Food Biochemistry and Food Processing (2 edition)

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492 Part 4: Milk

casein and more whey proteins. The low fat and unique fatty acid

profile of both equine and asinine milk result in low atherogenic and

thrombogenic indices. The high lactose content of equid milk gives

good palatability and improves the intestinal absorption of calcium

that is important for bone mineralisation in children. The renal load

of equid milk, based on levels of protein and inorganic substances,

is equal to that of human milk, a further indication of its suitability

as an infant food. The concentration of lysozyme, lactoferrin and

n-3 fatty acids is exceptionally high in equid milk, suggesting a

potential anti-inflammatory effect. Equine and asinine milk can be

used for their prebiotic and probiotic activity and as alternatives for

infants and children with cow milk protein allergy and other food

intolerances.

While the gross composition of equine and asinine milk has been

reasonably well established and the caseins have been fractionated

and well characterised, the presence ofκ-casein remains a con-

tentious issue and there is little or no information on the physico-

chemical properties of equid milk. The only significant product from

equine milk is the fermented product, koumiss.

The composition of equid milk suggests a product with inter-

esting nutritional characteristics with potential use in dietetics and

therapeutics, especially in diets for the elderly, convalescent and

newborns, but the lack of scientific research must be addressed to

develop the potential of equine and asinine milk in the health and

nutritional markets.

INTRODUCTION

Approximately one-third of all mammalian genera are herbi-

vores, more than half of which belong to two orders, (1) the

Perissodactyla (odd-toed ungulates (hoofed animals)) and (2)

the Artiodactyla (even-toed ungulates) (Savage and Long 1986).

The horse and donkey belong to the order Perissodactyla that

has three families: (1) Equidae (nine species of horses, don-

key and zebras), (2) Tapiridae (four species of tapirs) and (3)

Rhinocerotidae (five species of rhinoceros). Uniquely among

species, all Equidae can interbreed, but the hybrid offspring

are almost always infertile because horses have 64 chromo-

somes and donkeys have 62 chromosomes (Trujillo et al. 1962).

Zebras have between 32 and 46 chromosomes, depending on

breed (Burchelli’s zebra,Equus burchelli, has 44 chromosomes,

Carbone et al. (2006) and viable hybrids with donkeys have

been produced where gene combinations have allowed for

embryonic development to birth. Differences in chromosome

numbers between horses and zebras are most likely due to

horses having two longer chromosomes that contain a single

gene content compared to four zebra chromosomes (Benirschke

et al. 1964).

This chapter presents a brief historical overview of some as-

pects of the domestication of equid species, a review of the chem-

istry and biochemistry of the principal constituents of equine

milk and, to a lesser extent, of asinine milk, with comparative

data for bovine and human milk. The technological properties

of equid milk, with reference to processing of the milk are ex-

amined and, finally, a synopsis of the nutritional and biological

significance of equid milks in the human diet is presented.

Equid Evolution

Perissodactyla species evolved during the early Eocene (∼ 55

million years ago) and were the dominant ungulate order un-

til approximately 15 million years ago when numbers declined,

probably due to climatic factors rather than competition with

emerging Artiodactyla species (including the Ruminantia fam-

ily) (MacDonald 2001). Nevertheless, wild equids ranged in vast

herds across the grasslands of the Northern Hemisphere and

in South America until the end of the ice age, approximately

10,000 years ago. Wild horses were the chief prey of increasing

human populations and numbers decreased until they became

extinct in North America approximately 7000 years ago and in

Europe, herds of horses were pushed eastwards into Central Asia

where the last few Przewalski horses (Equus ferus przewalski)

survived until the twentieth century (Clutton-Brock 1992). It

is generally assumed that equids were domesticated approxi-

mately 5000 years ago but archaeologists believe man did not

ride horses until approximately 1000bc, although horses re-

placed the ox as draft animals approximately 2000bc(Clutton-

Brock 1992). One of the early records of the domestic horse

in Western Europe comes from horse remains found at the late

Neolithic site at Newgrange, County Meath, Ireland (Clutton-

Brock 1992). Outram (2009) demonstrated domestication of the

horse in the Eneolithic Botai culture of Kazakhstan approxi-

mately 3500 years ago and analysis of organic residues based on

characterisation of stable isotopes of carbon,δ^13 C (which allows

differentiation of non-ruminant and ruminant carcass and dairy

fats) and deuteriumδD, values of fatty acid analysis revealed

processing of mares’ milk and meat in ceramics at that time.

The donkey (Equus asinus) is believed to have evolved from the

Nubian and Somalian sub-species of African wild asses approx-

imately 4000–5000 years ago and has since been an integral part

of human life as a pack and riding animal. Today, perissodactyls

are a poor second to artiodactyls in terms of numbers of species,

geographical distribution, variety of form and ecological diver-

sity (MacDonald 2001). For further details on equid evolution

and genetic lineages of domestic horse species, see Vilaetal.`

(2001) and references therein.

Equid Domestication

Only five major species of large, plant-eating mammals have

been widely domesticated: sheep, goat, cattle, pig and horse.

Nine additional minor species have been domesticated but are

restricted to certain geographical areas: Arabian and Bactrian

camels, llama, alpaca, donkey, reindeer, water buffalo, yak,

Bali cattle of Southeast Asia and the gaur (mithan) of India

and Burma (Bruns 1999). Despite taxonomic congruity and be-

havioural similarities between equid species, only two equids

have been domesticated: the horse (Equus ferus) and the donkey

(Equus asinus africanus) (Clutton-Brock 1992).

Because milk and products derived from it provide up to 30%

of dietary protein in developed countries, to meet this demand,

man has genetically improved some species for milk production

(Mercier 1986). Domesticated animals have been modified from

their wild ancestors through being kept and selectively bred for