Dairy products represent an important food source for people worldwide, but milk products from horses and donkeys occupy a very small niche indeed.
These “minor milks” and their related products have long been relegated to a “dark” area of research because of poor economic significance, a just-published review points out.
However, increasing interest in ethnic foods and alternative milk products are now shining a light on them, Michele Faccia and colleagues note in their paper recently published in the open-access journal Animals.
Faccia, together with Angela Gabriella D’Alessandro, Andrea Summer and Yonas Hailu, set out to in their review to delve into the milk products available from minor dairy species.
Milk processing is one of the most ancient food technologies, dating back around 6000 BC, the review team points out. For dairy processing through the millennia, the ability of milk to form a gel by acidification or renneting has been pivotal.
Today, cattle produce 82% of the world’s milk. The remaining share is mostly obtained from buffaloes, goats, and sheep.
Less than 1% is derived from other animals, such as camels, horses, donkeys, and yaks, all defined as “minor dairy species”.
Their review, which cites 187 scientific papers, notes that the minor dairy species have low economic significance and, consequently, research into their milk-related products has only recently started.
Scientific information about mare and camel milk goes back only 30 years or so, while for other species, such as donkeys and yaks, investigation has increased in the last 20 years.
“A significant number of publications on minor dairy products are now available, and it is clearly emerging that they represent not only a priceless cultural heritage but also a source of innovative and, in some cases, healthy foods.”
The review team set out to explore what is known about milk from horses, donkeys, camels, and yaks.
The world horse population is estimated at more than 60 million, and the donkey population is believed to be about 56 million.
The chemical and nutritional characteristics of horse and donkey milk are similar, and both differ considerably from that of the principal dairying species, the authors note.
“In comparison with cow milk, they contain less total solids, fat, and protein and more lactose, showing a composition close to that of human milk.”
However, the poor dry matter content makes gelification difficult, but other concerns derive from the composition of the protein fraction. In particular, casein and whey proteins comprise less than one-third of the levels found in cow’s milk.
Few studies are available in the literature regarding somatic cell content and total bacterial counts in equine milk.
“In general, the studies agree that the values are rather low, and for somatic cell counts, they are lower than cow milk.”
As in cows, the inflammatory state of the udder is the main reason for the increase in somatic cell counts. Mares have a generally good health status for their mammary gland and good microbial quality of milk due to the low volume of udder, high resistance to pathogens, and high concentrations of antimicrobial compounds.
Thermal treatment before consumption is always recommended, in particular in those regions of the world where horses, donkeys, and mules are crucial components of micro‐economies and the prevalence of Brucella species and Rhodococcus equi is higher.
The authors note that the consumption of horse milk is widespread in the world, with 30 million people drinking it more or less regularly. Dairy herds are mainly located in the former USSR and in Mongolia.
Kazakh breeds are probably the most significant, having been selected over many years for milk production, while, in Western Europe, the main dairy breed is the Haflinger.
Conversely, no selection has been carried out for donkey milk production, and there are no specialized dairy breeds.
“Milk from both the species has historically held a special place,” they say. “In particular, horse milk is a traditional food for the nomadic pastoral populations of Asia, while donkey milk was widely known in ancient popular tradition as a substitute for breast milk for infants.”
The functional peculiarities of horse milk, linked to protein content, casein concentration, distribution of diglycerides and triglycerides, and proportion of polyunsaturated fatty acids, have led to it being considered more suitable for human nourishment than cow milk.
“It is also considered a possible substitute of cow milk for children affected by allergy to cow milk proteins due to its similarity to human milk, palatability, and low allergenic properties.”
In addition, several other health benefits have been attributed to Equidae milk. This has led to equine milk being considered a functional/nutraceutical food suitable for sensitive consumers.
As a result, it has stimulated growing scientific and entrepreneurial interest in milk for human nutrition, as well as in manufacturing dairy products.
The most famous dairy product obtained from horse milk is koumiss, also called kumis, airag, or chigee. It is a traditional lactic‐alcoholic beverage that has been produced since around 2000 BC and is best known and widely consumed in the central Asian regions, in some regions of Russia and China, and in Mongolia.
It is obtained from fresh raw milk inoculated with a bulk starter (mainly lactic acid bacteria and yeast) at 20–30% dose and kept in a suitable animal hide bag for fermentation at, usually, 20–30 degrees Celsius.
The major limitation for its production is the scarce availability and high cost of mare milk, so methods have been defined to substitute it with cow milk after modification by rendering its composition similar to that of mare’s milk (dilution, removal of fat, lactose addition, and filtration).
The manufacturing process of koumiss is now more standardized, with the use of wooden vats, plastic barrels, or stainless steel tanks in place of the leather containers, selected starters, and control of the inoculation temperature.
Koumiss has a milky‐bluish‐white color with a pinkish tinge, a sour and slightly tart taste, a slightly sweet aftertaste, and a characteristic almond flavor.
Donkey milk has also traditionally been used to produce koumiss‐like products.
“Making cheese from equine milk is considered not feasible due to the concerns in rennet coagulation,” they continued.
Making cheese from donkey milk
“Nevertheless, several recent studies have shown it is possible to produce cheese from donkey milk by following dedicated technological approaches such as the use of particular types of rennet, strong coagulating conditions, fortification with milk from other species, and addition of transglutaminase in order to better crosslink the milk proteins.”
In 2015, an Italian scientist obtained a fresh cheese prototype by using camel chymosin.
Donkey milk has also been used to make cheese, but it was fortified with goat milk, or in another case cow’s milk.
The review team said different types of rennet can be used for donkey-milk cheese-making, but the curd obtained is always weak and is only suitable for making fresh cheese.
“The main problem remains the high cost of the product, which could be overcome only by increasing the milk productivity of the animals.”
In their conclusion, the authors noted the range of traditional milk products that have been produced from the minor dairy species. Some could be promoted in niche markets, together with new types of products increasingly being developed by researchers.
“However, much work is still needed to create specific production chains; the main challenges are to standardize the technological protocols and to complete the chemical‐nutritional and microbiological information.
“These challenges should be faced with an interdisciplinary approach, in which animal scientists and food technologists interact for increasing the production volume in connection with some particular qualitative aspects.”
Faccia, M.; D’Alessandro, A.G.; Summer, A.; Hailu, Y. Milk Products from Minor Dairy Species: A Review. Animals 2020, 10, 1260.