Laminitis is often a sequel to a disease or condition which in some cases triggers laminitis. 

All the listed conditions below are known to induce laminitis.

• Excess of carbohydrates (accidental access grain or over feeding)
• Obesity (lush pasture)
• Enteritis
• Colitis
• Peritonitis
• Metritis & retained placenta
• Azoturia

Generally the duration of the developmental phase is considered to last just a few days or hours at most, as a rule the triggering event will cause laminitis in a very short time. When the triggering event is unknown as in obesity induced laminitis, it's impossible to define the duration of the developmental phase, which in these cases can be months. 

The DWLT model of laminitis proposes that the systemic diseases which are associated with laminitis are not acting directly on the sensitive laminae but cause the heels of the hoof capsule to grow faster than normal. The laminae and other sensitive structures are then traumatised as the hoof capsule distorts beyond normal limits. The speed of heel growth, the shape and strength of the hoof will determine the duration of the developmental phase and the severity of the subsequent laminitis.

Despite encountering what could be a triggering event or being obese, not all equines become laminitic, one possible reason is that weak hoof capsules with flaring or dissipating heels will harmlessly splay outwards when the heels start to grow faster (Fig 1) and not cause the hoof capsule to distort at the toe. Another reason may be that rapid heel growth is not always initiated in some cases.

Generally, stronger hoof capsules are intolerant to rapid heel growth and become severely laminitic while weak flaring hooves don't distort at the toe so the laminae are not traumatised.

Fig 1. This hoof is showing signs of faster heel growth, fortunately for the pony the heels are splaying outwards and not causing distortion at the toe.