## 4 Discussion  
The ambient temperature inside a pig house is a crucial parameter for pig farming, and variation in this parameter may have a negative impact on pig productivity [17]. In Korea, heating pig houses is essential during the winter season, whereas they need to be cooled in hot weather. Research has shown that heat shock or cold stress substantially affect the growth and reproduction performance, welfare, and health of animals [18; 19]. In general, cold stress is common in weaning pigs, while the effects of heat stress are more of a concern in finishing pigs. Therefore, a major proportion of the total cost involved in pig farming is spent on maintaining the optimum temperature for pigs [20]. Similarly to our study, various experiments conducted in other countries have also reported the cooling and heating efficiencies of GHPs in broiler houses and swine farms [4; 15; 21]. In the current study, the decrease in temperature in the GHP-installed house might be because of the efficient degree change per unit of energy consumption of the GHP system [9]. Additionally, a direct heat exchange system in a single-loop configuration increases the efficiency of the GHP system [22], which can efficiently increase or decrease the temperature of the pig house depending on the season. THI is considered as a basis for the safety index to explain the categories of heat stress in animals. [PERSON] and [PERSON] [19] reported that humidity is not harmful for swine unless a high temperature is combined with a high humidity. According to the National Atmospheric and Oceanic Administration [23], THI \(\geq\) 84 is classified as an emergency, THI \(\leq\) 74 is safe, and 74 \(<\) THI \(<\) 79 is considered as an alert for animal welfare. In the present study, the THI of the GHP-connected pig house fell within the safety zone for all of the phases of growth. The COP is measured by dividing the heat output (kWh) by the electrical input (kWh), and it indicates the performance of the cooling system. The calculated COP-day average in this study was 4.36, with the COP ranging from 4.10 to 4.50. The calculated COP of the GHP cooling system was the same as the COP of 4.38 observed by [PERSON] et al. [9] for a GHP cooling system. On average, the COP of a ground-source GHP lies within the range \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Control** & **GHP** & **SEM** & \(p\) **Value** \\ \hline \multicolumn{5}{c}{0–5 weeks} \\ Initial body weight (kg) & 6.18 & 6.17 & 0.37 & 0.9910 \\ Final body weight (kg) & 23.74 & 25.84 & 0.88 & 0.1250 \\ Weight gain (kg) & 17.56 & 19.67 & 0.77 & 0.0850 \\ Feed intake (kg) & 26.60 b  & 31.10 a  & 1.26 & 0.0350 \\ Feed conversion ratio & 1.52 & 1.59 & 0.06 & 0.4390 \\ \multicolumn{5}{c}{6–9 weeks} \\ Final body weight (kg) & 48.53 & 51.35 & 1.66 & 0.2490 \\ Weight gain (kg) & 24.79 & 25.51 & 0.91 & 0.7250 \\ Feed intake (kg) & 51.83 b  & 52.71 a  & 2.21 & 0.0005 \\ Feed conversion ratio & 2.11 & 2.07 & 0.05 & 0.6700 \\ \multicolumn{5}{c}{10–14 weeks} \\ Final body weight (kg) & 75.61 b  & 82.58 a  & 1.88 & 0.0220 \\ Weight gain (kg) & 27.09 & 31.23 & 1.01 & 0.0840 \\ Feed intake (kg) & 81.29 b  & 91.62 a  & 2.42 & 0.0140 \\ Feed conversion ratio & 3.03 & 2.94 & 0.14 & 0.8210 \\ Final body weight (kg) & 108.47 b  & 15–19 weeks & \\ Final body weight (kg) & 108.47 b  & 118.17 a  & 2.56 & 0.0240 \\ Weight gain (kg) & 260.88 & 295.96 & 6.96 & 0.0780 \\ Feed conversion ratio & 2.56 & 2.64 & 0.05 & 0.4390 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Effect of the GHP cooling mode on the growth performance parameters. of 4.19 to 4.57 in cold weather and 3.9 to 4.53 in the summer season [24]. The results of the present study also fall within the optimum parameters, indicating the performance index and efficiency of the GHP cooling system. [PERSON] et al. [25] also reported that water-water-type GHP systems are popular in Korea because of their ability to heat and cool, and their better COP values.