Probiotics to prevent illness

Looking for recommendation of a suitable probiotic to give the 6 dogs before their trip to the Kennels. The only times that they have been away they have all come back with D&V, one so bad that he ended up at the Vets on an IV for 3 days.
This time its a new Kennel with no reports of illness in dogs after they have left.
More likely to be stressed induced so hope there is something available for them

Probiotics are bacteria or yeast really for aiding the digestion processes, there are claims for immune boosting, but this is long term benefits.
Instead I would supplement with vitamin C for 2 weeks before the kennels (or as soon as) which helps with stress (thus boosting immune system in short term). Try to get raw without sugar or sweetners - health food shop is your best bet.... look for 'ascorbic acid'.
For dachys I would put in a pinch in every bowl. (Mine would get half a tea spoon) but you can't over supplement, it is soluble and comes out in the urine.