Exploring synchrony of lying on commercial dairy farms in relation to management

Synchronous lying may be an indicator of positive welfare in dairy cows. However, little is known about whether farms differ in the level of lying synchrony and how consistent this is within a farm. Moreover, the level of synchrony may vary within the day. Accelerometers used for estrus detection of cows enable continuous monitoring of synchronous lying of herds. We studied the level, timing and duration of synchronous lying in 8 Holstein Friesian or Holstein dairy herds across 1 year, in relation to grazing and milking management (robotic milking, 2x and 3x daily milking). In ‘winter’ months (November-March), herds were housed; in ‘summer’ months (May-September), 6 of 8 herds had access to pasture for 5–8 h per day, the other 2 herds were full-time housed. April and October were excluded because of variable management. Herds had 0.9–1.4 cubicles available per cow. After cleaning individual accelerometer data, herd average lying time was computed per 15-min (900 s) interval. An interval was defined as synchronous lying when the herd average lying time > 540 or > 630 s (i.e. assuming 60% or 70% of the herd was lying). Daily synchronous lying time was defined as the number of synchronous intervals × 15 min. A general linear model was used to assess effects of farm, season, and their interaction on synchronous lying time per day; with Tukey-adjusted pairwise comparisons. Correlations were made per farm per season to assess the association between total daily lying time and synchronous lying time. Across all herds and calendar days, the highest level of synchrony reached was on average 78%. Most synchronous lying occurred between 2AM and 6AM, though this was not true for all farms. Synchronous lying occurred least between 4 and 8 PM. Across farms, average synchronous (60% threshold) lying time per day was 5.9 h in summer (range: 2.7 – 7.9 h) and 5.5 h in winter (range: 1.6 – 9.1 h). In 3 out of 6 farms with grazing, synchronous lying time was higher in summer due to occ