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millennium essay

NATURE | VOL 405 | 11 MAY 2000 | www.nature.com 125

Vaclav Smil

Horses make superior draught animals.Unlike cattle, their front ends areheavier than their rears (by a ratio of

3:2), an advantage in inertial motion. Theycan stand without engaging muscles andhence without additional metabolic cost by locking their legs with suspensory liga-ments and a pair of tendons. And they growlarger and live longer than cattle, and havegreater endurance.

Medieval Europe adopted collar harness-

es and iron horseshoes just before the end ofthe first millennium. Ancient throat-and-girth harnesses choked the animal duringheavy exertion, and breastband harnessesprecluded the optimal transfer of power;fitted and padded collar gave a desirablylow traction angle while deploying power-ful breast and shoulder muscles withoutrestricting breathing. Iron horseshoes savedhooves from excessive wear and improvedtraction, and swingletrees, attached to tracesto equalize the strain resulting from unevenpulling, made it possible to harness an evenor odd number of horses.

By 1000, horses were thus mechanicallyready for a bigger role in medieval society and yet it took them several centuries to dis-place oxen as the principal draught animals.The Domesday count of 1086 shows that amere 5 per cent of all demesne draught ani-mals, and about a third of the total on Englishpeasant holdings, were horses. By 1300 theymade up nearly half of all draught animalsowned by peasants. But it was more than 200years before they became dominant. The sizeof the animals, their nutrition, and theploughs they pulled explain why.

The body weight, and hence power, of

draught horses only began to rise after sever-al centuries of breeding the heavy war ani-mals needed to carry armoured knights. Andmore powerful horses needed at least someconcentrates, such as cereal or legumegrains, in their diets not just theroughages (grasses, straws) fed to cattle.Farming had to be intensified to provide thisfeed for both people and animals. This was aslow process: in England, crop harvests werestagnant for centuries, and average yieldsonly took off in the late eighteenth century.

But even larger, well-fed horses had atough time with wooden ploughs. Theploughs heavy soles, wheels and mould-boards generated enormous friction, partic-ularly in wet soils, and without a smooth,curved fitting between the share and the flatmould-board, they were constantly clogged

with soil and weeds. Iron mould-boards onlycrossed from China to Europe in the seven-teenth century, and it was not until the rise ofthe modern steel industry in the mid-nine-teenth century that smooth, curved, steelploughshares replaced cast-iron shares.

Increased body size, improved feed quali-ty and cheap steel transformed draughthorses into unrivalled energizers of the earlymodern worlds agriculture. Horses werealso essential during the initial stages ofindustrialization, powering road and canaltransport, and turning whims in mining,

food processing and numerous manufac-tures before they were displaced by steamengines.

Heavier draught animals made it possibleto cultivate the existing fields more frequentlyand to convert forests and grasslands to newfields more easily, and freed labour for otheractivities. Most notably, the post-1850ploughing-up of Americas enormous grass-lands could not have proceeded so quicklywith oxen. The heaviest nineteenth-centurybreeds French percherons, English shires,German rheinlanders approached and

even topped 17 hands and weighed aroundone tonne. During brief exertions such horsescould develop about three horsepower, andthey could work steadily at rates well surpass-ing one horsepower (745 W). These animalsneeded a lot of feed, but their energy advan-tage was indisputable: a horse eating 4 kg ofoats a day consumed about the same amountof grain as six people but its power couldsupplant that of at least ten strong men.

By the 1890s, American horses, workingin teams of more than 30 animals, pulled notjust multishare ploughs but also the first

grain combines. Such large numbers of ani-mals needed abundant farmland: when thenumber of farm horses in the United Statespeaked at 21 million in 1919, at least 20 percent of the countrys farmland was needed tocultivate their feed. By that time internal-combustion engines and electric motors hadalmost totally displaced draught horses inthe cities of industrial countries.

Their eventual replacement in Westernfarming was inevitable: even the small inter-nal-combustion engines mounted on thefirst tractors could replace at least ten horses and claimed no land. By the end of 1960,

when three million horses were still left onAmerican farms, the US Department of Agri-culture stopped counting draught animals.The millennium of gradually expandinghorse power that was so instrumental in therise of the West ended in a rapid retreat. Vaclav Smil is in the Department of Geography,

University of Manitoba, Winnipeg R3T 2N2, Canada.

Horse powerThe millennium of the horse began with a whimper, but went out with a bang.

It took severalcenturies for horsesto displace oxen as the

main draught animals.

Pulling power: better harnesses and ploughs put horses efforts to more efficient use.

KITHOUGHTON/

CORBIS

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