Per the Bible, the "fallen angels" are being held "in chains of darkness, reserved unto Judgment Day," which means they aren't around to cause trouble today as many suggest.  Judgment Day is a long ways away - the end of the world.  The fallen angels won't see the light of day until then and only long enough to be judged, per the following:

 

Jude 1:6 - "And the angels which kept not their first estate, but left their own habitation, He hath reserved into everlasting chains under darkness unto the Judgment of the Great Day."  [KJV]

 

2 Peter 2:4 - "For if God spared not the angels that sinned, but cast them into Hell, and delivered them into chains of darkness, to be reserved unto judgment," Vs. 9:  "The Lord knoweth how to deliver the godly out of temptations, and to reserve the unjust unto the day of judgment to be punished:" [KJV]

 

Some offer the alternative explanation that the "sons of God" mentioned in Genesis 6 were fallen angels who intermarried with women.  However, Jesus told His disciples that in Heaven we will be like the angels where there is no giving and taking in marriage.  This means the angels do not have seed for reproductive purposes.

 

How can we be sure?

 

God said the reason He made marriage between two people was for the purpose of producing a "godly seed."  [Malachi 2:15]  He never told angels to reproduce.  He only told Adam and Eve to "replenish the Earth."  That's because when Lucifer was cast down to Earth with 1/3rd of the fallen angels (between Genesis 1:1 and 1:2) he and the fallen angels went about destroying everything in a "hissy fit," for being cast down so fast, per God to Dr. Richard Eby during his 'life after death' experience.  That's why the Earth became "without form and void."  God had to recreate everything necessitating Adam and Eve to "replenish the Earth" with human life.

 

God said He changed Lucifer's name to "Satan" because Lucifer purposed in his heart to be a "self-appointed adversary to God" to go about destroying everything he could of God's creation thereafter.  ["Didn't You Read My Book?" by Dr. Richard Eby]

 

The Biblical definition of "heirs to salvation" is the "sons of God."  They needed salvation through Jesus' death on the cross due to being of the fallen seed of Adam and Eve.  "To those who believe on Him (Jesus,) He gives the power to become the sons of God.." [John 1:12]

 

Angels are not from the corrupted seed of Adam.  So angels are not "sons of God."  The good angels don't need saving.  The fallen angels can't be saved.  There is no in between.  Even the psalmist and Hebrews state that God never called angels His "son:"  "To which of the angels said He (God) at any time, 'thou art My son, this day have I begotten thee?'  [Hebrews 1:5 and 1:13]  In other words, God never called angels His sons and never will.

 

Plus, the angels weren't descendents of the giants because per Genesis 6:4, the giants were already here before the "sons of God" came:  "There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown."

 

One credible possibility is that Genesis 6:4 is referring to the "righteous sons of Adam and Eve," per an ancient book of Adam & Eve (Library of Congress) that states they lived on a mountain (possibly Mt. Hermon).  Adam warned his sons not to go down to the valley below where Cain -- who killed Abel -- lived with his descendants or they would become like them.  When Adam and Eve died, these righteous sons were lured down the mountain by the music, partying and beautiful women.  They ended up intermarrying with them, thus producing "men of reknown," apparently because they were a mix of righteous upbringing as opposed to Cain's sinful descendants and therefore, stood out..

 

Gino, you said, "fallen celestial beings are probably the ones perpetrating those horrific acts against cattle."  Psalms 33:6 says, "By the word of the Lord were the heavens (plural) made; and all the host of them by the breath of His mouth."  God created everything but mankind by speaking it into existence; i.e., "Let there be light.."  But man He created from the dust of the earth and "blew into his nostrils His breath of life and man became a living soul."

 

This means, therefore, that the first part of Psalms 33:6 is referring to inanimate objects that God spoke into existence, whereas the second half is referring to all the human/

human-like life God created that necessitated His blowing His breath of life into in order for them to become "living souls."

 

So, God did not fill the heavens with demons as many suggest (who believe aliens are demons) though there is a realm demons dwell in.  God filled the heavens (plural) with human/human-like life that have His "breath of life in them."  That means there is alien life throughout the heavens that God created.  Logic dictates that aliens can become demon-possessed, just like humans can, but it does not mean that all of them are, anymore than that all humans are.  So it isn't evil angels perpetrating those "evil acts against cattle."  Besides, what would angels need with cow parts?  It helps to know that there are good and bad aliens, just as there good and bad humans.