Post-test on MCMCglmm posteriors distribution

Dear all,

I have a quite simple question but I do not find a clear answer on the 
internet nor in books.

The context : I am currently working on different aspects of bird aging. I 
have done animal models with MCMCglmm to find if there is an additive genetic 
variance (Va) in my sexual life traits. One animal model has been done by age. 
Now, I am interested in testing the differences in Va (posterior mode) between 
ages.

My question : As posterior predictions are supposed to be normally distributed 
(if the model converge), is it possible to use multiple Student test 
(corrected for unequal variance and pairwise multiple comparison) to test 
statiscal difference on posterior prediction? It seems to me that all 
assumptions are meet to use Student test but maybe there some problems that I 
am not thinking about.

If you have a more elegant way to test differences of posterior distributions, 
let me know!

Thank in advance for reply and sorry for this beginner question.

Stephane