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Co-digestion trials of beef cattle manure and waste kitchen oil (WKO) were conducted to evaluate potential increase of biogas production for a local beef farm anaerobic digester. The trials were conducted using laboratory-scale, semi-continuously loaded digesters under mesophilic conditions, with 21-day hydraulic retention time (HRT). In a preliminary test, WKO was added at 0%, 0.5%, 1.0%, 1.5%, and 2.0% by volume, each with replicate digesters (n=2), except for the 0% level, which had one digester (n=1). Methane (CH4) yield per week increased linearly with WKO levels. Populations of bacteriodetes decreased, while clostridiales and synergistales increased with the WKO levels. A second test was conducted using treatments with more replication: control (n=3), and 1.0% (n=3) and 2% (n=3) WKO levels. Methane yields of the 1.0% and 2.0% WKO levels were 79.1% and 203% higher than the control, respectively. Addition of WKO have resulted in changes of the metagenomics of the digesters. Populations of clostridiales increased, while bacteroidales and euryarchaeota methanomicrobia YC-E6 decreased with the WKO levels. The findings confirm adding low amounts (1% and 2%) of WKO as co-digestion feedstock can be an effective way to increase CH4 yield for beef operation anaerobic digestion, especially when there are available feedstock nearby. Keywords: Anaerobic digestion, Biogas, Methane, Semi-continuous digesters.

Inherently, ruminant production of methane (CH4), a greenhouse gas (GHG), causes animal energy losses. Cottonseed is a lipid source and is used sometimes to enhance energy density in cattle diets. It also can mitigate enteric CH4. Lipids release peroxides in the rumen, and antioxidants have the ability to neutralize them. Thus, a lipid and antioxidant source can benefit rumen fermentation. The aim of this study was to evaluate rumen fermentation parameters from cows fed cottonseed and vitamin E. Six cannulated cows were arranged in a replicate 3 × 3 latin square. Treatments were: 1) Control, 2) CS (30 % corn replaced by cottonseed) and 3) CSVitE (30 % corn replaced by cottonseed, plus 500 IU VitE). Results were compared by orthogonal contrast. When compared to the control diet, cottonseed inclusion reduced enteric CH4 emissions by 42 %. Production of acetate, butyrate and the acetate to propionate ratio were respectively 34 %, 47 % and 36 % lower with the cottonseed treatments. Energy lost in the rumen as CH4 and energy release as butyrate were reduced by 26 % and 32 % respectively. Propionate and intestinal energy release were, respectively, 43 % and 35 % higher with cottonseed treatments. Furthermore, as a nutritional strategy to mitigate enteric CH4, cottonseed has positive effects on short chain fatty acid (SCFA) production and gastrointestinal energy release. Vitamin E did not result in improvements in ruminal fermentation. Further studies evaluating levels of vitamin E in association with different amounts and sources of lipids are required.

High lipid concentration in ruminant diets often harms nutrient digestibility and feed intake; thus, a protected lipid and antioxidant source can be considered as an alternative for improving diet energy without putting animal production at a disadvantage. The aim of this study was to evaluate the dry matter intake (DMI), nutrient digestibility and feeding behavior of cattle fed cottonseed and vitamin E. Six cannulated cows, non-pregnant, non-lactating were distributed in a replicated 3 × 3 Latin Square design. Feed was offered ad libitum twice daily. Treatments were: 1) Control, 2) CS: 30 % cottonseed included; and 3) CSVitE: 30 % cottonseed plus 500 IU VitE included. Data were analyzed by SAS (Statistical Analysis System, v.9.3) and the significance was declared at p < 0.05. Diets with cottonseed had 22 % greater digestibility of ether extract and 9 % lower digestibility of non-fiber-carbohydrates compared to the control. Treatments with cottonseed had 13 % higher time eating, 48 % more ruminating, 34 % more chewing and 17 % lower time idling compared to the control. Molar proportion of propionate was 36 % higher and the butyrate and acetate:propionate ratio were 27 % and 30 % lower, respectively, for the cottonseed treatments compared to the control. Including cottonseed up to 30 % can be used to increase diet energy density leading to improvements in feeding behavior and ruminal parameters. The inclusion of Vitamin E did not result in benefits to cattle when it was combined with cottonseed. Further studies should be undertaken to evaluate vitamin E levels in association with different amounts and lipid sources.

Co-digestion of beef cattle manure and waste kitchen oil (WKO) was conducted using semi-continuously loaded digesters under mesophilic conditions. Nine laboratory-scale anaerobic digesters were loaded every two days during the first 45 days, to test the effects of hydraulic retention time (HRT) of 14 (n=3), 17.5 (n=3) and 21 (n=3) days. After that the 21 days HRT was used to co-digest manure with 0% (n=1), 0.5% (n=2), 1.0% (n=2), 1.5% (n=2) and 2.0% (n=2) of WKO (Test 1) by volume. The control and oil additions corresponded to 1.46, 1.70, 1.93, 2.17 and 2.40 g-VS/L/day loading respectively. Variables evaluated included biogas production, methane concentration, pH, alkalinity, ammonia and microbial community. Total biogas and methane production per week increased linearly (p A second test was conducted using three treatments with greater replications: control (n=3), and 1.0% (n=3) and 2% (n=3) WKO levels. Biogas productions per week were 85.3% and 218%, while methane yields per week were 79.1% and 203% higher than the control, for the 1.0% and 2.0% WKO levels, respectively. Linear correlations were identified between oil addition level and many variables, including total biogas yield, methane yield and methane yield per VS destroyed. Metagenomics analysis indicated that bacteria were dominant with 97.8%, and archea represented 2.2% in the community. Populations of Clostridiales were 33.3%, 35.1% and 40.6%, while Bacteroidales were 31.5%, 28.8%, and 27.6% for the control, 1% and 2% WKO levels, respectively. Euryarchaeota Methanomicrobia YC-E6 was 1.5%, 1.3%, and 1.0%, but Euryarchaeota Methanomicrobia Methanomicrobiales was 0.4%, 0.7%, and 1.0% for the control, 1% and 2% WKO levels, respectively. Adding low amount of WKO as co-digestion feedstock can be a practical and effective biogas yield improvement method for the commercial beef manure AD plant.