Animal traction |

**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.**

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