There are many types of hay in the market.
Mine are feeding fully on APD Gold but I do feed them Kaytee sometimes.
1) Get from reliable source - they replenish their stocks regularly
2) Keep your hay in cool and dry area
3) Avoid "yellow" coloured or moldy hay
4) Not all hay brand are the same. Different hays are only suitable for different animals
5) Feed more hay to your animal. Good for their digestive system