Method for determining size of the hitch
A basic approach to determining the kind and number of animals required is to estimate the maximum power the farmer will need and then calculate the size of the animal or team of animals that could supply it. The combination of animals that will satisfy the farmer's power needs is called a hitch. The size of the hitch can be determined by using the tables below, or by making the calculations found in Appendix A.
Table 2 gives the draft requirements of various field operations. Remember that the draft requirement is the amount of power needed to pull an implement through the soil.
Tables 3 and 4 give the amount of power donkeys and bulls, respectively, can deliver in relation to their body weight and number of individuals in the hitch.
To determine the kind of hitch needed, first find the draft requirement of the most difficult operation to be performed (Tables 1 and 2). Use Tables 3 and 4 to find which size animal or combination of animals will deliver this amount of power. Then determine the weights of the available animals to match animal power to draft requirements.
Difficulty of work-The most difficult field operation will be plowing fairly light soils during the rainy season with a single moldboard plow. The farmer's fields are old (have been cultivated the previous season) and plowing depth will not exceed 15 centimeters (cm).
Draft requirements-According to Table 1 about 70 kg of pulling power are needed to do this kind of work.
Hitch options-Tables 3 and 4 can be used to determine two hitches that would satisfy the draft requirement:
1) two 300-kg bulls (69.5 kg of power or draft)
2) four 110-kg donkeys (69 kg of power or draft).
Table 1-Requirements of Some Farm Implements for Operations on Medium Loam Soils*
*See Chapter 7 for a description of these operations and implements.
Table 2-Draft Requirements of Field Operations
Choice of hitch-The decision is made based on these criteria: availability of animals, cost of animals, daily work potential of animals, cost of harness, and availability and cost of feed.
If they are available and the farmer can afford them, bulls are generally the best choice because they will work longer hours per day and they require less harness equipment. Bulls weighing less than 300 kg each could be used if they were harnessed in breastbands or collars rather than in a yoke. Animals can deliver more of their potential power when working in these types of harnesses.
Table 3-Power of Donkeys (in breastband or collar)
If animals to be used are of the same size, match draft requirement to figure in TOTAL columns. For example, an animal owner could meet a requirement of 56 kg of power by using two 150-kg donkeys, three 110-kg donkeys, or four small animals of 90 kg apiece.
If animals are of different sizes, use single animal column for any size hitch, and add individual power together to get hitch total.