Abstract
UNLABELLED
The Kakapo, a large NZ native parrot, is under severe threat of extinction. Kakapo breed only in years when the local podocarps, including rimu (Dacrydium cupressinum), are fruiting heavily, and the fruit are the preferred food both in the diet of breeding females and for provisioning chicks. Attempts to provide a supplementary food during years of poor fruit supply have failed to encourage breeding. Nutrient analysis of rimu berries reveals high calcium content (8.4mg/g dry matter) which would be essential for both egg shell production and the growing skeleton of the chick. Vitamin D is also critical for these processes and for the maintenance of calcium homeostasis, but the source of vitamin D for these nocturnal, ground-dwelling vegetarians is unknown.
OBJECTIVE
To examine the vitamin D status of adult Kakapo, and to investigate the possibility that rimu berries provide vitamin D as well as calcium, thus differentiating them from the supplementary foods provided to date.
METHOD
Previously collected and frozen serum from 10 adult birds (6 females, 4 males) was assayed for 25(OH)D3 and D2. Two batches of previously frozen rimu berries were analysed for vitamin D3 and D2.
RESULTS
Vitamin D status of the 10 adult birds was very low; mean 4.9nmol/l, range 1-14nmol/l 25(OH)D3. No 25(OH)D2 was detected in any of the birds. High levels of D2 and moderate levels of D3 were found in the rimu berries.
CONCLUSION
Traditionally it has been considered that the D3 isoform of this endogenously produced secosteroid is produced only in animals. However, D3 has been reported in the leaves of plants of the Solanacae family (tomato, potato, capsicum). The avian vitamin D receptor (VDR) is thought to have a much greater affinity for the D3 form. Therefore if rimu fruit are able to provide breeding Kakapo with D3, and are a plentiful source of calcium, they could be the perfect food package for breeding and nesting birds. Of wider importance, this finding challenges conventional understanding that D3 production is exclusive to animals, and that there are no high concentration food sources of vitamin D.
Collapse