The efficacy of a standardised product from dried leaves of Solanum glaucophyllum as source of 1,25-dihydroxycholecalciferol for poultry

Abstract

1. Chemical characterisation of an extract of Solanum glaucophyllum (SG) leaves affirmed the predominant presence of 1,25-dihydroxycholecalciferol (1,25(OH)₂D₃) glycosides. The compound 1-(ß-D-glucopyranosyl)-1α,25-dihydroxycholecalciferol was isolated for the first time from a natural source.

2. Vitamin D activity of the extract was confirmed by the calcaemic properties shown in a quail eggshell bioassay. The results suggested a 1,25(OH)₂D₃ bioavailability of approximately 15%.

3. A broiler feeding experiment replicated in time was carried out with 6 treatments. A basic control diet containing 25 μg cholecalciferol/kg was supplemented with 2.5 and 5 μg free 1,25(OH)₂D₃/kg, with a product based on dried SG leaves (Panbonis) providing 10 μg of 1,25(OH)₂D₃-glycosides/kg, with two concentrations of an SG extract providing 8.8 and 37.8 μg of 1,25(OH)₂D₃-glycosides/kg.

4. Tibia breaking strength and stiffness were numerically greater in all treatment groups with free 1,25(OH)₂D₃ and with SG products compared to controls, though the overall treatment effects only had probabilities in the range of P = 0.07 to P = 0.1. Values for both characteristics increased progressively, with additions of synthetic 1,25(OH)₂D₃; values with the dried SG product were similar to those with 5 μg synthetic 1,25(OH)₂D₃/kg.

5. Plasma calcium was mildly elevated (P < 0.05) in treatment groups. The SG extract treatment containing 37.8 μg 1,25(OH)₂D₃/kg gave the highest plasma calcium concentration and lowest bodyweight, signs of marginal hypervitaminosis D. Plasma 1,25(OH)₂D₃ concentrations were in the normal range for all treatments.

6. Tibial dyschondroplasia occurred in only one replicate. The incidences were 31% in controls but considerably lower or zero with all other treatments.

7. Bioavailability of 1,25(OH)₂D₃ in the SG product seemed to be higher in broiler chickens than in Japanese quails.

8. It is concluded that the inclusion of the dried SG product as a source of vitamin D₃ in broiler diets at a dietary concentration of 1 g/kg, providing 10 μg 1,25(OH)₂D₃/kg, is safe and efficacious.

ACKNOWLEDGEMENTS

The authors thank Prof. R. Boland, Departamento de Biologia, Bioquimica y Farmacia, Universidad Nacional del Sur, Bahia Blanca, Argentina, for his very helpful advice in plant collection and Mr R. Fleming and Mrs L. McTeir, Roslin Institute, for assistance with the broiler study. The Swiss Commission for Technology and Innovation CTI grant supported the preparative work.