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Milk Composition & Synthesis
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Milk Composition
Breed & Strain Variability


Breed or Strain Variability

The composition of milk also varies within a species. The dairy cow is a good example of this (see the images below). Breed differences in milk composition, especially milk fat and protein, have been the basis for part of the premium payments that dairy producers have received for the quality of the milk they produce. Note that lactose content is fairly constant among breeds, milk fat varies extensively (Jersey and Guernsey are highest and Holstein is lowest), and protein varies somewhat among breeds.


Milk composition also varies substantially among individuals of the same breed. For example, from the image at right you can see that milk fat in Jerseys, while averaging about 5.5%, can range from less than 4% to greater than 7% for individual cows.

Study Question: Can a Holstein cow produce milk with as high a milk fat % as a Jersey cow?


Differences in milk composition also occur among strains or breeds of other mammals. As an example, milk composition of a typical American breed of pig (Yorkshire) and the Chinese Meishan breed of pigs is given below. These animals were fed the same feed and raised under the same environment.

Study Question: What differences in milk composition do you find among these two swine breeds?

Day of Lactation
 
0
1
7
21
Lactose (mg/ml)
Meishan
19.9
31.7
43.5
51.4
Yorkshire
30.4
38.1
47.1
49.6
Fat (%)
Meishan
7.4
10.9
10.0
7.78
Yorkshire
5.5
7.8
7.8
6.58
Protein (mg/ml)
Meishan
154.4
28.4
28.4
28.9
Yorkshire
139.7
58.8
35.7
36.5

[Data from Zou et al. 1992 ]

Breed Variability
Milk Composition & Synthesis
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