Protein digestion in rainbow lorikeets, Trichoglossus haematodus.

Background -- Rainbow lorikeets are nectarivorous birds whose natural diet is low in protein and relatively high in free amino acids. Protein metabolisability (PM) of egg white (EW) protein is lower in rainbow lorikeets (6.9%) than whole egg protein in white leghorn roosters (13.9%). Objective -- (1) To determine whether PM of other sources of protein fed to lorikeets is higher than that of EW. (2) To compare the general proteolytic activity (GPA) (pepsin) of the proventriculus of the rainbow lorikeet and a granivorous bird, the domestic chicken, Gallus gallus domesticus L. Design -- (1) Five lorikeets were fed one of three diets, an EW diet, an EW and casein hydrolysate (CH) diet and a commercial "lorikeet and honeyeater" (L/H) feed (Wombaroo Food Products, Glen Osmond, SA). Lorikeets were kept in metabolism cages for 3d for feed intake measurements and excreta collection. Samples were freeze dried and analysed for nitrogen. (2) The GPA of the proventriculus of three lorikeets and three chickens was measured using haemoglobin as a substrate. Outcomes -- (1) The PM (mean ± SD, n = 5) was 4.3 ± 2.6% for the EW diet, 5.6 ± 2.5% for the EW/CH diet and 7.3 ± 3.2% for the L/H feed. The PM for the EW diet was not significantly different from the EW/CH diet and L/H feed (P>0.05). (2) The GPA of the proventriculus of lorikeets at pH 1.0 was significantly lower (P<0.01) than that of the chicken at each incubation period. Conclusions -- (1) The results of the feeding experiments with lorikeets confirm that PM of artificial protein sources is low. (2) The GPA of the proventriculus of lorikeets is lower than that of the chicken. This may contribute to the low PM by lorikeets. [ABSTRACT FROM AUTHOR]