outdoor pig keeping system

例句：

1. 1.The outdoor pig keeping system is an effective way to control the pig population.
   户外养猪系统是一种有效的控制猪群数量的方法。
2. 2.The outdoor pig keeping system helps to reduce the environmental pollution caused by livestock farming.
   户外养猪系统有助于减少畜牧业造成的环境污染。
3. 3.The outdoor pig keeping system has been widely used in rural areas, providing a convenient and efficient way for farmers to raise pigs.
   户外养猪系统在农村地区得到了广泛应用，为农民提供了一种方便、高效的养猪方式。