*4.4. Influence of Government Regulation on Farmer's Behavioral Choices*

Regulative tactics can influence antibiotic use in different ways [28]. Hence, in our simulation experiments, government regulation of pig farmers' VA use was reflected by spot checks and penalties for improper use. The experimental results are shown in Figure 5, which illustrates the relationships between government regulation (in terms of different numbers of random checking and amount of penalty) and farmers' VAs use. When the sampling rate in spot checks and the penalties were both low, the proportion of farmers with improper VA use (approximately 80%) was much larger than that with proper use (approximately 20%). When the sampling rate in spot checks increased, the proportion of farmers with proper VA use (fluctuating between 50% and 60%) was slightly higher than that with improper use. Furthermore, when the penalties were increased, the number of farmers with proper VA use was significantly higher than that with improper use. This was consistent with the findings of Chen et al. [29] on the behaviors of pig farmers.

**Figure 5.** Simulation results of the changes of farmers' behavioral choices regarding VA use under the variation of government regulation: (**a**) the probability of the farmers' improper VA use checked by government regulators was set to 0.3 (*q* = 0.3), and the penalty for improper VA use was set to 30,000 yuan (*C*<sup>1</sup> = 3); (**b**) *q* = 0.4, *C*<sup>1</sup> = 3; (**c**) *q* = 0.4, *C*<sup>1</sup> = 4.
