Evaluation of an enteric methane emissions measurement system for cattle

Abstract Text: Growing concern about climate change and sustainability has increased societal pressures toward livestock production to quantify and reduce its environmental impact. Through enteric fermentation, ruminants produce the greenhouse gas methane (CH₄), and to improve emission inventories and evaluate mitigation techniques, several methods (i.e. whole animal and head chambers, SF₆ tracer technique) of measuring emissions have been developed. The objectives of this study were to evaluate a ventilated head box system capable of measuring CH₄ and carbon dioxide (CO₂) emissions, and oxygen (O₂) consumption from cattle and to compare emissions across ad libitum and restricted intake periods. An additional objective was to provide insight to animal comfort while housed in the head box system. Six Holstein heifers (n=6), initial live weight between 364 and 430 kg, were used to measure CH₄ and CO₂ emissions and O₂ consumption from two ad libitum intake periods (ADAPT and ADLIB) and one period (RESTRICT) with intake restricted to 2% of body weight on a dry matter basis. In the head box system, ambient air was circulated around the animal’s head, and expired air was collected. Emissions were determined by calculating the difference in gas concentrations between ambient and expired air. As a measure of comfort in the head box system, all cattle were assessed for lying time, and respiration rates and THI were evaluated for thermal comfort. During ADAPT and ADLIB, DMI in individual pens (10.40 ± 0.41 kg and 11.00 ± 0.41 kg, respectively) was higher (P < 0.0001) than DMI during gas measurement (9.20 ± 0.45 kg and 9.80 ± 0.45 kg, respectively). During RESTRICT, DMI in individual pens (8.40 ± 0.44 kg) did not differ (P > 0.05) from DMI during gas measurement (8.40 ± 0.45 kg). Methane and CO₂ emissions were lower (P < 0.05) during RESTRICT as compared to ADAPT and ADLIB (Table 1). Oxygen consumption rates differed for each period (Table 1). Lying time while in the head box system was similar to lying behaviors of dairy heifers reported in previous literature. There was no difference (P > 0.05) in THI and respiration rate across all periods, and THI and respiration rate were positively correlated (R² = 0.381; P < 0.0001). The head box system evaluated will be useful in examining the effects of emissions mitigation strategies, and variation in emissions caused by different feeds and throughout the 24-hour cycle of a day.

Keywords: Enteric Methane, Measurement, Cattle