Six ruminally fistulated Hereford steers (body weight=414±13 kg) were used in a switch back design to determine whether two particle sizes of alfalfa hay (18.75 and 4.65 mm theoretical cut length) influenced salivary secretion during eating. The experiment carried out in two 26-d periods, with 11-d of adaptation to ration, followed by 5 d for determining the level of voluntary feed intake, 7-d for adaptation to feeding to 90% of voluntary feed intake, and 3-d for measurements. Saliva secretion was measured during the morning meal by rumen evacuation technique at 35 minute after feeding through the rumen fistula of each steer. Coarse and fine alfalfa had the same chemical composition. The geometric mean of coarse and fine alfalfa particles during the eating time decreased by 40.62 and 45.53%, respectively. Reduction of particle size increased the functional specific gravity of alfalfa hay and particulate matter. In addition, the gas associated with particles had similar trend to the functional specific gravity. Production of saliva in milliliters (P=0.001), per kg of dry matter intake (P<0.0001) and per each kilogram of neutral detergent fiber (NDF) intake (P<0.0001) were affected by alfalfa particle size. Saliva production was higher in coarse alfalfa treatment. Reduction of alfalfa particle size reduces the ability of alfalfa forage as a physically effective fiber source in feeding of ruminant by decreasing the ability to saliva secretion.

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