I use oxyclean! I let it soak for a while and with my saddle pad it makes a major difference! You can use bleach on your pad but not on your girth. try the oxyclean and spray it on the fleece part only, then wash it.
When I bought DD a new fleece girth for her pony I VOWED to wash it after EVERY ride! I have and it is still nice and fleecy white! they are not too bad to wash daily as they dry quickly under a ceiling fan on the back of a kitchen chair! Same with her show pad , it gets washed right away each time we use it!
If you are lucky enough to ride, you are lucky enough.
I use a borax, washing soda, and Mrs. Stuart's Blueing. Works great! If they are still not white enough I use a lot of bleach and then wash again with the aforementioned combination of ingredients before drying.