Paddy is generally his favorite groomer, I think because they've known each other the longest. They'll stand shoulder-to-shoulder and go after all sorts of spots, generally for 15-20 minutes (unless I disturb them with my annoying picture-taking).
Geez, lady, we're busy here.
Griffy will also do if Paddy's busy. I've watched T push Griffy off the hay and then shove himself in front of Griffy's face, pretty much demanding to be groomed. T will sometimes nip Griffy on the leg - apparently he doesn't always do it right? - and then they'll switch sides or Griffy will groom a new spot. T is very clearly in charge of those interactions.
You must groom me now.
Right there is good.
Recently, we've been horse-sitting a spare Haffie, named Art. T and Art literally gave each other one "Hi My Name Is" sniff over a gate, and then started grooming. Geez, T, way to make an impression. Since then, they'll go at it any chance they get.
No T, we cannot keep this one even if he's an excellent grooming buddy.
I did a little digging about mutual grooming, but there doesn't seem to be a lot of scientific research out there. Apparently horses that groom each other are generally close in herd status, and do it to cement herd bonds. According to Kimura's (1998) study of free-ranging horses, aggressive-submissive behavior (i.e. T nipping Griffy) can sometimes be seen and used to determine herd status. However, mutual grooming is based on the bonds between individuals, not social rank. This is interesting because I've never EVER seen Reddums engage in grooming with anyone, even T, and Reddums has always been kind of a loner.
Sigurjonsdottir et al (2003) found that in a mixed herd without a stallion, rank was significantly correlated with age, which is true in our herd (but hasn't always been). Christensen et al (2002) found that young stallions who were boxed alone for 9 months tended to significantly increase the level of mutual grooming and play behavior when returned to a herd. The authors suggested this was a "rebound effect", and may be what I'm seeing with Taran since he was not turned out with other horses when at the trainer's.
I'll scratch your butt, you scratch mine.
What amazes me most about these grooming sessions is that somehow each horse knows where the other one wants to be groomed. There has apparently been some study of facial expressions to see if it's possible to determine how they communicate this, but so far nothing conclusive.
Has anyone studied why horses lick other horses? Because someone probably should, and I volunteer T as the number one subject of study.
Does your horse have a grooming buddy, or more than one? Do they try to groom you, or ask you to spend extra time on certain itchy spots when you're grooming?
Christensen et al, 2002. Effects of individual versus group stabling on social behaviour in domestic stallions.
Kimura, 1998. Mutual grooming and preferred associate relationships in a band of free-ranging horses
Sigurjonsdottir et al, 2003. Social relationships in a group of horses without a mature stallion