ESTIMATION OF APPARENT METABOLIZABILITY IN HERBIVOROUS WILDFOWL WITH PLANT PIGMENTS

If the feeding habitat requirements of herbivorous wildfowl are to be understood completely, then knowledge of plant metabolizability is ess ential. Use of a suite of plant pigments or chromogen as a naturally o ccurring indigestible marker to estimate apparent metabolizability (AM ) in free-ranging herbivorous wildfowl is assessed as a simple, inexpe nsive, and potentially accurate method. The analytical procedure is de scribed and 3 stages identified as possible areas that could give rise to inconsistent AM estimates. These stages were examined accordingly and as a result the following recommendations made: (1) food and fecal samples collected in the field must be frozen quickly, (2) samples to be analyzed should be freeze-dried, not dried in an oven or vacuum ov en, and (3) light must be excluded from the chromogen extracts once in solution. Once the procedure had been verified, AM of cut grass eaten by a captive brent goose (Branta bernicla) was measured directly (by measuring ingestion and egestion) and indirectly (by measuring chromog en concentrations in freeze-dried food and fecal samples). Results of AM given by the 2 methods were in close agreement. Recovery of chromog en in the feces was 101.3 +/- 11.2% (mean +/- SD, n = 3) indicating th at chromogen can be used to estimate AM for free-ranging geese and her bivorous ducks, but variation was high and sample size small and so fu rther trials would be valuable to consolidate this result.