A computerized dairy herd simulation was developed to evaluate the economic impact of changing length of lactation relative to length of dry period in a dairy herd. It created weekly production for individual cows in a typical herd. Cows were dried off early if they were producing below a designated daily milk yield. They were replaced with fresh cows to produce more daily milk and increase profit while maintaining a constant number of cows in milk (98 to 102). A two by four factorial of dry off strategies was designed using rates of lactation decline of 6% and 8% and early dry off at 8, 13, 18, and 23 kg. Cows producing less than this for 2 wk consecutively were dried off. There were 100 cows in each herd and each of the eight scenarios was run 10 times (10 herds) for 80 herds total. Dry cow groups at 8, 13, 18, and 23 kg dry off were 14, 17, 23, and 32% of total herds, respectively. Average daily milk (kg) increased for the four dry kg: 30.4, 31.2, 32.3, and 33.7 kg/d per milking cow, whereas RHA decreased. Three different milk-feed income scenarios, (+20%, average, -20%) were combined with three dry cow costs, (+20%, average, and -20%). Nine combinations were analyzed statistically at each rate of decline. Net cash income changed $3561, $1571, and $-3051 from 8 to 13 to 18 to 23 kg dry kg under a normal economic situation. Net farm income under the same scenario changed $3170, $2945, and $-1154. Under the best economic situation, net cash income increased with each successive dry kg, $5086, $4248, and $921. Net farm income also increased by $4695, $5621, and $2819. Net cash income and net farm income were largest at 13 and 18 kg when milk-feed income was low and dry cow cost was high, the worst economy scenario. Only in the most optimistic economic situations does it appear practical for a dairy business to adopt early dry off beyond 13 kg/d per cow given the small gains and the yearly variability. Strategies of dry off at larger dry kg, although not greatly profitable, nevertheless were not extremely unprofitable either. / Master of Science