Abstract
The dairy sheep industry is an important but lacking part of the small ruminant industry. For a sheep breeding program, in addition to wool and meat use, sheep milk can also be processed into high-end dairy products such as cheese and milk powder and bring high economic interests for businesses home and abroad. With increasing interest in sheep milk, the content of which is becoming increasingly clearer, people have found that the nutritional value of sheep milk is higher than that of goat milk and cow milk, with abundant fat yield, protein percentage, and mineral contents, which provide a good opportunity for the development of the sheep milk industry. This review will introduce some dairy sheep breeds with the highest milk production worldwide and compare sheep milk nutrition contents with other ruminants’ milk. Moreover, genes influencing lactation or mammary gland growth like CSN2, SLC2A2, SCD, and SOCS2, which have been revealed in recent studies to significantly affect milk production and milk composition traits will be discussed. For the SLC2A2 gene, working as an important solute carrier to transport small molecular nutrition from blood to milk and SOCS2 gene mutation as an indicator of mastitis, in addition, other genes have been detected that correlate with milk traits, which will be introduced in the review. Some personal opinions into future sheep milk development will be given in the final part of the text. Although the research of sheep milk genetic factors has achieved some progress in recent years, there is still a long way to go.
Highlights
Sheep were domesticated in Southwest Asia approximately 11,000 years ago and are raised around the world for meat, wool, and milk use
A large quantity of dairy sheep are distributed in Mediterranean and Black Sea regions, so the sheep milk industry is mainly concentrated in parts of Europe, West Asia, and African countries such as France, Greece, Italy, Spain, Israel, Turkey, and so on; some dairy sheep breeds like the East Friesian sheep, Sarda sheep, Lacaune sheep, Latxa sheep, and Assaf sheep are all high producing sheep breeds known to the world [3]
Sutera, A.M. carried out GWAS for milk production traits in 469 Valle del Belice sheep using repeated measures, and the research found SNP rs425417915, which is located in an intronic region of TTC7B gene, to be associated with both fat percent and protein percent, playing a critical role in lipid metabolism in cattle and was reported to be associated with fat yield (FY) composition in sheep [72]
Summary
Sheep were domesticated in Southwest Asia approximately 11,000 years ago and are raised around the world for meat, wool, and milk use. The province of Friesian is the birthplace of both Holstein cows and East Friesian sheep The two breeds both have the highest milk production among ruminants in the world. East Friesian sheep is a high-yielding dairy sheep breed generated through long-term good feeding management and genetic improvement and has been imported to many countries. Due to its good milk and meat production performance, the male parent was always imported as to improve local breeds in various countries. Until today, these countries have developed corresponding dairy sheep breeds that are suitable for local conditions [10]
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