The objective of this experiment was to evaluate the effects of different dietetic physical profile on the performance of lactating dairy cows. Ten Holstein dairy cows (avg. 550 kg) were allotted to a switch back experimental design in three successive periods. The animals were individually housed in a tie stall and fed with total mixed rations constituted by Tifton hay (50,4%) and concentrated (49,6%). The Tifton hay was ground in commercial miller and sieved at 3,2; 4,8; 7,9; 15,9 and 25,4 mm mesh and samples from each grinding were screened through the Particles Separator Model Penn State for the determination the profile of particle distribution. Five treatments were constituted: T1<FONT FACE=Symbol>¾</FONT>100% of particles below 8 mm; T2<FONT FACE=Symbol>¾</FONT>76% below 8 mm and 24% between 8 and 19 mm; T3<FONT FACE=Symbol>¾</FONT>36,7% below 8 mm, 26,6% between 8 and 19 mm and 36,7% above 19 mm; T4<FONT FACE=Symbol>¾</FONT>32% below 8 mm, 28% between 8 and 19 mm and 40% above 19 mm; T5<FONT FACE=Symbol>¾</FONT>26% below 8 mm, 28% between 8 and 19 mm and 46% above 19 mm. The results indicated that diet and nutrient intakes as well feed conversion were not affected by the different diet physical profile, but changes in the milk production and composition were observed. It was observed that dairy cows fed with an intermediary dietary distribution profile yielded more milk. Milk fat yielded was not affected by dietary fiber particle distribution profile however dairy cows fed with diets of higher physical profile yielded a higher milk fat content. The processing of the diet ingredients, with reduction in the particle size, should be carefully considered once the best performance response was observed when the animals were submitted to the diets with intermediary physical profile.
fiber; feed intake; dry feed conversion; physical profile; performance
