Appendix A: Animal power

The formulas below can be used to approximate the size of the hitch (animal or animals) which will supply the desired amount of power. "W" is the weight of a single animal, "d" is the draft requirement (this is taken from the chart), and "c" is the animal's power coefficient. For a bull, "c" is 8 or 1/8 of W); for a donkey, it is five (or 1/5 of W). If animals will be working new or hilly land, or will be harnessed in yokes ratner than collars or breastbands, coefficients should be increased to 9 or 10 for bulls, 6 or 7 for donkeys.

The first two formulas (below, A and B) are used to calculate the weight of animals that will be used alone; the other formulas allow for the losses of efficiency that result when multiple hitches are used.

Assuming a farmer needed draft unit that supplied a tote" of 57 kg of force, the following calculations would be made.

W = (57 x 8)/1.85 or W = 246

or, each of two bulls would have to weigh 246 kg. (Note that, used alone, this animal will supply 1/8 x 246, or 30.8 kg draft. In a team of two, it is 7.5% less efficient, supplying only 28.5 kg draft-or half of the 57 kg needed.

A One bull	W = 1/8 d
B One donkey	W = 1/5 d
C Pair of animals	W = dc/1.85
D Team of three animals	W = dc/2.55
E Team of four (tandem pairs)	W = dc/3.12
F Team of five	W = dc/3.5
G Team of six	W = dc/3.78

W = (57 x 5)/1.85 or W = 154

If the farmer could not buy or obtain a pair of bulls, the donkeys might be a practical alternative. However, donkeys work only 3-4 hours per day, so the farmer might consider buying two pair and working them in separate morning/afternoon shifts. If the doneys in the area were of a small breed, it might take three or four animals to deliver the necessary power:

W = (57 x 5)/2.55 or W = 112

or each of three donkeys would have to weight approximately 112 kg. Or

W = (57 x 5)3.12 or W = 91

or each of four donkeys would have to weight about 90 kg if the draft requirement of 57 kg were to be met.