What does Horse Strength do?

Based on the information collected in this Reddit thread, it appears that the Strength stat of a horse does, indeed, affect how much HP it has.

Don't ask how the science was done. :'/

• 1 star ~ 60hp or two hits with a lvl 30 weapon
• 2 star ~ 120hp or four hits with a lvl 30 weapon
• 3 star ~ 180 hp or six hits with a lvl 30 weapon
• 4 star ~ 240hp or eight hits with a lvl 30 weapon
• 5 star ~ 300hp or ten hits with a lvl 30 weapon

Boarding your horse resets the strength as does taking it out from another stable. Hope this helps.

Note: Only 2, 4, and 5 star strength horses were used in this study. 1 and 3 stars were extrapolated using complex mathematical models.