This study finds that the livestock environmental regulation (LER) imposed by China has promoted the spatial agglomeration of hog production in the administrative border areas, thereby posing a threat to ecological sustainability. We apply the difference-in-differences-in-differences (DDD) method to a unique dataset in counties along the main stem and 38 important tributaries of the Yangtze River basin in China from 2008 to 2019. Specifically, the slaughter volume and density of hogs in the most downstream border counties of a city are 7.87% and 9.56% higher, respectively, than those of otherwise identical counties within the same municipal jurisdiction. Conversely, in the most upstream border counties, these figures decreased by 12.02% and 15.35%, respectively. Moreover, we find that the fixed capital investment in the most downstream border counties is 22.54% less than that in otherwise identical counties. These findings imply that LER has driven the agglomeration of hog production in downstream administrative border areas, inadvertently shifting the pollution burden to these regions and posing potential challenges to the effectiveness of environmental policies.

Although environmental regulations are intended to improve ecological conditions, their implementation may also be accompanied by a relative concentration of polluting activities in boundary areas, thereby increasing pollution pressure in these locations. Hog production has long been a major contributor to water pollution in China. In response, the Chinese government has implemented the most stringent livestock and poultry environmental regulations (LERs) in its history. Using a staggered DDD model and a manually collected panel dataset covering 1028 counties across ten provinces, this study examines the effects of LERs on hog production and water pollution pressure in boundary counties. The findings show that LER implementation increased slaughter volume and slaughter density in boundary counties by 8.68% and 11.42%, respectively, with stronger effects in economically less-developed regions, consistent with the “pollution haven” hypothesis. The effects of LERs exhibit significant heterogeneity across different hog-farming functional areas, with notable increases in hog production in boundary counties located in potential growth and constrained development areas. The increase in hog-farming intensity in boundary areas is associated with modest increases in selected water-pollution indicators. Specifically, LERs weaken the positive relationship between hog production and water pollution to some extent, but the relative expansion of hog production in boundary areas following LER implementation remains associated with additional pollution pressure. After accounting for the mitigating effect of LERs, the marginal effects of slaughter volume on CODMn are 0.0672, and the marginal effects of slaughter density on CODMn and NH₃-N are 0.0916 and 0.0755, respectively. The findings offer policy-relevant insights for improving the effectiveness of environmental regulation and addressing boundary-pollution issues.