Sheehy — Average Percentage of Fat in a Coivs Milk. 557 



(4) There is a great increase in milk and total fat yields when the cows go 

 on the grass. The fat percentage is not affected till a few weeks later, when 

 it drops considerably, and shows much greater daily variations than before. 



(5) After the disappearance of this disturbance, the milk and total fat 

 gradually decrease and the percentage fat gradually increases. 



(ft) A clay or two after the removal from the field to the house, there is 

 another increased variation in fat percentage. 



(7) The curve for cow 159 shows that there is a very high fat percentage, 

 with an increased variation, during the six weeks at the end of the lactation 

 period and during the first three or four weeks of a new lactation period. 

 This is known to be general among cows. 



Assuming that the twelve cows whose milk was investigated behaved in a 

 fashion normal to cows generally, it may be concluded that there are four 

 periods in a lactation when the percentage of butter fat in the milk may 

 diverge so seriously from the average for the whole lactation that they should 

 be avoided by a sampler if a fair average for a whole lactation is to be based 

 upon a few samples. These periods are :- — 



(1) The; first three or four weeks of a lactation. 



(2) The last five or six weeks of a normal lactation. 



(3) A peiiod of about six weeks after the cows go on to the grass from 

 the house, iu the case of cows entirely house-fed during the winter and spring. 



(4) The first three weeks after the cows- go into the house in autumn. 

 In this connexion it is interesting to compare the 'above w r ith the diagram IV 

 taken from Professor Berry's Eeport. 1 The cows represented were put on to 

 the pasture in May and housed again in October. 



April 



Cow No.7. 



july aug. sept. oct. novt 

 Lactation Period in Months 

 — CowNo.17. COW No. 6.- 



Diasram IV. 



1 The Yield and Composition of Cows' Milk during Lactation, Bulletin No. 76., The 

 West of Scotland Agricultural College. 



