Investigations with monozygous twin dairy heifers

Monozygous twins have been reported to have a higher value than non twins for experimental studies comparing two treatments, because these twins have no inherited differences. Differences which develop between identical twins are due to environment. Physiological processes such as growth and milk production are very complex and are regulated in some degree by more simple processes. Since monozygous twins are expected to react similarly in growth and production, they should also be expected to react similarly in less complex functions. Two physiological processes of particular interest in dairy cattle are the efficiency of feed utilization and the adaptability to high ambient temperatures. This investigation was planned to measure the differences in the physiological processes of monozygotic dairy heifers under the same environment and compare these differences with ones found within pairs of selected animals of the same age and weight. Growth of identical twin pairs fed at the same level and other pairs of identical twins at different levels of nutrition was measured. All data were compared to determine the value of Identical twins for experimental observations involving physiological processes.