Digestibility of Critical Care Diets and Nitrogen Balance in Oiled Common Murres (Uria aalge) and Western Grebes (Aechmophorus occidentalis) Received for Rehabilitation in California
Nutritional support is a primary therapy administered to animals during responses to oil spills, but data informing nutritional decision-making during events is limited. Common murres and western grebes naturally oiled by oceanic seeps off Ventura and Santa Barbara counties, CA, USA were assigned to diets with varying levels [5.8% (no added oil), 11.0%, and 20%] and types of oil (corn, salmon) added to a partially purified basal dieta. Birds ranged from extremely emaciated to thin (62–80% wild mean mass). We assessed nitrogen retention (NR), apparent nitrogen digestibility (ApND), nitrogen-corrected apparent metabolize energy (AMECn), energy digestibility (ED), fat digestibility (FD), and estimated fat excretion (FE) through use of acid insoluble ash as an indigestible marker. Fat excretion is important in these species, because once birds have been cleaned they are at risk of re-contamination during care. Lower-fat diets resulted in higher NR, higher ApND, higher AMECn, and lower FE. NR and FE were found to have a negative relationship, where decreases in nitrogen retention were significantly related to increases in fat excretion. ED significantly declined with declines in body mass regardless of diet, suggesting severity of emaciation reduced birds’ ability to extract energy from food. ED was highest in the 11% salmon oil diet; hence, this diet had the highest effective energy content despite lower gross kcal/kg diet. Diets fed during oil spills historically have had high fat concentrations in an effort to provide maximum caloric support; however, results of this study suggest lower-fat diets may be more efficacious.
a. Emeraid Piscivore, Lafeber Company, Cornell, IL, USA
This project was supported by the California Department of Fish and Wildlife’s Oil Spill Response Trust Fund through the Oiled Wildlife Care Network at the Wildlife Health Center, School of Veterinary Medicine, University of California, Davis. Many thanks to the staff and volunteers of International Bird Rescue who cared for these animals and assisted with feeding and sample collection. Special thanks to Ted Lafeber for his generosity in donating specially mixed diets for this study.