A guinea pig will appreciate some bedding material in which to "nest" and this is best provided with a deep layer of wood shavings and large amounts of hay.
Any hay given should be clean and free from dust or mould as the guinea pig will eat the hay as well as use it for a bed (see Feeding) and this is vital for their digestive system. Therefore hay needs to be topped up daily.
Timothy hay or a grass hay is best given although alfalfa hay can be given to young growing guinea pigs and also to pregnant and nursing mothers. However, alfalfa hay is considered too high in calcium for continued use throughout adulthood although can be given as an occasional treat.
Straw should not be used as the sharp edges can injure a guinea pig eyes. | 
