Assessment of excreta collection methods to estimate true metabolizable energy of waterfowl foods in wild ducks

Abstract

True metabolizable energy (TME) of waterfowl foods is commonly estimated for use in energetic carrying capacity models in association with conservation planning efforts under the North American Waterfowl Management Plan. Researchers define and estimate TME as the net energy from excreta collected from an individual after feeding a precise quantity of a food item compared with excreta collected during a fasted control. We evaluated an alternative excreta collection method for use in TME assays for comparison with traditional excreta collection methodology for waterfowl. We fed widgeongrass (Ruppia maritima) to wild‐caught mallards (Anas platyrhynchos) during autumn 2016 at Forbes Biological Station, Havana, Illinois, USA, and quantitatively collected excreta using a harness‐style excreta collection method and a traditional basin‐style collection method. We were unable to find support for a difference in total excreta energy, mass loss, and TME estimates between collection methods, but high variation in TME among samples prohibited our ability to consider the collection methods similar. Time required for processing harness samples was 60–175 minutes less per sample than for basin samples. The basin method has been the standard for TME trials on waterfowl, but we found the harness method to be much more efficient and potentially allow for better animal husbandry practices. We suggest the harness method be tested further with increased sample sizes or alternate foods prior to widespread application, but researchers conducting TME assays of waterfowl foods should consider using this method in the future. © 2019 The Wildlife Society.

Variation in True Metabolizable Energy Among Aquatic Vegetation and Ducks

“…Following precision feeding, we collected excreta for an additional 48 hours using either a metabolic cage method ( n = 121; McClain 2017) or harness‐style excreta collection method ( n = 75; Adeola et al 1997, Adeola 2006). Both methods produced similar TME N estimates, but the harness‐style method was more time and cost efficient (Lancaster et al 2019). The metabolic cage method consisted of placing a bird in a cage (20 cm × 20 cm × 30 cm, 1‐cm vinyl‐coated welded wire mesh) and suspending the cage inside a plastic tub (~42 cm × 36 cm × 31 cm), which collected excreta.…”

“…The metabolic cage method consisted of placing a bird in a cage (20 cm × 20 cm × 30 cm, 1‐cm vinyl‐coated welded wire mesh) and suspending the cage inside a plastic tub (~42 cm × 36 cm × 31 cm), which collected excreta. The harness‐style method consisted of attaching a 480‐ml Whirl‐pak bag over a duck's cloaca using a custom harness, which remained attached for 48 hours after feeding (Lancaster et al 2019). We placed ducks with harnesses in clear, plastic trial tubs (as previously described) in case of Whirl‐pak bag failure.…”