The pregnant mare who was shot as she was about to foal.
Since 2007, the bodies of 13 wild horses have been found at various locations in the Rocky Mountain foothills west of Sundre.
Although not all could be confirmed as a result of a shooting, several had evidence that a firearm had been involved.
The Sundre Royal Canadian Mounted Police have announced the arrest of two adult males and one male youth in relation to one of the deaths, which occurred between May 2009 and October 2009.
Charges have been laid against Jason Nixon, 29, Earl Anderson, 40, and a 13-year-old youth who cannot be named because of Canada's Youth Criminal Justice Act.
Sergeant Patrick Webb told Horsetalk that all three are from the Sundre area and have been charged with willfully killing cattle. Under the Criminal Code of Canada, horses are defined as cattle for the purposes of the statue.
They have also been charged with use of a firearm in a careless manner.
Charges are pending on a 35-year-old male from the Calgary area, he said.
The charges are the result of a joint investigation involving the Sundre and Didsbury police departments, the local police division's livestock section, as well as Alberta Sustainable Resource Development fish and wildlife officers.
Nixon has also been charged with common assault on a person who was a witness to the Wildlife infractions. He has also been charged with uttering threats of bodily harm to a fish and wildlife officer and wilfully obstructing a fish and wildlife officer.
These charges stem from an incident which occurred on January 4, 2010 while the Fish and Wildlife officer was conducting his investigation into a trespassing and poaching complaint.
All three accused were released before a justice of the peace and their first court appearance has been set for March 1 at Didsbury Provincial Court House.
Sergeant Webb said inquiries into the horse shootings were continuing and he expected more arrests would follow.
He said the area in which the horses had been shot was rugged, heavily treed and remote in parts.
Police could not establish the causes of death in all cases, but in some bullets were recovered from the scene or bullet wounds were identified on the bodies.
"We are still inquiring into the deaths of the others. We anticipate we are going to be able to resolve some of the other cases."
Wild Horses of Alberta, a society pushing for better protections for the horses, welcomed the arrests.
"However, there have been 30 horses shot since 2002 that were either found by members or reported to us by members of the public, and subsequently reported to the police and the media," the society noted on its blog.
"The police continue to investigate those cases as well.
"This has been the day that we have been waiting for, for several years now, and have had many, many, moments of despair that none of the shootings would ever be solved. Perhaps this case is only the tip of the iceberg, we will just have to wait and see."