Holsteins are the most widespread dairy breed in the world. They have been genetically improved to produce a higher yield and become more profitable for the dairy industry. The first Holsteins were born in Europe around 2000 years ago (1). They originate from the Netherlands, in the provinces of North Holland and Friesland. The crossing of black Batavian cattle and white Friesian cattle produced a black and white cow that could exploit the rich pastures of the Rhine region. Such crossbreeding allowed the digestive system of Batavian cattle and the body and udder size of Friesian cattle to produce an efficient and highly productive dairy cow (1). Holsteins are a versatile breed of cattle. They are adaptable to all types of different uses. This breed can thrive in both the barn and pasture or a mixture of the two throughout the year. With such versatility, Holsteins resist stress and produce strong, robust calves that have rapid growth and an early maturity rate. Although Holsteins are resistant to stress, they have intolerance to heat and disease. The consequence of such intolerance is a reduction in milk productivity (1). Even with naturally high milk production, years of selective breeding have further increased this yield. Since the 1960s, the U.S. dairy industry has significantly improved its selective breeding efforts, helping to double milk production (2). With this major development, it is likely that genetic improvements could increase by 1 to 2% per year (1). Currently, 30% of the Holstein genome has been modified by selective breeding procedures. These changes can be illustrated by an increase in milk production. Between 1957 and 2007, milk production increased by...... middle of paper .......holsteinusa.com/holstein_breed/breedhistory.html. Holstein Association USA.5. www.ars.usda.gov/is/pr/2007/070109.htm. United States Department of Agriculture: Agricultural Research Service.6. http://www.biotech.iastate.edu/biotech_info_series/Bovine_Somatotropin.html. Bovine somatotropin (bST).7. Santos J, Juchem S, Cerri R, Galvao K, Chebel R, Thatcher W, Dei C, Bilby C. Effect of bST and reproductive management on reproductive performance of Holstein dairy cows. Journal of Dairy Sciences. 2004;87:868-881.8. www.ars.usda.gov/is/pr/2002/020920.htm. United States Department of Agriculture: Agricultural Research Service.9. Kerr D, Wellnitz O. Breast expression of new genes to combat mastitis. Journal of Animal Sciences. 2003;81:38-47.10. www.ciwf.org.uk/includes/documents/cm_docs/2009/f/factsheet_dairy_cows_dec08.pdf. Factsheet on Compassion in Global Agriculture.