PS8-14. Evaluation of an Automated Head Chamber System for Measuring Gas Flux in Confined Steers.

Abstract In recent years, the use of the automated head chamber system (AHCS) has become recurrent when evaluating gas flux in ruminants. However, there is limited information regarding the determination of gas flux among AHCS units, when cattle are not exposed to all units simultaneously. The objective of this experiment was to define the effect of AHCS units on the gas flux determination of steers under confined conditions. A total of six mature Angus steers (1056 ± 72 kg of initial body weight) were used to validate the gas flux during three 14-day periods. Steers were located in a different pen during each period. Each pen contained five intake monitoring system units (SmartFeed, C-Lock, Rapid City, SD) and one AHCS (GreenFeed, C-Lock, Rapid City, SD) unit. Steers were fed ad libitum a high-forage diet of corn silage, wheat straw, dry distillers' grains, and minerals and vitamins (45, 40, 10, and 5% on a dry matter basis, respectively). Steers were allowed to visit the AHCS unit every 2 hours (up to 12 visits per day) and consume up to 6 drops of alfalfa pellet (approximately 35 g/drop) with 30-second spacing between drops. Individual intake and gas flux were analyzed with a complete randomized design with repeated measures using the MIXED Procedure of SAS (SAS Institute Inc., Cary, NC). The model included the fixed effect of the AHCS unit and the random effect of the steer. Significance was determined at P ≤ 0.05. Individual dry matter intake was not different (P = 0.18) among AHCS units, averaging 14.7 ± 0.7 kg/d. The production of carbon dioxide (CO2) and methane (CH4) was not different (P = 0.30 and 0.48, respectively) among AHCS units. Also, the consumption of oxygen (O2) did not differ (P = 0.11) among AHCS units. The AHCS units explained 10, 17, and 28% of the variation of CH4, CO2, and O2, respectively. Gas flux determination was not different among AHCS units, suggesting consistency in gas flux determination. In this experiment, AHCS and the evaluation period are confounded by design to evaluate animals not simultaneously exposed to the same AHCS units. Thus, further work is required to evaluate animals simultaneously exposed to different AHCS units.