Modification Of Milk Composition

Transfer of genes to alter milk composition has thus far received little research emphasis, but offers the dairy industry considerable potential for the future. A list of potential changes in milk components worthy of consideration is shown in Table 1.

About 80% of milk protein from cows is composed of caseins (S1, S2, and k), and whey proteins (b-lactoglob-ulin, a-lactalbumin, serum albumin, and g-globulin) make up the remaining 20%.

The caseins form the curds in cheese, whereas the whey proteins represent a less valuable by-product. Elimination of b-lactoglobulin from milk would benefit cheese production because it inhibits rennin's action on k-casein,[4] and would benefit certain fluid milk consumers because b-lactoglobulin is responsible for some milk allergies. Removal of b-lactoglobulin from cattle is now technically feasible during transfection of fetal fibroblasts that are then used for nuclear transfer.[7]

While removal of a-lactalbumin (a-lac) from cows' milk may be beneficial for some consumers, researchers at the University of Illinois have shown that increased concentrations of lactose, which result from a-lac expression, may be beneficial for piglet growth.[8] They produced transgenic pigs that express bovine a-lactalbu-min in their milk, which results in a higher milk lactose content in early lactation and a 20 to 50% greater milk yield on days 3 9 of lactation, compared to that of control sows. Weight gain of piglets suckling a-lac sows was greater at days 7 and 21 after parturition than that of control piglets. Thus, overexpression of a-lac milk protein provides a means for improving growth performance of piglets through enhanced lactation of sows.

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