Speaking from experience Jill--my Konk for horses, which costs $8.95 per can, and which does repel mosquitoes, will spray less than half my herd. If I wanted to use it on everyone it would take me over 2 cans per application, probably more like 2 1/2 cans. It would be effective for 3 hours, tops. I've tried it, and in 3 hours the horses were covered in mosquitoes again.
Muskol--the 200g can which I can purchase in Wal-Mart for $5.97--I can spray everyone with 1 1/2 cans at most, and the horses get relief for just about the 8 hours that it says on the can. I spray in the evening as soon as the mosquitoes come out in full force, and it keeps the horses comfortable all night.
There is simply nothing as effective for mosquitoes as DEET, and the made for horses sprays (nor made for cattle sprays for that matter) are as economical as Muskol.
Word of warning on buying any bug spray labelled for cattle, even some of the products which are also labelled for horses--some of these products contain petroleum products and must be applied very sparingly. Using them too heavy or too often can cause skin burns on horses.
Wipe is one of more effective made for horses preparations. I don't know about down in the US, but here it's also the most expensive product--and I've still not found it to be as effective for mosquitoes as Muskol.
smudges...we have close neighbors so most times cannot build smudges, they tend to prefer mosquitoes to smoke! We do have some horses that absolutely love a good smudge--they'll go & stand right over the smudge, in the smoke. A few like to go & tear apart the smudge, and end up with singed fetlocks & tails--we try to build smudges in areas where the horses aren't, but that's not always possible. Many people put round bale feeders around the fire to keep horses out of it. Sadly I know someone who had a big horse yearling get through the feeder into the fire--she got half way through (presumeably she had her head through & another horse got after her & she lunged forward) and was stuck. When the owner found her she was very badly burned, still alive but in shock, and he had to destroy her. Truly an awful thing for that poor filly. So please, anyone building smudges, be very very careful and don't assume that using a round bale feeder makes it safe for the horses!