Study by Wendy Pearson
In this work horses were treated with either a commercial single dose magnesium based calmer, a single dose of Acepromazine (veterinary sedative) or a placebo. The horses were selected because of their issues completing specific tasks and the impact on these tasks was evaluated. These are the characteristics sought by riders from a calmer.
Physiological effects were also measured in the form of average and maximum heart rates and blood cortisol levels.
Neither the magnesium nor the sedative affected the initial heart rates of the horses but both Acepromazine and magnesium depressed average heart rate in the horses completing the first task (loading onto an equine weighbridge). Despite that there was no significant improvement in the performance of the task suggesting that sedated horses are no better at this than unsedated ones.
As for the other 4 tasks (loading onto a trailer, travelling for 25 minutes in the trailer, having a blood sample taken from the jugular vein and spending 10 minutes in a stable with a strange object) there were no statistical differences between either of the treatments and the control group either in their performance of the tasks or their heart rates.
Blood cortisol was also measured. This is a hormone released during stress. The level increased in all three groups during the tests but there was no statistical difference between the control group and the Acepromazine or magnesium treatment groups.
All-in-all this experiment shows no significant calming effect (that horse handlers might want to see) from either veterinary sedation or from magnesium.
Tragically the firm that supported this research has this paragraph on their web site about this research:
“Consistent with their mandate of research behind their products, Xxxxxx Xxxxxxxx has published a new research study which demonstrates the effectiveness of this product in horses with anxiety issues.”
Wendy’s research is also in the Journal of Equine Veterinary Science 51 (2017) 86-91.