## 3 Results
### Pig Behaviors from Direct Visual Observation  
#### 3.2.1 Circadian Rhythms in Pig Behaviors  
Sows and piglets showed more variation in their circadian rhythms in some behaviors compared with others. Additionally, their active times for different behaviors varied throughout the 24 h period (Figures 3 and 4). The sows showed two distinct periods of activity during the day and night, specifically for eating, standing, and drinking. These active periods typically occurred from early morning (around 05:00) to noon and from late afternoon (approximately 16:00) to 22:00 at night. However, the eating behavior of sows under cooling conditions did not display as pronounced a pattern as that of the heat stress-treated sows. Sows under natural heat stress showed less eating behavior from 13:00 to 17:00 but had more eating behavior from 21:00 to 23:00 than those under cooling treatment. Among the four observed behaviors of sows on-feet, only the sitting times were distributed quite evenly over the 24 h period.  
Regarding the sow on-body behaviors, lying times were predominantly in the morning from about 06:00 to noon and in the afternoon approximately from 15:00 to 21:00, with fewer sows lying in the afternoon. The sows tended to nurse more from around 18:00 in the evening to about 6:00 in the morning the next day. Sleeping times for the sows were mainly from late night around 21:00 to early morning around 05:00, with a peak number of sows sleeping in the afternoon between 13:00 and 14:00.  
\begin{table}
\begin{tabular}{c c c c} \hline  & **Visual Observation** & **Sensor Detection** & **Video Recording** \\ \hline Behavior distinction & Yes & No & Yes \\ Equipment requirement & No & Yes & Yes \\ Data collection method & Human observation & Sensor detection & Video shooting \\ Data collection mode & Discrete & Continuous & Continuous \\ Data collection frequency & Every 5 mins & 1 Hz & 20 frames per sec \\ Data recording & Notepad & Computer & Computer \\ Data type & Binary data & Analog data & Sequence of images \\ Response time & A couple of secs & \(\sim\)1 s & \(<\)1 s \\ Researcher involvement & High & Low & Low \\ Invasiveness & Possible & No & No \\ Data storage requirement & Low & Medium & High \\ Data processing requirement & High & Low & High \\ \hline \end{tabular}
\end{table}
Table 2: Comparison of three methods for sow and piglet behavior study.  
The study revealed interesting correlations between the piglet walking times and the sow lying time, evidenced by moderate correlation coefficients (\(\rho\)) of 0.425 and 0.416 for the heat stress and cooling treatments, respectively. A strong positive correlation was observed between piglet nursing times and sow nursing times, with \(\rho=0.853\) for the heat stress and \(\rho=0.671\) for the cooling treatments. These correlations likely reflect the close bond between sows and their piglets. It was also noted that piglet sleeping times were more uniformly distributed throughout the day, except for their walking periods.  
Figure 3: Visually observed numbers of pens where sows were eating, drinking, standing, and sitting at different times of the day under heat stress (charts with red curves) and cooling (charts with blue curves) compared with room temperature (bottom left) and relative humidity (bottom right) in the two rooms.