Claudiney de Jesus Couto ¹ Bruna Cardoso Braga ² Raphael dos Santos Gomes ³ Wagner Pessanha Tamy ⁴ Severino Delmar Junqueira Villela ¹ Fernando de Paula Leonel ^5*

• ¹ Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM), São Paulo, São Paulo, Brazil
• ² Universidade Federal de Goiás, Goiânia, Goiás, Brazil
• ³ Instituto Federal de Educação, Ciência e Tecnologia de Rondônia - IFRO, Porto Velho, Rondônia, Brazil
• ⁴ Faculdade de Medicina Veterinária da Universidade Federal Fluminense, Icaraí Niterói, Brazil
• ⁵ Universidade Federal de São João del-Rei, São João del Rei, Brazil

The objective was to compare the potential of different sources of phosphorus in promoting improvement in fiber digestibility parameters. Feeds low in phosphorus were chosen to compose the basal diet. Five crossbred heifers with an average initial weight of 150 ± 8.2 kg were used, randomly distributed in a 5x5 Latin square. The treatments were: negative control (NC) without supplementary phosphorus; dicalcium phosphate from igneous rock with sulfuric acidulation, neutralization with limestone, and the physical form of microgranules (ISLG); Dicalcium phosphate from igneous rock with sulfuric acidulation, neutralization with hydrated lime, and the physical form of powder (ISLhP); Dicalcium phosphate from sedimentary rock with hydrochloric acidulation, neutralization with limestone, and the micro-granulated physical form (SeCLG); Dicalcium phosphate from the monocalcium phosphate and hydrated lime reaction adjusted with phosphoric acid, and the powder physical form (MLhPaP). The parameters of the kinetics transit of particles with use of the chromium marker, fixed to the roughage cell wall and subsequent recovery of the marker in the heifer feces, were determined. The ISLG resulted in a higher (p<0.05) passage rate of particles from the solid to the liquid phase in the rumen-reticulum. There was no difference (p>0.05) between the diets for the time that indigestible particles spent from ruminal escape to their first appearance in feces. The longest retention time (p<0.05) of solid particles in the rumen-reticulum was detected in animals that received NC diet. The DMI of heifers that received ISLG and SeCLG did not differ from each other (p>0.05) and were higher (p<0.05) than the DMI of heifers that received ISLhP MlhPaP, NC, which also did not differ from each other (p>0.05). In conclusion, heifers that do not receive supplemental phosphorus exhibited poorer fiber processing and dry matter intake (DMI).