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Milk yield data from herds at the University of Illinois and the University of Wisconsin-Madison were used to characterize milk yield fluctuations concurrent with conception. Analyses were performed on 118 Illinois and 244 Wisconsin cows; milk yields were recorded for 15 d preceding confirmed conception. Conception was confirmed by calving within 11 d of 281 d postbreeding. Each cow's difference between 7-d rolling means for a.m. and p.m. milking yield was subtracted from a.m. yields as a diurnal adjustment. A pattern matching formula that was applied to adjusted yields [( b - a]/a, where a and b were sequential milkings) produced a mean calculated value for the milking nearest conception that was different from all milkings for 15 d preceding conception in Wisconsin data only. Discriminant analysis failed to differentiate between preceding and conception inclusive sequences of adjusted milk yields. Pattern matching formulas applied to individual cow data failed to isolate more than 2% of conceptions when the threshold value was set to eliminate false positives. Results demonstrated low predictive ability for conception using concurrent milk yield fluctuations despite implications of significant mean differences for values that were enhanced by pattern matching formulas.