Sleep is an essential behavior for mammals [1]. Many studies suggest the functions of sleep include energy conservation, nervous system recuperation, and emotional regulation [2]. Deep sleep occurs only when the animal is well-accustomed and feels safe in its surroundings [3], as the lack of muscle tone during sleep is innately dangerous for prey animals, such as cattle. Therefore, the sleeping posture (SP), that cattle adopt with their neck relaxed and their head against their flank whilst lying position [2,4], has been used as an indicator that the animal is relaxed and well-accustomed to its environment. Ninomiya and Sato [5] suggested that an enriched environment facilitates SP. Krohn and Munksgaard [6] suggested dairy cows in extensive environments (loose-housing/pasture) slept longer in the SP than when in intensive (tie-stall) environments. Lying posture (LP) has been also used as an indicator of a relaxed and well-acclimated animal [6–8]. Additionally, Oshio et al [7] suggested that daily total time and duration of bout of LP were important indicators of acclimation.

A change in the environment is a stressful event in livestock production. This includes major changes, such as introduction into a new herd after transportation, and minor changes, such as moving to a different stall in same shed. All changes in the environment disturb cow behavior to some extent, which requires several days to stabilize [7,8]. Understanding how cattle acclimatize to new environments could improve productivity and welfare [8]. Therefore, it is necessary to know how long cows take to stabilize SP and LP after moving to a new environment. The aim of this study was to examine the length of time taken for Japanese black cows to stabilize SP and LP after moving to a new environment. Furthermore, we compared between characteristics of SP and LP measurements.

This experiment was conducted at NARO Tohoku Agricultural Research Center in January and February 2016. The experimental procedure was approved by the Committee for Animal Experiments of NARO Tohoku Agricultural Research Center (No. 27–6).

The change in daily SP time after cows were moved to a new environment is shown in Figure 1a. Daily SP time on day 1 was 54.7±12.9 min/d (average±standard error), which was the shortest recorded in the experiment. Daily SP time increased to 83.0± 10.7 min/d on day 3, which was the longest recorded in the experiment, and then decreased until day 9. Thereafter, it fluctuated between 55 and 75 min/d. The change of the frequency of SP after cows were moved is shown in Figure 1b. Cows slept the least number of times on day 1 (7.6±1.9 times/d), but this increased on day 3 (13.6±1.4 times/d), and then decreased until day 9. Thereafter, frequency was about 10 times/d, except for a temporary increase on days 14 and 18. The change in average SP bouts after cows were moved is shown in Figure 1c. The longest SP bout was recorded on day 1 (7.48±0.44 min/bout), and bouts monotonically declined until day 7 (5.90±0.71 min/bout), and then remained stable thereafter.

The change in MSD of daily SP time is shown in Figure 2. The highest MSD was observed on day 1, and declined until day 7, except for a temporary increase on day 3. The results of the two regression models are shown in Table 1. The slopes of the first regression were negative, except for the breakpoint set on day 5. The total residual was the lowest on day 5, and the second lowest was on day 7.

The change in daily LP time, frequency of LP, and the average LP bout are shown in Figure 3a, 3b, and 3c. Daily LP time tended to change in the same way as daily SP time, reaching a stable level after day 7. The frequency of LP was relatively high from days 1 to 7, and stabilized to about 9 times/d after day 9. The average LP bout was the lowest on day 1 (62.0±8.9 min/bout). Thereafter, it increased and stabilized at around 105 min/bout after day 9.

In this study, total average daily SP time of pregnant Japanese black cows was 66.2 min/d, and ranged from 53.4 to 83.0 min/d. Norring et al [11] reported a similar dairy posture of lying with the neck muscle relaxed, which is equivalent posture to SP in this study (77±12 minutes in multiparous Finnish Ayrshires kept in a tie-stall). Krohn and Munksgaard [6] reported a shorter daily posture of lying with the head turned backwards, which is equivalent posture to SP in this study, (48±4 minutes in loose-housing, and 34±4 min in a tie-stall for monozygotic twins between Danish Friesian and Red Danish). Ninomiya and Sato [7] also reported a shorter daily SP time in Japanese black calves (ca. 20 min in a conventional pen and ca. 40 min in an enriched pen). Since there are many differences in experimental conditions between these studies, e.g., age, sex, breed, tethering, season, it is important to consider how different factors influence the daily SP time of cattle.

The change in daily SP time after cows were moved was too complex to observe using direct regression on the raw data. Therefore, we used the deviation between the observed and assumed stabilized levels, the average of which was calculated by shifting the start date from day 1 to day 18. The total residual was the lowest on day 5; however, the slope of the first regression was positive. This indicated that day 5 was not an appropriate inflection day because the intersection of both regression lines was out of range. Therefore, day 7, which showed the second lowest residual, was used as the appropriate inflection day for daily SP time. Oshio et al [7] reported that heifers and steers required about 1 month to stabilize grazing and rumination patterns after moving. Hasegawa et al [8] reported that behavioral disturbance after regrouping continued for 15 days. In this study, there was no influence of feed stuff, climate change, or social conflict as cows were tethered in a shed and fed the same stuff on almost the same schedule. Although the change in environment in this study was not as drastic as that in earlier studies [7,8], SP and LP were still disturbed by moving the cows, and they took 1 week to stabilize in their new environments. Therefore, attention should focus on cow behavior and posture within the first week after a minor disturbance, such as a change in location in a tie-stall shed, as disturbed cows might suffer a deterioration in productivity and welfare [8].

Both SP and LP have been used as indicators of relaxed and well-acclimated animals [3,5,6]. However, there are some differences between SP and LP. First, deviation of LP between cows in this study was adequate level although the age range of subjected cows was large. On the other hand, deviation of SP between cows was quite large. Therefore, we should use more subjects or consideration of experimental design for using SP as an indicator of cow’s relaxation. Second, the patterns of change were different between the average SP and LP bouts, even though the patterns of daily SP and LP time were similar. Cows spent the shortest time in SP on day 1; however, the average SP bout was the longest. Conversely, both daily LP time and the average LP bout were the shortest on day 1. The average SP bout gradually decreased, and reached a stable level after day 7, while the average LP bout gradually increased, and reached a stable level after day 9. Oshio et al [7] suggested that the duration of grazing and rumination bouts increased as heifers and steers acclimatized to a new grazing environment. Our results supported only the change in average LP bout, but not average SP bout. Krohn and Munksgaard [6] reported that cows laid for longer and slept for a shorter amount of time in tie-stalls, and vice-versa in loose-housing. These results imply a complementary relationship between LP and SP bouts.

SP-related measurements stabilized over 1 week, even after a relatively small change in environment. Careful attention should focus on the complementary relationship between lying and sleeping bouts when these postures are used as behavioral indicators of relaxation or acclimation.