There are many things to consider when you have animals, such as enclosing their habit to managing their manure.
We have had numerous customers come in and explain that their animals were injured using softwood (big box store) rails. The went on further to explain that they bought treated materials that penetrated the skin and caused health problems to their animals.
The alternative is using hardwood rails. They are typically more expensive, but within the last few years, not as much. Softwood rails splinter on a break-through, which can injure your animal. Hardwoods are much stronger and typically do not fracture the way softwood does, minimizing the danger to your animals. Our hardwoods also do not contain preservatives, which are not needed for longevity as they are in softwood products from the big box stores.