Quoting from the Marilyn Manson site,
January 13, 1994- The Chicken Incident, Dallas Texas. Manson knocked a caged chicken around the stage, and tossed it into the mosh pit. Although rumors claim that the chicken was killed, it actually escaped relatively unharmed.
This story is also repeated in a different version in Letters to the Met by Karen Davis in an American Online interview transcript in 1995 with Marilyn Manson.
"Several eyewitnesses claim to have attended a [Dallas] rock concert featuring the band Marilyn Manson on January 13... during which time a band member kicked a live chicken as part of the performance and then threw the bird out to the audience. Reportedly, members of the audience dismembered the live chicken in a bacchanalian orgy of violence. "Karen Davis, President, United Poultry Concerns, Inc. Potomac, Maryland." (from Letters to the Met, Dallas TX.)
- Was there a chicken at a Marilyn Manson concert?-Yes, per Dallas TX publication The Met, the Ft. Lauderdale-based band Marilyn Manson used plenty of shock props in its live act brought a chicken to its Friday, January 13, 1994 concert at Trees.
"From what information we have pieced together on this incident, the Ft. Lauderdale-based band Marilyn Manson, which uses plenty of shock props in its live act, brought a chicken to its Friday, January 13  concert at Trees. ...Apparently, about halfway through the show, Mr. Manson (that's what you're supposed to call him), went to a cage where the chicken was being kept, opened it, and said something to the effect of, "Be free."
2. Was it injured or killed?-No The crowd nor Marilyn Manson band including Marilyn Manson did not slaughter the chicken with their bare hands.
"What happened next differs depending on whom you talk to, but we're pretty sure we know which version is true. A chef at a local restaurant saw the chicken and told a friend, "Catch that and I'll cook it." The friend obliged and chased the chicken through the mosh pit which had formed in front of the stage. He caught the chicken and was then approached by another member of the audience, who pleaded for the chicken's life and actually started pulling it away. We figure that in the confusion of chasing the chicken through the mosh pit, and the tug of war that cost the chicken some feathers, many concertgoers, specifically those who were not in the pit, may have thought the chicken was being torn apart. In fact, the chef's friend lost the tug of war, and the chicken was taken away. Whether the band got it back or not, we're not certain. But we know, at least, that a rabid crowd did not slaughter the chicken with their bare hands.
- Was it by Marilyn Manson?-No, referring to Dallas TX publication The Met. Marilyn Manson did not kill the chicken onstage.
"The chicken, which was requested on the band's rider (as a joke), was given to the band by the promoter of the Houston show prior to the Dallas date. She was not seriously harmed during the Dallas incident and is living on a farm outside of Dallas under the pseudonym "Foghorn".
- Was it an accidental or deliberate death?-No The chicken was quoted to be living on on a farm outside of Dallas under the pseudonym "Foghorn".
A chicken, requested as a joke by the band on their tour rider, was provided by the club's management, and taken on stage in a cage which it promptly escaped from during the band's set. It was rescued by fans, but United Poultry Concerns, along with many others, decided to take the incident very seriously, hysterically announced that 'the audience dismembered the live chicken in a bacchanalian orgy of violence'. Thus began the accusations of animal abuse that are often leveled at Manson, and, more humorously, the rallying cry 'Kill the Chicken!'
- Marilyn Manson also does not slaughter puppies as part of his stage show.