Development of a Mobile Open-Circuit Respiration Head Hood System for Measuring Gas Exchange in Camelids in the Andean Plateau

**Background:** Alpacas are economically vital to Andean Plateau communities, yet data on their energy metabolism and methane emissions are extremely scarce. The IPCC guidelines lack methane conversion factors for South American camelids, and existing nutritional requirements are extrapolated from goats, sheep, and cattle. No gas exchange measurement facilities existed in Peru for camelids prior to this study. The authors aimed to build and validate a mobile open-circuit respirometry system (head hood) for measuring O₂ consumption, CO₂ and CH₄ production, and heat production (HP) in alpacas, and to conduct an experimental test comparing two methods of HP determination.

**Methods:** A mobile open-circuit respirometry system was constructed based on Fernández et al., consisting of a metabolic crate, head hood (510 L volume, galvanized plate with acrylic window), gas analyzers (infrared for CH₄ and CO₂, paramagnetic for O₂), mass flowmeter, gas cooler, and data logging system. System calibration was performed via two recovery tests: (1) controlled release of pure CO₂ measured gravimetrically, and (2) ethanol burning to assess both O₂ consumption and CO₂ recovery. Eight Huacaya male alpacas (58.3 ± 3.30 kg BW) were fed a 30:70 alfalfa pellet:oat hay diet at a level close to estimated MEm (323 kJ/kg BW⁰·⁷⁵). After a 21-day adaptation period, feed intake, feces, and urine were collected over 3 days. Gas exchange was measured sequentially for 24 h per alpaca. HP was calculated by the Brouwer equation (RQ method) using O₂ consumption, CO₂ and CH₄ production, and urine nitrogen. Independently, HP was determined by carbon-nitrogen balance (CN method). Fasting HP was measured in 5 alpacas after 3 days of fasting (20 measurements of 20 min each). MEm was estimated by two approaches: correction to zero energy retention using kf, and linear regression of RE against MEI.

**Key Results:** Recovery tests showed excellent accuracy: 104 ± 2% for controlled CO₂ release (R² = 0.997), and 98.5 ± 4.7% for CO₂ and 102.2 ± 4.7% for O₂ via ethanol burning. Repeatability was 70% for CH₄ and 60% for HP measurements. Mean HP by RQ method was 402 kJ/kg BW⁰·⁷⁵ (range 384–414) and by CN method was 398 kJ/kg BW⁰·⁷⁵ (range 381–411), with no significant difference (p > 0.05). The discrepancy between methods averaged 0.85%. Regression of HP(RQ) vs. HP(CN) yielded R² = 0.9752 with low residual standard error. Fasting HP was 250 kJ/kg BW⁰·⁷⁵. Using the zero energy retention correction, MEm was 323 kJ/kg BW⁰·⁷⁵ with efficiency (km) of 0.77. By linear regression (RE = −252 + 0.68 × MEI), FHP was 252 kJ/kg BW⁰·⁷⁵, km = 0.68, and MEm = 369 kJ/kg BW⁰·⁷⁵. Mean CH₄ production was 16.7 g/d (range 13–21), equivalent to 18.4 g/kg DMI. The methane conversion factor (Ym) averaged 5.5% (range 4.3–6.8%). Mean MEI was 473 kJ/kg BW⁰·⁷⁵, and mean RE was 71 kJ/kg BW⁰·⁷⁵ (RQ method) or 74 kJ/kg BW⁰·⁷⁵ (CN method).

**Clinical Implications:** This study provides the first validated mobile respirometry system for camelids in Peru, enabling field-based measurements of energy metabolism and GHG emissions. The findings confirm that alpacas have a lower basal metabolic rate than small ruminants—FHP of 250 kJ/kg BW⁰·⁷⁵ vs. 296–332 kJ/kg BW⁰·⁷⁵ for sheep and goats per NRC—consistent with adaptation to harsh Andean conditions. The MEm values (323–369 kJ/kg BW⁰·⁷⁵) are lower than those for sheep (300–447 kJ/kg BW⁰·⁷⁵) and goats (431–456 kJ/kg BW⁰·⁷⁵). The Ym of 5.5% is below the IPCC Tier 2 default of 6.5% for ruminants, suggesting that current IPCC guidelines may overestimate enteric methane emissions from camelids. These data are critical for refining national GHG inventories and establishing species-specific nutritional recommendations for alpacas, which currently rely on extrapolated ruminant data. Further research under actual Andean Plateau conditions is needed to improve accuracy.