I NEVER use oat straw around chickens! I've learned that oat straw can cause an impacted crop in chickens. The chickens peck at the straw and eat it. It cannot be easily digested and the crop gets a hard ball of straw inside. This keeps other food from digesting correctly. If the ball of straw gets too large, the chicken can die. I've had it happen and seen it happen to others. Best to use some other bedding.
A wonderful alternative is alfalfa hay! This can be used as bedding for newborn chicks and they will not get "pasted up" and will receive the benefits of the extra protein. Try to get organic alfalfa hay for chicks. It's also a great lining for nest boxes - keeps eggs clean and safe. Chickens LOVE to eat the small leaves of alfalfa hay. It also makes dark yellow and even orange yolks as the beta-carotene in the alfalfa passes into the egg.