Technical Abstract: The lying times of lactating Holstein-Friesian cows of varying body condition scores (BCS) and milk yield were measured using IceTag™ animal activity monitors in the Barony College dairy herd. A three-week average BCS was calculated for each cow; and in total 84 cows were selected equally between 3 BCS categories (Thin: BCS < 2.75; Moderate: 2.75 ' BCS < 3.25; Heavy: BCS ' 3.25) and 2 stage of lactation categories (LCAT, < or > 150 days in milk). The cows were kept in two management systems: parlor/freestall (n = 24) or automated milking system/freestall (n=60). Behavior was recorded for 5-7 days for each cow. Production levels were considered using a 28-day rolling average of daily milk production. Cows that exhibited clinical lameness before or during the observation period were excluded from analysis. For cows exhibiting estrus, the day prior to, day of, and day following breeding were removed. The final analysis included 77 cows (421 days of observation). The effects of day within week, week, rolling daily average milk production, and days in milk category were included in a mixed model describing daily hours lying. Lying time decreased with increasing milk yield. Cows in early lactation spent significantly less time lying than those in late lactation. Variables that were tested but not significant (P > 0.05) were BCS category, management system, parity, age, pregnancy status, leg, tag, and herd of origin. After accounting for stage of lactation and production level, BCS did not significantly impact lying time. Management system, day within week, and week had a significant impact on number of lying bouts. Lying time is impacted by a number of management factors. Continued investigation of these factors using new technologies, more cows, and more herds will help dairy owners better manage facilities and cow movements to optimize this essential behavior.