Environmental Engineering Reference
In-Depth Information
flexible pastern and fetlock joints are of great help. They
browse readily on hedgerow and oddland grasses, and
they can even graze on aquatic plants while completely
submerged. During slack periods, grasses and rice straw
are enough to keep them fit. They mature fast and are
superior converters of feed (43 MJ/kg of gain compared
to cattle's 78 MJ/kg). They are docile (children are often
in charge), are easily trained (a week may be enough),
and can work for at least 10-15 years, although 25 years
is not uncommon.
The working hours of draft animals were dictated by
the pulse of seasonal cropping, and the annual totals
were 130-140 days for buffalo in China's double-
cropped fields but only 60-80 days for horses in single-
cropped agricultures of North China or Central Europe
(where the animals were used extensively for transport).
Workdays lasted from 4-5 h to 8-12 h. In plowing,
invariably the most difficult task, the daily performance
ranged from as little as 0.15 ha for a single buffalo in
wet fields to 0.5-0.8 ha for a good pair of horses during
a long day of stubble plowing or grassland breaking. In
the late-nineteenth-century United States gang plows
pulled by a dozen horses could finish 1 ha in just 2.5
hours. In intensive traditional farming, animals usually
worked no more than 1100-1400 h annually. Annual
useful work, with average ratings about 500 W for oxen
and buffalo and 700 W for horses, would be equivalent
to 2-3.5 GJ for every healthy animal, or 10-20 MJ for
every day of work.
The energetic value of working animals in comparison
with manual labor is clear. Compared to maximum sus-
tained human exertions at 50-100 W (mean 75 W),
draft animals commonly used in fieldwork can deliver
400-800 W (average @600 W), typically an eightfold
and usually not less than a sixfold difference. Moreover,
during numerous critical periods marking the course of
every cropping year, when speed is essential for timely
planting, harvesting, or storage, a well-fed animal can
work long hours for a few days and accomplish close to
30 MJ/day of useful work, more than 13 times what a
good human laborer could do. The question is, How
much of an energy burden were the animals for a tradi-
tional farmer?
According to NAS (1978), the maintenance require-
ments of a mature 500-kg horse are about 70 MJ/day
of digestible energy. Depending on the shares of highly
digestible concentrates (corn, oats) and less digestible
roughages (hays, straws), this may represent a very broad
range of required gross feed energies, but values between
80 MJ/day and 100 MJ/day (90 MJ/day average) were
most common. For actual working requirements we can
rely on Brody's (1945) impeccable metabolic measure-
ments: a 500-kg Percheron working at a rate of about
500 W metabolized about 10 MJ/h; a 700-kg horse
delivering 750 W metabolized 14 MJ/h. With 8 h of
work and 16 h of rest (at 3.75 MJ/h), this translates to
140-170 MJ/day. Half a century later Perez et al.
(1996) confirmed this result: the daily energy expendi-
ture of Chilean draft horses used for plowing was 2.24
times their maintenance requirements.
These values are confirmed by traditional feeding rec-
ommendations. Around 1900, U.S. farmers were advised
to feed working horses 4.5 kg/day of oats and 4.5 kg/
day of hay (Bailey 1908). During the 1910s an average
horse was fed daily 1 kg of oats, 2 kg of corn and 4.5 kg
of hay (USDA 1959). The Chinese norm issued in 1955
prescribed 7 kg/day of roughage (straw or grass) and
2.75 kg/day of unhusked grain (O. L. Dawson 1970).
These amounts translate, respectively, to about 150,
120, and 125 MJ/day. The last two values are long-
