78 



VARIATION OF FAT IN MILK AND CREAM 



The practical lesson to be drawn from this is that milking 

 should be done efficiently and completely. 



6. Age of Cow. As already pointed out, the richness of a 

 cow's milk is very largely determined by heredity. She will not 

 produce rich milk during one lactation period and poor milk 

 during another. However, age has its influence. Normally 

 there is a marked increase, from year to year, in the quantity of 

 milk given, with a tendency to a slight increase in the fat-content, 

 until a cow reaches maturity. Then, in the ordinary course of 

 events, we may look for a gradual decline. The following is 

 quoted from Eckles, whose investigations were both extensive 

 and thorough: " On the average, a well-grown two-year-old 

 may be expected to produce 70 per cent, a three-year old 80 

 per cent and a four-year old 90 per cent of the milk and fat that 

 she will produce when mature." " The average fat-content 

 remains practically constant from year to year, except that after 

 the cow is eight or nine years old the percentage of fat always 

 declines slowly and gradually with advancing years." 



7. Advance in Lactation. This is a factor that materially 

 influences both the quantity of milk produced and its fat-content. 

 When a cow freshens she will probably, if in reasonably good 

 condition, produce milk with a slightly higher per cent of fat in it 

 than there will be a little later. With this exception the quan- 

 tity of milk produced and the per cent of fat in it usually remain 

 fairly constant during the first three or four months, after which 

 there is a gradual decline in the quantity of milk produced and a 

 steady increase in its richness. But cows differ very widely in 

 the rate of increase in the fat-content of their milk as they 

 advance in their lactation period. The following table gives the 



