Determining Appropriate Numbers and Times of Daily Measurements Using GreenFeed System to Estimate Ruminal Methane Emission of Meat Goats

Simple Summary Methane emitted by ruminant livestock contributes to climate change and represents a considerable waste of energy. Several methane measurement devices have been developed to measure ruminal methane emission. The GreenFeed system (GFS) was introduced as a static short-term measurement device to quantify methane emission by groups of animals in pen or pasture settings. Currently, protocols are available for measuring methane emission by cattle using GFS, but none are available for goats. This study, therefore, was conducted to determine appropriate numbers (3, 4 and 6 times/day) and times of daily measurements to estimate methane emission by goats with the GFS. Also, methane emission determined with a calorimetry system (CS) was compared with that quantified with GFS. The frequency of daily measurements did not affect methane emission estimates with the GFS system, but methane emission with the GFS was much higher than with the CS. The relationship between CS and GFS, which entailed four- and six-times daily measurements, was stronger. The study suggests a protocol involving at least four daily measurements may be useful to detect treatment differences or animal ranking for methane emission. However, using the GFS for goats under the present conditions estimated higher methane emissions compared with the CS, and thus it requires modifications to improve methane-emission estimates. Abstract The study was conducted to determine appropriate numbers and times of daily gas measurements to estimate total daily methane (CH4) emission of meat goats using a GreenFeed system (GFS). A replicated 4 (four measurement protocols) × 4 (four periods) Latin square design was employed with 16 Boer wethers in a confinement pen setting. Measurement protocols entailed three (G-3T; 0600–0700, 1400–1500, and 2200–2300 h), four (G-4T; 0700–0800, 1300–1400, 1900–2000, and 0100–0200 h), and six (G-6T; 0800–0900, 1200–1300, 1600–1700, 2000–2100, 0000–0100, and 0400–0500 h) times for daily measurement periods in GFS. The fourth protocol was continuous measurement over 24 h with animals in an open-circuit respiration calorimetry system (CS). Oat hay was given in individual feeders, and a small predetermined quantity of a pelleted concentrate supplement (bait) was dispensed by the GFS or manually offered for the CS. Overall, total dry matter (DM) intake (614, 625, 635, and 577 g/day for CS, G-3T, G-4T, and G-6T, respectively; SEM = 13.9) and digestible DM intake (359, 368, 374, and 320 CS, G-3T, G-4T, and G-6T, respectively; SEM = 15.9) were lower for CS than for G-3T, G-4T, and G-6T (p < 0.05), but these variables were not different among the GFS protocols. There was a significant (p < 0.001) effect of measurement protocol on CH4 emission in g/day (11.1, 25.6, 27.3, and 26.7 for CS, G-3T, G-4T, and G-6T, respectively; SEM = 1.11), g/kg DM intake (19.3, 46.4, 43.9, and 42.4 for CS, G-3T, G-4T, and G-6T, respectively; SEM = 2.03), and g/kg body weight (0.49, 1.11, 1.18, and 1.16 for CS, G-3T, G-4T, and G-6T, respectively; SEM = 0.052), with values being much lower for CS than for G-3T, G-4T and G-6T. Conversely, CH4 emission was similar among the GFS protocols despite differences in the time and number of daily visits (2.03, 2.76, and 3.75 visits for G-3T, G-4T, and G-6T, respectively; SEM = 0.114; p < 0.001). Pearson correlation (r) analysis indicated a moderate to high (p < 0.05) correlation between CS and G-3T (r = 0.62 for CH4 in g/day and r = 0.59 for CH4 in g/kg BW), CS and G-4T (r = 0.67 for CH4 in g/day and r = 0.76 for CH4 in g/kg BW), and CS and G-6T (r = 0.70 for CH4 in g/day and r = 0.75 for CH4 in g/kg BW). However, the correlation coefficient for CH4 in g/kg DM intake was low between CS and G-3T (r = 0.11) and CS and G-6T (r = 0.31) but slightly greater between CS and G-4T (r = 0.47). In conclusion, the results suggest that CH4 emissions using GFS in a confinement setting were greater compared with the CS in goats, but CH4-emission estimation using the GFS correlated with the CH4 emission in the CS system with a stronger relationship for the four times of daily measurements.