Malabsorption syndrome (MAS) is a multifactorial disease that causes intestinal disorders due to different infectious agents, such as viruses or bacteria. In broilers, MAS is characterised by poor growth, retarded feathering, diarrhea, pigment loss, bone abnormalities as well as increased mortality and it causes considerable losses to the poultry industry. Furthermore, it is known that during episodes of MAS fat-soluble vitamins, such as vitamin D₃ are almost not absorbed, which may result in partial or even severe deficiency of these important micronutrients. Recently 25-hydroxycholecalciferol (25- OH-D₃), the first metabolite of vitamin D₃, has become commercially available under the trade name Hy•D.

The aim of this study was to investigate, whether the vitamin D₃ status was better, when feeding broilers with Hy•D instead of vitamin D₃ and whether positive effects on their health, particularly on the quality of the bones, could be observed. Day-old broiler chicks were supplemented either with vitamin D₃ (2,760 IU/kg) or Hy•D (69 mcg/kg) via the feed and inoculated either with saline or with MAS on the day of hatch. Weight gain of inoculated chicks was significantly impaired, when compared with the non-challenged groups. Within the inoculated treatments the Hy•D supplemented chicks achieved statistically the highest weight gain from day 8 to 29. MAS severity, however, was not reduced by Hy•D; the appearance of clinical signs such as cystic crypts or crypt degeneration rather seemed to be delayed.

The highest plasma levels of 25-OH-D3 were measured in the non-challenged broilers, supplemented with Hy•D. Plasma 25-OH-D₃ of the challenged Hy•D chicks was similar to the non-challenged birds, supplemented with vitamin D₃, while plasma 25-OH-D₃ in the challenged chicks on vitamin D₃ was low at day 3 and non-detectable thereafter. These findings indicate that Hy•D is absorbed differently from vitamin D₃, assuring physiological blood 25-OH-D₃ levels even during bouts of severe malabsorption. Bone strength was numerically improved with Hy•D versus vitamin D₃ in both, the inoculated and the non-inoculated groups. In conclusion, the supplementation of Hy•D to MAS challenged broiler chicks improved their performance and their vitamin D₃ status, as measured by plasma 25-OH-D₃.