Comparison Between the Sulfur Hexafluoride Tracer Technique and the Portable Automated Head Chamber System for Measurements of Enteric Methane Fluxes in Mid-Lactation Holstein Cows

Abstract Text:

The objective of this study was to evaluate the concordance correlation coefficient (CCC) and coefficient of variation (CV) of enteric methane flux (Q_CH4) between the sulfur hexafluoride tracer technique (SF₆) and the portable automated head chamber system [The GreenFeed (GF); C-Lock Inc., Rapid City, SD]. Eleven multiparous and 4 primiparous lactating Holstein cows housed in a tie-stall barn and averaging 176 ± 34 DIM, 42.9 ± 6.8 kg of milk yield and 681 ± 48 kg of BW were blocked by DIM, parity, and DMI (as % of BW) and, within each block, randomly assigned to 1 of 2 treatments: ad libitum intake (AI) or restricted intake (RI) (90% DMI) according to a crossover design. Each experimental period lasted 22 d with 14 d for treatments adaptation and 8 d for data and samples collection. Diets contained (DM basis): 40% corn silage, 12% grass-legume haylage and 48% concentrate. Five-minute measurements were taken from all animals with intervals of 12 h between the 2 daily samplings using the GF. Sampling points were advanced 2 h from one day to the next to yield 14 gas samplings/cow over 7 d to account for diurnal variation in Q_CH4. For the SF₆ method, sampling was done twice a day before milking times with canisters placed in 5 different locations inside the barn for measuring background gas concentration. Animal performance data were analyzed using the MIXED procedure of SAS while the comparison between methods was done using the CCC. Data inclusion criteria were a minimum of 5 measurements per animal per period and Q_CH4 ranging from 150 to 800 g/d. There was a significant difference in DMI between treatments (23.7 vs. 22.3 kg/d for AI and RI, respectively) but no difference was found for milk yield and Q_CH4 when using the GF system (471 vs. 458 g/d for AI and RI, respectively) or the SF₆ technique (406 vs. 409 g/d for AI and RI, respectively). Between animal Q_CH4 CV averaged 14.5% (GF) and 36.5% (SF₆); within animal Q_CH4 CV averaged 17.8% (GF) and 36.2% (SF₆). The CCC was 0.15 on 225 comparisons of 2 daily data points with error terms of 10% (central tendency), 17% (regression), and 73% (disturbance). Current results suggest that the SF₆ technique was twice more variable and yielded lower Q_CH4 compared with the GF system. Poor concordance between these 2 methodologies warrants further investigations.

Keywords: Methane, SF₆, GreenFeed