Sampling cows to assess lying time for on-farm animal welfare assessment

The time that dairy cows spend lying down is an important measure of their welfare, and data loggers can be used to automatically monitor lying time on commercial farms. To determine how the number of days of sampling, parity, stage of lactation, and production level affect lying time, electronic data loggers were used to record lying time for 10 d consecutively, at 3 stages of lactation [early: when cows were at 10-40 d in milk (DIM), mid: 100-140 DIM, late: 200-240 DIM] of 96 Holstein cows in tiestalls (TS) and 127 in freestalls (FS). We calculated daily duration of lying, bout frequency, and mean bout duration. We observed complex interactions between parity and stage of lactation, which differed somewhat between tiestalls and freestalls. First-parity cows had higher bout frequency and shorter lying bouts than older cows but bout frequency decreased and mean bout duration increased as DIM increased. We found that individual cows were not consistent in time spent lying between early and mid lactation (Pearson coefficient, TS: r = 0.1, FS: r = 0.2), whereas cows seemed to be more consistent in time spent lying between mid and late lactation (TS: r = 0.7, FS: r = 0.3). For both TS and FS cows, daily milk production was significantly, but slightly negatively, correlated with lying time across the lactation (range, r: -0.2 to -0.4), whereas parity was slightly to moderately positively correlated with mean bout duration across the lactation (r: +0.2 to +0.6) and negatively with bout frequency (r: -0.2 to -0.5). To estimate how the duration of the time sample affected the estimates of lying time subsets of data subsets consisting of 1, 2, 3, 4, 5, 6, 7, 8, and 9 d per cow were created, and the relationship between the overall mean (based on 10 d) and the mean of each subset was tested by regression. For both TS and FS, lying time based on 4 d of sampling provided good estimates of the average 10-d estimate (90% of accuracy). Automated monitoring of lying time has potential as a measure of dairy cow welfare on commercial farms but cows differ greatly in lying time. To obtain a representative measure for the herd, it is necessary to sample cows based on their parity and stage of lactation but probably not milk production level.