Laser methane detector-based quantification of methane emissions from indoor-fed Fogera dairy cows

OBJECTIVE: Portable laser methane detectors (LMDs) may be an economical means of estimating CH(4) emissions from ruminants. We validated an LMD-based approach and then used that approach to evaluate CH(4) emissions from indigenous dairy cows in a dryland area of Ethiopia. METHODS: First, we validated our LMD-based approach in Simmental crossbred beef cattle (n = 2) housed in respiration chambers and fed either a high- or low-concentrate diet. From the results of the validation, we constructed an estimation equation to determine CH(4) emissions from LMD CH(4) concentrations. Next, we used our validated LMD approach to examine CH(4) emissions in Fogera dairy cows grazed for 8 h/d (GG, n = 4), fed indoors on natural-grassland hay (CG1, n = 4), or fed indoors on Napier-grass (Pennisetum purpureum) hay (CG2, n = 4). All the cows were supplemented with concentrate feed. RESULTS: The exhaled CH(4) concentrations measured by LMD were linearly correlated with the CH(4) emissions determined by infrared-absorption-based gas analyzer (r(2) = 0.55). The estimation equation used to determine CH(4) emissions (y, mg/min) from LMD CH(4) concentrations (x, ppm m) was y = 0.4259x+38.61. Daily CH(4) emissions of Fogera cows estimated by using the equation did not differ among the three groups; however, a numerically greater milk yield was obtained from the CG2 cows than from the GG cows, suggesting that Napier-grass hay might be better than natural-grassland hay for indoor feeding. The CG1 cows had higher CH(4) emissions per feed intake than the other groups, without significant increases in milk yield and body-weight gain, suggesting that natural-grassland hay cannot be recommended for indoor-fed cows. CONCLUSION: These findings demonstrate the potential of using LMDs to valuate feeding regimens rapidly and economically for dairy cows in areas under financial constraint, while taking CH(4) emissions into consideration.