The underlying issues
When we are talking about the issues of the horse's musculo-skeletal system, we tend to (quite literally) look at things a bit one-sided. We talk about poll issues, neck issues, back issues, and pelvic issues. We focus on the upper (dorsal) aspect of the horse's body and generally pay no attention to the lower (ventral) side. But the belly matters too! I bet you've come across a horse whose poll or back issues just kept coming back, despite regular bodywork sessions, tack alterations, and dental checks. A lot of the time this is because there is an underlying issue we are not addressing. And the underlying issue is very often just that – underlying. Very often it is found on the underside of the horse. A tight groin, a troublesome gelding scar, pectoral tears, diaphragm restrictions – all these are very common among horses.
With dysfunction in a living body, there are very few hard-set rules. Compensation comes in various shapes and sizes and each horse will cope differently, but here are some signs that might indicate a ventral line issue.
A clearly visible »ulcer line«.
A camped-under stance. A horse that's standing with his hind legs positioned far under his body does not have a balanced posture. This problem is usually multifaceted and requires a whole-house approach, but one of the common ingredients of the issue are restrictions in the groin and diaphragm
An »ulcer line«. A pronounced line going from the ventral side across the last few ribs is sometimes referred to as the ulcer line. This line can indicate excessive tension in the abdominal muscles, which can sometimes be an indication of ulcers. A tight belly and intestinal issues often go hand in hand. (Note: The evidence for the significance of this line is anecdotal. More evidence on this topic is still needed. The learning never stops!)
A loss of swing through the ribcage. In order for the horse to use his back effectively, his ribcage must be free to move from side to side. This allows for lateral flexion. If you observe the horse walk away from you and the ribcage seems to be either stuck completely or only moving to one side, this can be an indication of restrictions in the breathing muscles. This is often seen in horses with respiratory issues.
Sensitivity to touch. A horse that resents having his belly touched is always a red flag. There is a reason for this sensitivity, they are not »just ticklish«.
A narrow stance in front. Horses that seem to have a »base narrow« conformation often just have poor posture due to underdeveloped muscles of the thoracic sling. Weak, narrow pectoral muscles indicate that the horse is not using his body correctly.
This is in no way an exhaustive list, but it's a place to start. The next time you are out with your horse, observe his ventral line, the movement of his ribcage, and his stance. It could give you a clue about any issues he might be struggling with.
We talk about a camped-under stance when the metatarsal bones are not perpendicular to the ground.