^{From MCPE-113614:}
When you give a horse the health boost effect, the extra hearts are not shown when riding even though the effect is applied and increases the horse's hearts.

Steps to Reproduce:

(1)

• Generate two horses.
• Use commands to apply the health boost effect to them. 
• Mount them. 

(2)

• Use healing potions on one of the horses.
• Hit both horses doing the same damage to both. 

Observed Results:

(1) The extra hearts given by the effect will not be visible.

(2) The health of the horse that was thrown healing potions was not reduced, while that of the other horse was. Proving this, the health boost effect does apply as the healed horse reduced its health from extra (invisible) hearts.

Expected Results:

The extra hearts should be visible.

Original Description:
If you impose the effect on a horse: "health_boost" level 45, the horse does not display a large number of health units, but shows the amount that the horse had before this effect was applied, but the effect of the potion works.