The effects of state government regulation of primary industry are modelled. An analytical framework is presented for estimating the costs of regulation in terms of changes in economic surplus. The model permits trade between regions of the total market. An illustrative application of the framework is applied to proposed animal welfare regulation of the Victorian pig industry. Some regulations that may provide large gains with regard to the welfare of farm animals involve only small social costs compared to the gross value of production of the industry. Conversely, other regulations that potentially confer only small gains in animal welfare impose large social costs. The distribution of these costs is important. In general, consumers lose, as do some producers. Other producers gain. In some cases, producers in aggregate gain from regulation. Major beneficiaries, such as advocates of animal welfare regulations, are likely to bear little of the cost of regulation.