Animals did not sin, they have done nothing wrong.
You raise some outstanding points. In the same way, though, infants have done nothing wrong, nor have they sinned. One can argue that they learn nothing from their suffering and that's a valid point as well, but in the end we simply don't know what people or animals gain from life on Earth. My own personal belief is that in the beginning, a plan was formed, we agreed to it, the Earth was created, man fell purposely because he could not attain to the glory of God in the state he was placed in the Garden. This is something the Orthodox Church has repeatedly addressed. In short, as Father Kallistos Ware stated in his book, The Orthodox Way, "[God] became what we are, so as to make us what he is." (Page 97) He asks, "Should we look behind the fall and see God's act of becoming man as the fulfillment of man's true destiny?" And he states, "The Incarnation, then, is not simply a way of undoing the effects of original sin, but it is an essential stage upon man's journey from the divine image to the divine likeness." And while the Jehovah's Witnesses say only 144,000 receive this potential, other religions don't buy it.
They do not benefit or learn from their suffering and death in any way, do they?
We don't know, but if God is just and merciful, I'd say yes, absolutely. Not everything has been revealed, but as you noted, what a horrible injustice it would be be to create animals, make them suffer and require their very existence from them, then treat them as non-entitities, never to be seen or heard from again. Wouldn't it make more sense to create them as artificial intelligence, to mimic pain, suffering, love, affection and so forth? That way they wouldn't suffer at all. We would simply think they had suffered. Of course I don't believe that at all, but it would be better to do that than to make these creatures actual sentient beings, cause them pain, untold suffering, give them awareness and then discard them. How would this make God any less of a monster than ISIS? (A captured Jordanian pilot is put in a cage and burned to death by terrorists. But many Christians who condemned ISIS for this horrible deed had no trouble believing that this unfortunate Muslim pilot just kept right on burning in Hell because he was not a Christian. If true, God would be more of a monster than ISIS because his suffering would be eternal.)
You admit they experience emotions, and yet they don't have the intelligence that we do to read a holy book and find comfort and understanding of why they suffer, as many people do from their beliefs.
Yes, but there are many people who lack that same ability. We also don't need to understand these things in our own lives, either, because we either don't understand or believe our own holy books. Most of my own beliefs in this matter don't come from the Bible but from other scriptures you don't believe in. Some here don't believe in any holy book at all, but believe that all suffering is horrible and meaningless -- and that if there is a God, then He is heartless and a monster.
For years I've suffered from a bicycle accident that happened back in 2001. Every day I'm on painkillers, but I worked for NIH at the time, so I knew a lot of doctors. One day I asked one of them at the Pain and Palliative Care unit how people back in the 1800s dealt with such issues. He didn't say a word. He just turned his hand into a mug and tipped up to his lips as though drinking. Then he turned the mug into a pistol and pointed his finger at his temple and clicked his thumb. So personally I have to think there's a reason for suffering or there would be no reason for me to live. But I wouldn't needlessly addict suffering on any person or animal if I didn't think there was a purpose. If I did it, I would be a monster. And if God did it, He would be a monster. But I don't believe God is a monster.
They cannot even ask for help when they need it.
Not true. Most people with pets, most farmers with cattle, know animals can ask for help. My cat got very sick last year and I could tell by the way he acted and sounded that he was in pain and distress. This was reinforced when I brought up his cat carrier and he got right into it instead of heading in the opposite direction. He knows the carrier is for vet visits and, somehow, that it has something to do with his health. He came close to dying, but they saved him. Now the cat wants no part of the carrier.
Their suffering is unjustifiable.
But is that for us to decide? Either God exists or He doesn't. If He doesn't, man is simply engaging in polemics. If one is a Christian, one usually concedes that man doesn't have the whole picture -- that God has a more complete understanding than man. If religion is a sham, then man has the only picture, in which case not only is the pain and suffering of animals cruel and meaningless, the pain and suffering of all living creatures is cruel and meaningless. And if they're correct about there being no God, it becomes a situation of our not being able to do anything about it.