Duration of Yield. 65 



ing over any average quantity of milk, are more or less 

 relaxed in their arteries and udders, the milk glands being 

 relaxed in many instances, from the same influence, name- 

 ly, over-rapid expansion, the degrees of artery relaxa- 

 tion varying in different cows. 



The yield of milk is generally according to the quantity 

 of breeding blood— the supplementary blood that is added 

 to the general circulation, but conveyed in the breeding 

 arteries to the milk glands. The larger this supplemental 

 quantity of breeding blood, the larger the milk glands and 

 udder must be; and the larger the quantity and bulk of milk 

 and the size of the udder, the longer the process of drying 

 will require. The largei- the quantity of blood from which 

 yield is formed, the longer the time required for diverting 

 it towards the embryo ; consequently the period occupied 

 in drying up the yield . will be generally according to the 

 quantity, and the duration of "yield" generally must be 

 according to the size of the udder and the quantity of 

 milk. 



The dry feed of fall and winter rapidly reduces the bulk 

 of yield in cows generally; and of course those yielding 

 least dry first as a rule, because they have a smaller amount 

 of breeding blood. The exceptions to this rule result from 

 weak contractility in the udder supply arteries. Generally 

 the rule will hold, on dry feed or green, that cows yielding 

 the most milk will continue their yield the longest and 

 latest. Remembering the exceptionally long duration of 

 yield in cases where the arteries and urkler are relaxed by 

 engorging degrees ofincrease in food, blood, and yield, as 

 explained in other chapters. 



Duration of yield is generally according to its quantity, 

 the size of the udder of course being according to the 

 quantity of milk it contains. But as the prolongation of 

 yield at the pail by pregnant cows is always in conflict 



