for 24 hours every 3-4 days. Ammonia emissions did not significantly differ between the experimental treatment and the positive control. Both the experimental treatment and the positive control had higher NH3 emissions than the negative control. Future research should assess the mitigation potentials of each of the feed additives and the applicant at varying dosage levels.