Draught-Animal Harness Efficiency: The Collar Pressure Bound on Sustainable Pull

Working horses and oxen lose working capacity, and can be injured, when a harness concentrates the draught force on too small an area of the body. This paper models force transmission through a full collar and through a breastband, and derives the maximum draught force each can sustain over a working day before soft-tissue pressure, and for the breastband airway pressure, reach stated limits. For a horse of 600 kg, the collar bound is 704 N, or 12.0% of body weight, while a well-fitted breastband is bound at 228 N, or 3.9% of body weight, a ratio of 3.09. If the breastband rides up so that a larger share of the force bears on the trachea, its bound falls to 111 N, or 1.9% of body weight. For an ox of 700 kg the corresponding bounds are 880 N (12.8% of body weight) for the collar and 274 N (4.0% of body weight) for the well-fitted breastband. The model gives a simple sizing rule: a collar needs at least 1.70 cm2 of effective contact area per newton of sustained draught, or 170 cm2 per 100 N. Checked against representative tasks, even a light cart on a flat, firm road, requiring 235 N, already reaches the well-fitted breastband bound for a horse, and ploughing and graded or soft-ground cart work exceed the breastband bound by large factors. The negative results are stated at full size: in heavy, wet soil the required plough pull exceeds even the collar bound for a pair by a factor of 3.05 per horse, so no change of harness makes that task sustainable - the team, the implement, the soil condition, or the task itself must change. SIMULATED, NOT MEASURED: this is a modelling study; nothing was built, fitted to an animal, or tested on an animal. AI disclosure: This paper was drafted with the assistance of Dave, an AI system, at the direction of the author.