Curious, given that you are located in the NE where quality hay is grown and should be plentiful. Especially this time of year. Why would you feed “bagged hay” at $15 a bale?
There is nothing special about this stuff from what I can see on the label,
"Dehydrated chopped timothy hay, oat hay, alfalfa hay, cane molasses, propionic acid (preservative).
All hay is “Dehydrated”. The label doesn’t give a percentage of each “type”.
I grow and bale excellent Orchard with 1/3 Timothy, First cutting 40+lb bales I am selling right now for $6. Second cutting $7.
As to your question, I would check the bag before buying/opening and make sure it does not have a hole in it. Given the fact you are located in a high humidity area the very dry hay, (the manufacturer does not give moisture level) can and will suck in some, a lot of moisture. It is in a plastic bag and cannot “natural wick out”, breathe so the moisture can and will collect over time heat up and provide a breeding ground for mold.
If the bag is not compromised and the hay after opening is being “stored” in the bag it might be better once opened to take it out of the bag.
Per the label the hay is baled/processed with propionic acid basically a salt. Pretty much SOP with all hay producers in high humidity baling areas. Some horse will become disinterred with the “salty” taste after a while. The cane molasses maybe added to keep their interest and to keep the extremely dry processed hay from crumbling and turning into flakey “dust”.
We use Silo King Hay preservative, a dry granular “natural” preservative that is dropped/spread on the hay as it enters the baling chamber instead of being sprayed like propionic acid. I am told some hay producers also add green food coloring to the water based “acid mix” to gives the hay a bright green color. Both work well but Silo King has little to no residual “flavor” or smell.
Producers cannot “push” baling moisture levels as high with Silo King as they can with propionic acid.
We are located in a high humidity area bale and put up around 200 tons a year. We rarely find bad bales. The hay is just as good in looks and smell come late spring the following year as it was when baled.
Smell is not always indicative of the quality and or if the bale is good or not. What we like to smell isn’t always the same as what a horse likes to smell.
If the flakes in a bale are “caked” tight, with little to no smell, or a slightly "off "smell, but more importantly give off white “mold dust” when patted the hay is not good.
I have never used “bagged” hay. I would assume that after being processed it is compressed pretty tight so the above “caked tight” may not apply. And the fact I have never used it I am guessing as to why it is going bad on you. But my “guess” is based on making a lot of hay over the years. Good and bad.