Effects of barley grain processing on extent of digestion and milk production of lactating cows.

Effects of barley processing on site and extent of digestion and milk production in dairy cows were evaluated in a 4 x 4 Latin square design with four lactating cows with ruminal and duodenal cannulas. Barley grain was steam-rolled to four thicknesses: coarse, medium, medium-flat, and flat. The processing index (PI), measured as volume weight of barley after processing expressed as a percentage of its volume weight before processing, was 81.0, 72.5, 64.0, and 55.5% for the four treatments, respectively. Diets consisted of 53% concentrate (dry matter basis) containing one of the four processed barleys. Cows were offered ad libitum access to a total mixed ration three times daily. Dry matter intake was quadratically increased with decreasing PI, with maximum intake for cows fed medium-flat barley. Although ruminal digestibilities of organic matter, starch, and crude protein were not affected by grain processing, intestinal and total tract digestibilities were linearly increased as PI of barley was reduced. Milk yield was quadratically increased (25.6, 28.1, 30.8, and 29.0 kg/d) with decreasing PI, and maximum milk yield was for cows fed medium-flat barley. Milk fat and lactose contents were similar, but milk protein content was increased with decreasing PI. These results indicate that the optimal extent of barley processing for dairy cows fed diets supplying adequate fiber was medium-flat, corresponding to a processing index of about 64%. Coarsely or flatly rolled barley is not recommended, because extensive processing did not further improve intake of digestible nutrients, and coarsely processed barley resulted in the lowest intake of digestible organic matter; hence, lowest milk production. Processing index is a reliable and practical method to quantitatively measure extent of steam rolling.