You can't "call a Cow", they way you would call a bull. Just doesn't work that way. Saying that, a cow that has lost here calf can usually be attracted by the sound of a calf in distress but only if she lost the calf within the last day, maybe two. She will stay in the general area, usually within a quarter mile.
If someone kills a calf moose and removes it from the area, Momma will come to "investigate" a distress call.
A little caution here too, Momma moose may not be in the best of mood either, she's comming to assist her young who is calling for help. She can get pretty bitchy and those hooves can be deadly.
Those calls are actual moose. Practice them. The better you get,the better the chance of success. Personaly, I prefer a birch bark horn, 18-22 inches long, it reverberates the sounds better.
Try to put your tree stand in a tree with plenty of background cover, keep the prevailing winds for that time of the year to your face, and take care of those pesky squeaks and creaks your stand may have developed while sitting in the shed. A good treestand lube can be made by heating petroleum jelly until it reaches a liquid form. Some hunters have reported success by including a cover scent in this mixture before applying it to their stands.