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.