PSX-11 Evaluation of a laser methane detector for measuring methane emissions in growing spanish goats fed different diets.

Abstract This study evaluated the use of a portable laser methane detector (LMD) as a practical method for measuring methane emissions in goats for potential on-farm applications. Thirty-six growing Spanish doelings (~12 months old, ~25 kg body weight) were assigned to a 6 × 6 Latin square design over six 3-week periods. Six forage types—alfalfa hay (AL), lespedeza hay (LS), alfalfa-lespedeza mix (AL-LS), Bermuda grass hay (BR), mixed grass hay (MG), and wheat straw (WS)—were provided at fixed proportions, making up 90, 83, 76, 69, 62, or 55% of the total diet. Correspondingly, six supplement levels (10, 17, 24, 31, 38, or 45% of the total diet) were assigned. Diets were formulated to contain ~13% crude protein. During the first two weeks of each period, animals were situated on elevated individual pens. In the third week, animals were placed in metabolic cages, and methane emissions were measured twice a day using LMDs (LMD-CH4) for a duration of one day. An additional one-day methane measurement was obtained using both calorimetry system (CAL-CH4) and LMDs while they were in calorimetry cages with a headbox. Fecal samples were collected for five days, and feed samples were taken weekly. Dry matter (DM) intake was significantly influenced by forage and supplement types (P < 0.01). Goats receiving the lowest supplement level (10%) had lower intake than those fed 24–45% supplements (537 vs. 611–655 g/day; P< 0.01), with no significant differences among the higher supplement groups. Forage type also affected intake, ranking AL, AL-LS, and BR > LS > MG > WS (703 to 472 g/day; P< 0.01). Average methane concentrations during respiration and eructation events were 29.6 and 118 ppm-m (51.2 and 206 ppm-m/kg DM intake), respectively, while methane production via calorimetry was 12.1 g/day (20.8 g/kg DM intake). Feeding AL, AL-LS, and BR resulted in ~24% lower methane concentrations (ppm-m/kg DM intake) compared to MG and WS, with values for respiration ranging from 43.9 to 51.2 vs. 57.0 to 64.3 and for eructation from 175 to 206 vs. 242 to 253. Supplementation effects on CH4 concentration (ppm-m/kg DM intake) from respiration and eructation events were significant between the 17% level and other levels. Correlations (r) between LMD-CH4 (ppm-m) and CAL-CH4 (g/day) were low to moderate (respiration: r = 0.402, P=0.015; eructation: r = 0.367, P=0.028) but slightly improved when expressed per kilogram DM intake (respiration: r = 0.456, P=0.005; eructation: r = 0.544, P=0.001). These findings suggest that LMD measurements are moderately correlated with calorimetry-based methane production and may be useful for on-farm methane production monitoring. A follow-up study with mature animals may further refine the correlation between LMD and calorimetry measurements.