UC Davis

The present thesis consists of two chapters. The first chapter focuses on reviewing previously conducted research pertaining to reducing direct, enteric methane (CH4) emissions from the California beef cattle industry to meet state regulatory goals and climate neutrality. The second chapter constitutes a study aimed to reduce enteric CH4 production through the use of a tannin containing feed additive. Forty-eight black Angus and black Angus x Herford heifers (body weight (BW) = 592 kg ± 11.0) were used in a randomized complete block design (n=24) and blocked based on individual, co-variate CH4 (111.0 g ± 7.2) emissions collected on day (d) -18 to -15. The two treatments that were used in this study were as follows: Control (CON; 48.87 g of ground corn/hd/d + 1.13 g Melengestrol Acetate (MGA; g/hd/d; Zoetis, Parsippany, NJ)) and Quebracho condensed tannin (TAN; 0.15% of dry matter (DM) + 48.87 g of ground corn/hd/d + 1.13 g MGA). Heifers were precision fed based on 2.2% BW and % DM of the total mixed ration (TMR) being fed. Individual dry matter intake (DMI) and water intake (WI) were monitored using the Roughage Intake Control System (RIC System; Hokofarm Group, Marknesse, The Netherlands). Enteric CH¬4, carbon dioxide (CO2), and hydrogen (H2) gas emissions were collected using the Green Feed (GF; C-Lock, Inc, Rapid City, SD). Enteric emissions were collected on d 10-13, 24-27, 38-41, 52-55, and on d 66-69. Sixteen, 3-hour sampling windows were staggered across a 90-hour sample period to collect a total of eight emission readings/animal/sampling period to determine the average 24-hour emission production from each individual heifer. Heifers were harvested on d 76, and individual carcass data was collected on d 77. Methane, CO2, and H2 production did not differ between TAN vs. CON heifers (P > 0.05). Methane and H2 yield were similar between TAN and CON fed heifers (P > 0.05). Carbon dioxide yield had a tendency (P = 0.075) to be reduced from heifers fed TAN vs. CON by 7.47% from d 38 to 41 (Table 15). Quebracho condensed tannin did not have an effect on enteric CH4, CO2, and H2 intensity in TAN fed heifers vs. CON fed heifers (P > 0.05). Body weight and average daily gain (ADG) were similar between heifers fed TAN vs. CON (P > 0.05). There were no differences between heifers fed TAN and heifers fed CON for gain to feed ratio (G:F), DMI, and WI (P > 0.05). Hot carcass weight (HCW), marbling score, preliminary yield grade (PYG), ribeye area (REA), and dressing percentage (DP) were similar between TAN and CON heifers (P > 0.05). All carcasses graded either Prime or Choice. In summary, precision supplementation of TAN at 0.15% of DM to feedlot heifers consuming a high concentrate did not affect enteric gas emissions, animal performance, and carcass characteristics and quality.