Investigation on bioavailability of rumen bacterial and protozoal phosphorus using a chick-model

Ruminal bacteria and protozoa provide excellent organic phosphorus (P) sources for the host animal. This experiment was conducted to compare the bioavailability of bacterial and protozoal P in comparison with that of dicalcium phosphate (DCP) as a reference phosphorus source. Bacteria and protozoa were isolated from the rumen contents of dairy cows and the chick-model was used to determine the phosphorus bioavailability. Fifteen day-old chicks were used in a completely randomized design with 4 treatments consisting of a control diet (without P, as a basal diet), bacterial P+basal diet, protozoal P+basal diet, and DCP+basal diet. Phosphorus balance was selected as the response criterion for phosphorus bioavailability assessment, using multiple linear regressions. The results showed a higher phosphorus bioavailability of protozoal P and DCP compared with bacterial P (P < 0.05); with no significant difference between protozoal P and DCP. Relative phosphorus bioavailability values of bacterial source ranged from 0.451 to 0.495, using protozoal source as reference. Bioavailability of P in rumen protozoa, relative to that in DCP, was high (approximately 97%); therefore rumen protozoa may serve as an important source of organic P in ruminants for providing a significant portion of phosphorus requirements.