Food Biochemistry and Food Processing (2 edition)

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494 Part 4: Milk

been used successfully as a substitute for human milk in West-

ern Europe (Vincenzetti et al. 2008) and is the milk of choice in

Italy for children with severe immunoglobulin E (IgE)-mediated

cows’ milk allergy. (Businco et al. 2000).

Production of Equid Milk

The production of equine milk and the factors that affect it have

been the subject of several reviews, including Doreau and Boulot

(1989), Doreau et al. (1990), Doreau (1994), Doreau and Martin-

Rosset (2002) and Park et al. (2006) and, therefore, is considered

only briefly here.

World milk production was approximately 695 million tonnes

in 2009, of which 84% was bovine, 13% buffalo and 3% sheep,

goat and other species (IDF 2009). Statistics for milk production

from species other than cows and buffalo are not very reliable

and are available only from countries where these milks are

processed industrially although it is accepted that, while bovine

milk production figures have changed little in recent years, the

production of milk from buffalo, camels, horses and donkeys is

increasing. In Europe, it is estimated that about 1–1.3 million

litres of equine milk are currently produced per annum but in

countries such as Mongolia the figure is considerably higher,

probably approximately 9 million litres.

A decade ago, equine milk was produced only in isolated

small holdings in parts of Eastern Europe and Mongolia, but

now there are large-scale operations in France, Belgium, Ger-

many, Austria and the Netherlands. Asinine milk is produced in

large donkey farms in Italy, France, Spain, Belgium, Xinjiang

and Shanxi provinces of China, Ethiopia and Pakistan (Salimei

2011).

For equine milk production, milking begins when the foal

reaches approximately 8 weeks and is eating some hay and grass.

The mare is separated from the foal by day and milked approx-

imately five times at intervals of about 2.5 hours and produces

1–1.5 L of milk at each milking. At night, the foal feeds freely

(van Laar, Orchid’s Paardenmelkerij, the Netherlands, personal

communication). Thus, milk production is very labour intensive

and expensive, with the result that equine milk is priced as a del-

icacy, typically,€11/L. Milking schedules are similar for asinine

milk, but the yield is lower than that of the horse, approximately

350–850 mL of milk per milking, depending on several fac-

tors including: foal and mare management, milking procedure,

stage of lactation, body size and condition and feeding regime

(Salimei 2011). Mastitis is rarely a problem with equids and

occurs only if teat injury occurs during milking. Furthermore,

equid species appear to be relatively resistant to brucellosis and

tuberculosis, which is advantageous from a dairy farming point

of view (Stoyanova et al. 1988).

COMPOSITION OF EQUID MILK

With the exception of the major domesticated dairy species and

humans, information on milk composition is poor and of> 4500

mammalian species in existence, milk compositional data are

available for approximately 200 species, of which, data for only

approximately 55 species appears to be reliable. The milk of all

mammals contains the same principal components: water, salts,

vitamins, fats, carbohydrate and proteins, but these constituents

differ significantly both quantitatively and qualitatively between

species (Table 26.1), although species from the same taxonomic

order, for example equids, produce milk of similar composition

(Table 26.1). Equid milk is similar in composition to human

milk but considerably different from that of other dairy mam-

mals, for example cow, buffalo, sheep, goat, camel, llama and

yak (Table 26.1). Why equid milk is so similar in macro compo-

sition to that of human milk is unclear, especially as equids and

humans are phylogenetically distantly related. Inter-species dif-

ferences in milk composition reflect very divergent patterns of

nutrient transfer to the young and presumably reflect adaptations

in maternal rearing of offspring to physiological constraints and

environmental conditions (Oftedal and Iverson 1995). In all sit-

uations, lactation must be effective in providing nourishment to

the offspring without over-taxing maternal resources.

The protein content of milk varies considerably between

species and reflects the growth rate of the young. Bernhart

(1961) found a linear correlation between the percent of calories

derived from protein and the logarithm of the days to double

birth weight for 12 mammalian species. For humans, one of the

slowest growing and slowest maturing species, it takes 120–180

days to double birth weigh and only 7% of calories come from

protein. In contrast, carnivores can double their birth weigh in

as little as 7 days and acquire>30% of their energy from pro-

tein. Equid species take between 30 and 60 days to double their

birth weight and, like humans, have an exceptionally low level

of protein in their milk (Table 26.1). The high metabolic needs

of the foal are met through frequent feeding. Equid milks have

a significantly lower energy value than human milk, owing to

their low fat content (Table 26.1).

The fat content of milk across species shows large variation

and ranges from approximately 0.6% for some breeds of donkey

and less than 1% for rhinoceros to approximately 50% in the milk

of some seals. High-fat milks are important for some species,

for example desert mammals, when maternal water economy is

important and energy needs to be transferred to the young in an

efficient manner. Equid milk has one of the highest contents of

carbohydrate, which is similar to that of human milk. In equid

species, lactation lasts naturally for approximately 7 months.

Factors that Affect the Composition

of Equid Milk

Stage of Lactation

Within species, the stage of lactation is the most important

determinant of milk composition and the difference between

colostrum and mid-lactation milk shows the most significant

difference but absolute values and the direction of change

vary among species (Casey 1989). Shorty after parturition, the

mammary gland produces colostrum that is richer in dry mat-

ter, proteins, fat, vitamins and minerals (except calcium and

phosphorus) but poorer in lactose than mature milk. One of the

major biological benefits of colostrum is the presence of Igs,

IgA, IgM and IgG, and high levels of some enzymes, including