LASALOCID AND PARTICLE-SIZE OF CORN GRAIN FOR DAIRY-COWS IN EARLY LACTATION .1. EFFECT ON PERFORMANCE, SERUM METABOLITES, AND NUTRIENT DIGESTIBILITY

The effects were examined of corn grain particle size and the ionophor e lasalocid on performance, blood parameters, and nutrient digestibili ty 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 a nd 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 yi eld but had no effect on 4% FCM, lactose, and BW. For all cows, milk y ield, 4% FCM, lactose, and BW were unaffected by lasalocid; however, s ubsequent analysis of individual squares revealed that milk yield of p rimiparous cows increased with lasalocid. Ground corn increased total tract starch digestibility and decreased NDF digestibility. Interactio ns between lasalocid and particle size of corn grain were observed onl y for change in serum insulin concentration before and after meals.