Abortion in Cows. 207 



from 20 to 100 or 120 per cent in a few weeks or months, 

 as happens in various cows in cheese-factory and milk 

 herds, in various localities, the size of the udder is evi- 

 dently increased to a corresponding extent, the milk-glands 

 being similarly enlarged. 



The artery blood from which milk is formed being con- 

 veyed to the milk-glands of the udder by the udder-supply 

 arteries, the tubular size of these arteries is increased to 

 the same extent or percentage that the size of the udder 

 and extent of yield are increased. So that when the yield 

 of cows is increased as much as from 25 to 100 per cent, 

 as occurs in many cases in cheese-dairy districts — the in- 

 crease probably reaching as high as 120 to 140 per cent in 

 some extreme and exceptional cases — the increase of d/oo^f 

 in the arteries supplying the udder is at the same great 

 rate ; and the tubular size of the udder-supply arteries is 

 thus increased by blood engorgement to the extent of from 

 25 to 100 per cent, within a single grass season of eight or 

 ten weeks, in numbers of cows. So the mammary arte- 

 ries of some cows are expanded to 120 or more per cent 

 in excess of their previous size within fourteen months, cwr 

 during the abundance of succulent grass growth, in only 

 two summers, in numbers of instances, when the cows ob- 

 tain a great and rapid increase of feed. 



The danger of relaxation in the udder-supply arteries, 

 and of abortion in dairy cows, is according to the rate or 

 rapidity at which the artery walls are thinned down,* 

 which, as its consequence, is according to rapidity of in- 

 crease in feed, and blood made from it, in a given length 

 of time. For instance, when a cow's yield is increased 

 50 per cent in only three months, the danger of relaxing 

 the artery walls by the pressure of engorgement is more 

 than three times as great as when an equal increase is made 



* A diagram phowing certain degrees of artery expansion is given at tlio 

 end of this chapter. 



