Factors affecting Composition of Milk:-

Major Factors:-
Species:- The growth habits and body requirements of different species is different so they differ in their milk composition. E.g. human infant takes 6 months to double their weight because human milk contains 1.9% protein, whereas cattle infant takes 50 days (3.5% protein), rabbit infant takes 7-10 days(9% protein)

Breed:- Some breed producing the largest amount of milk but milk of a lower fat%. E.g. American cow producing largest amount of milk but fat % of the milk is low while the Indian cow yielding low amount of milk but the fat% of the milk is high. 
Individuality:- It is the tendency of animal body to produce milk of constant composition.


Feed:- If a particular substance is deficient in diet, body reserve is used to synthesis milk and if deficiency continues, milk production is decreased and ultimately animal ceases to produce milk.

Minor factors:-
Season:- The % of both fat & SNF show slight variation during the course of year.
Age:- As the animal advances in age there is a progressive fall in the fat content of milk and total quantity of milk.
Condition of cow at calving:- If the cow is in good physical health when calving, it will yield milk of a higher fat% than  it would if its condition was poor.
Stage of lactation:- Colostrum contains more minerals, total protein and less lactose than milk drawn 2 or 3 days later. The fat content may be higher or lower than normal milk. In later stage of lactation, the milk becomes saltish because of the high chloride content.
Interval of milking time:- The longer the interval, the greater the quantity of milk and lower the fat test.
Procedure of milking:- Variations in milking procedure also affects fat contents of milk. First drawn milk or foremilk is very poor in fat content and last drawn milk or stripping is very rich in fat content.