Composition of Milk Produced on Pelleted Hay and Heated Corn

Abstract

Summary Eight lactating cows were fed rations of (A) long hay plus heated (flaked) corn, (B) long hay plus ground corn, (C) ground, pelleted hay plus heated corn, and (D) ground, pelleted hay plus ground corn in a 4×4 Latin square with 5-wk periods. The pelleted hay had a marked effect in reducing the fat content of the milk. Ration C was most effective. When milk fat was decreased, SNF and protein increased. An average 33% decrease in milk fat was accompanied by a 5% increase in protein. The composition of milk was generally erratic while on Rations C and D. Milk production was not influenced by decreases in milk fat synthesis. The pellets were generally less palatable than long hay. Analyses of rumen volatile acids showed a relative decrease in acetic and an increase in propionic acids corresponding to the decrease in milk fat per cent. Concentrations of both acids were increased as compared to analyses when long hay was fed. Milk fat composition was markedly affected by Rations C and D. Iodine values were negatively correlated with fat content of the milk and values up to 61 were observed. Analyses of constituent fatty acids showed a general decrease in saturated acids and an increase in unsaturated acids when milk fat was depressed. Susceptibility to oxidized flavor did not appear to be correlated with the changes in milk fat composition.