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26 Equid Milk: Chemistry, Biochemistry and Processing 493use by humans who control the animals’ breeding and feeding.
Domestication of dairy species has meant that different breeds
of farm animals, for example dairy cows and goats, can be devel-
oped and maintained to optimise certain hereditary factors, for
example, length of lactation, period of gestation and milk yield,
as well as protein and fat levels in the milk produced. Genetic
selection of breeds of horse and donkey for milk production has
not occurred, as yet, and consequently there is high variability
for milk yield and length of lactation, as well as high individual
variability.
In some regions of the world, for example Mongolia and
Southern Russia, Hungary, France and Belgium, the horse and,
less frequently, the donkey, is an important source of meat
and milk. Steppe Mongols, forest-steppe Kazakhs, the Hadza
hunter–gatherers of Tanzania and the urban French all regard
horses as a valuable food source and believe that horse flesh and
milk have special nutritional and medicinal attributes (Levine
1998). The use of donkeys as a dairy species can be traced
back to Roman times when the nutritional value of its milk and
beneficial properties in skin care were first recognised (Salimei
2011).
The importance of the horse in leisure activities, especially
racing, has led to the scientific breeding and nutrition of horses,
including foals, and has created the need to characterise the
composition and properties of equine milk, which are now rela-
tively well known. The fact that the horse is spread throughout
the world, has been domesticated, is relatively easily handled,
and produces large amounts of milk, which can be obtained rel-
atively easily, makes equine milk a relatively easy subject for
research. Although the donkey is now less widely distributed
than the horse, its milk can be obtained readily. The zebra has
not been domesticated and although it is widespread in the wild
in Africa and in captivity elsewhere, apparently it is very dif-
ficult to obtain zebra milk, even from captive animals. Studies
of the social behaviour of equids have shown that there are no
intrinsic reasons why the zebra has never been domesticated but
it is believed that the peoples of Africa may have had cultural
rather than biological reasons not to use zebras as pack animals
(Clutton-Brock 1992).Ruminants and Non-RuminantsThe horse and donkey are non-ruminant herbivores and digest
portions of their feed first enzymatically in a foregut and then
ferment it in a very large sacculated hind-gut. Limited digestion
occurs in the equid stomach which liquefies incoming feed and
secretes gastric acid and pepsin to initiate breakdown of feed
components. The equid digestive system is designed to process
small amounts of food frequently (Sneddon and Argenzio 1998).
Equids rarely fast for more than 2–4 hours at a time and natu-
rally forage for 16–18 hours/day. Horses in the wild roam widely,
grazing both day and at night on immature, easily digested food
and exhibit few digestive problems in comparison to domesti-
cated horses (Sellnow 2006). Unlike ruminants, and in keeping
with their status as prey animals, horses do not require periods
of rest to stop and ruminate. Ruminants have very efficient di-
gestive systems with microbial breakdown of fibrous food at thestart of the gastrointestinal tract and nutrient absorption along
the entire intestine. Ruminants can digest fiber and carbohydrate
more completely than any other species.
Donkeys, like horses, generally survive on a diet high in fiber
and low in soluble carbohydrate and protein but while donkeys
are not as efficient as ruminants at digesting cell wall compo-
nents, they are far more efficient than horses (Izraely et al. 1989).
Donkeys are capable of consuming large amounts of forage and
gain more digestible energy from it than even goats fed a simi-
lar diet (Smith and Sherman 2009). The donkey achieves this by
substantially increasing its forage intake rate to compensate for a
low-quality diet. A donkey uses its narrower muzzle and prehen-
sile lips for greater selectivity of its food, thereby, maximising
feed quality rather than quantity (Aganga et al. 2000). Don-
keys have a much lower water requirement per unit weight than
any other mammal, except the camel, and can rehydrate quickly
with large volumes of water without complications. Donkeys
can work while suffering from severe dehydration by reducing
water and energy turnover rates, while maintaining feed intake
and its plasma volume can be maintained by drawing on the
substantial fluid reservoir in the hind-gut (Sneddon et al. 2006).
The zebra, on the other hand, needs a constant source of water
for survival (Aganga et al. 2000).Why Equid Milk in Human Nutrition?The benefits of equine milk for human health is an ancient idea
and there is much literature from the former Soviet Union on
this subject, although it is now accepted that the results of ex-
perimental work are dubious (Doreau and Martin-Rosset 2002).
Because equine milk resembles human milk in many respects
and is claimed to have special therapeutic properties, it is be-
coming increasingly important in Western Europe, especially in
France, Italy, Hungary and the Netherlands. Equine milk (and
koumiss, fermented equine milk) is often used for the treatment
of a myriad of ailments including anaemia, nephritis, diarrhoea,
gastritis disorders, cardiovascular disease and in post-operative
care, as well as for stimulation of the immune system (Lozovich
1995). In Mongolia, where koumiss is the national drink, people
have a saying that ‘kumys cures 40 diseases’ (Levine 1998). In
Italy, equine milk has been recommended as a possible substi-
tute for bovine milk for allergic children (Curadi et al. 2001).
Equine milk is considered to be highly digestible, rich in es-
sential nutrients and possesses an optimum whey protein:casein
ratio, making it very suitable as a substitute for bovine milk in
paediatric dietetics. Estimates suggest that more than 30 million
people drink equine milk regularly, with this figure increasing
significantly annually (Doreau and Martin-Rosset 2002).
The use of asinine milk by humans for alimentary and
cosmetic purposes has been popular since Egyptian antiquity.
Cleopatra is reputed to have bathed daily in asinine milk and
kept a herd of 700 to fill her bath. Hippocrates (460–370bc)was
a strong advocate of the use of asinine milk as a medicine and
used it to cure many ailments including, liver disease, oedema,
nosebleed, poisoning and wounds. Today, asinine milk is con-
sumed mainly in countries where donkeys were traditionally
bred, Asia, Africa and Eastern Europe but more recently it has