Proteins contained in milk are a common cause of food allergies, particularly in infants. It is believed that casein proteins in the milk are the substances that cause such allergies. The types of casein differ according to what kind of milk they are present in -- an individual may, for example, be allergic to sheep-milk caseins, but not cow-milk caseins. Consult your doctor for advice concerning possible milk-related allergies, and the possibility of a diet excluding any caseins to which you are allergic.
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The caseins in cow milk may include different forms, with cow milk typically containing one of two types of beta casein. A study, published in the "Journal of Applied Genetics" in 2007, explaisn that, depending on an individual cow's genetic profile, the milk produced will contain either A1-beta caseins or A2-beta caseins. Digestion of A1-type casein can produce casomorphins, peptides with an opiate-like effect on your brain. A1 caseins are most common in milk from Holstein-Friesian, Ayrshire and Red breeds of cattle. A2 caseins are more commonly found in milk from Jersey and Guernsey cattle.
Goat's milk typically contains very low levels of Alpha-S1 casein, a type of protein considered difficult to digest. Low Alpha-S1 casein levels lead to a lower curd tension in goat's milk than in cow milk -- the relatively light and small curd in goat milk may be relatively easy to digest. In terms of beta caseins, goat's milk typically contains the A2 type. Goat's milk is sometimes recommended for those attempting to avoid A1-beta casein in the diet.
A study published in the August 1999 issue of the journal "Clinical and Experimental Allergy" indicates that certain individuals may be sensitive or allergic to sheep caseins. The experiment involved skin-prick tests using sheep, goat and cow milk, casein and cheese. Only one individual was involved in the experiment, and it was proven that his allergy was specifically to sheep and goat caseins -- he was not allergic to the caseins in cow's milk.
Certain caseins can be isolated as the likely cause of an individual's milk allergies. A1-beta caseins have been implicated in the development of certain health problems. A 1999 report published in the journal "Diabetologia" indicates that A1-beta caseins may increase the risk of developing Type 1 diabetes. Commercial milk producers are now aiming to select farm animals that produce milk containing A2-beta caseins. Consult your doctor for medical advice specific to your health background and dietary allergies.