The effects were examined of corn grain particle size and the ionophore lasalocid on performance, blood parameters, and nutrient digestibility of early lactation cows. Smaller corn particle size was expected to result in faster rate of digestion and ruminal fermentation of starch. Eight multiparous and 4 primiparous cows in early lactation were fed diets (44% forage) with cracked or ground, dried shelled corn grain and with or without lasalocid (360.mg/d per cow). The experiment was a replicated (n = 3) 4 x 4 Latin square design with 21-d periods and a 2 x 2 factorial arrangement of treatments. Lasalocid tended to improve DMI. Lasalocid and ground corn decreased body condition loss and milk fat and increased milk protein. Ground corn tended to increase milk yield but had no effect on 4% FCM, lactose, and BW. For all cows, milk yield, 4% FCM, lactose, and BW were unaffected by lasalocid; however, subsequent analysis of individual squares revealed that milk yield of primiparous cows increased with lasalocid. Ground corn increased total tract starch digestibility and decreased NDF digestibility. Interactions between lasalocid and particle size of corn grain were observed only for change in serum insulin concentration before and after meals.
