[en] The study was conducted to investigate the effects of a total mixed ration (TMR) particle size on digestibility and production performances of the high-yielding cows in early lactation. The treatments were TMRs with forage-toconcentrate ratio 43:57 in diet dry matter, with four different mean particle lengths and physically effective fiber (PENDF) content based on different cut length of corn silage and alfalfa haylage. Determined values of PEF (physical effectiveness factor) and PENDF (through original and modified Penn State Particle Separator, PSPS) were considerably higher for forages and TMRs using the modified PSPS. The cut length of forage and particle size of TMRs did not affect dry matter intake. However reduced forage cut length significantly increased the apparent total tract digestibility of NDF (from 53.9 to 58.66%), and crude protein (from 71.56 to 77.90%), with the decrease in the non-fiber carbohydrate digestibility (from 91.99 to 86.80%). The increase in the milk yield (35.62 vs. 38.36 kg), and decrease in the milk fat (3.50 vs. 3.10%) and protein content (3.11 vs. 2.99%) were observed with the reduction of particle size in forages. There was no effect on milk fat daily yield, but the increase of the milk protein yield (1.08 vs. 1.15 kg) was determined with the reduced forage cut lengths. The milk fat to protein ratio had tendency to decrease with the reduced forage cut length. Decrease in forage particle size improved feed conversion ratio for milk production, improved digestibility and the milk yield, whereas milk protein content was reduced

[es] Se investigaron los efectos producidos por el tama&ntilde;o de las part&iacute;culas en una raci&oacute;n total mezclada (TMR) en la digestibilidad y en las caracter&iacute;sticas productivas de vacas lecheras de alta producci&oacute;n en su primera fase de la lactaci&oacute;n. Los tratamientos fueron TMRs en una proporci&oacute;n forraje:concentrado 43:57, con cuatro diferentes longitudes de part&iacute;culas y de contenido de fibra f&iacute;sicamente efectiva (PENDF), que var&iacute;an seg&uacute;n la longitud de corte del ensilaje de ma&iacute;z y de heno de alfalfa. Los valores de PEF (factores de efectividad f&iacute;sica) y de PENDF (calculados con el separador de part&iacute;culas de Penn State, PSPS, tanto original como modificado) fueron mayores para forrajes y TMRs cuando se us&oacute; la versi&oacute;n modificada del sistema PSPS. Tanto la longitud de corte del forraje como el tama&ntilde;o de part&iacute;cula de la TMR no afectaron al consumo de materia seca, mientras que la reducci&oacute;n del tama&ntilde;o de part&iacute;cula del forraje produjo un aumento de la digestibilidad de la fibra neutro detergente y de la prote&iacute;na bruta, as&iacute; como una disminuci&oacute;n de la digestibilidad de los carbohidratos no fibrosos. Asimismo, se detect&oacute; un incremento de la producci&oacute;n de leche y una reducci&oacute;n del contenido de grasa y prote&iacute;na en la leche. La reducci&oacute;n en la longitud de corte del forraje no afect&oacute; a la producci&oacute;n diaria de grasa l&aacute;ctea, pero aument&oacute; la producci&oacute;n diaria de prote&iacute;nas en la leche. La relaci&oacute;n entre el contenido de grasa y prote&iacute;na en la leche tendi&oacute; a descender cuando se redujo el tama&ntilde;o de picado del forraje. La reducci&oacute;n del tama&ntilde;o de part&iacute;culas de forraje mejor&oacute; el &iacute;ndice de conversi&oacute;n de la materia seca del alimento para la producci&oacute;n de leche (6,8%), mejor&oacute; su digestibilidad y la producci&oacute;n, pero redujo el contenido de prote&iacute;nas.