## Growth and development with special reference to domestic animals XXXIII: Efficiency of work horses of different ages and body weights

##### Abstract

A simple method is described for measuring the energy cost of work in horses. Data are presented on the energy cost of pulling graded loads at different speeds on a horizontal plane (treadmill). A large Percheron gelding, a Percheron colt and two Shetland ponies were employed in this work. It is shown that the gross or overall energetic efficiency of work under these conditions increases with increasing rate of work approaching an efficiency of 25% as a limit. If the overhead cost of standing at rest and of walking is deducted from the total energy expense then the resulting absolute efficiency is practically constant, and is of the order of 34%. It is shown that while the overall efficiency of work in large and small horses is the same if they are doing work at rates proportional to their body weights, yet the greater maintenance cost of large animals when at rest results in a relatively greater feed cost in larger animals, and, therefore, lower net efficiency. The detailed numerical data as well as graphs and equations relating the variables are presented for energy metabolism and cardiorespiratory activities.