Oharaeteristics of Abortion. 223 



portion of the cows that abort, in numbers of instances, 

 being " new " cows, which are known to be about loo per 

 cent more liable to abort, than cows that are home-raised. 

 Numbers of new cows that have their arteries relaxed, con- 

 sequently abort ; while on the exempted farms there are 

 probably fewer new cows in the exempted herds, and the 

 cows may not be quite so fully fed, or the quality of the 

 food may be somewhat different. Even a slight difference 

 in quantity or quality of feed, or of increase in blood, be- 

 ing quite sufficient* to exempt the intermitted herds or 

 farms, from such relaxation of the arteries as occurs in af- 

 fected herds. In such cases, it is the last ounce, even a 

 small actual increase in blood that engorges ; the last grain 

 turns the scale ; a slight increase in degree of engorgement 

 beyond a certain extent, relaxes the walls of the udder- 

 supply arteries, that are already much distended. 



Home-raised cows are frequently large in their yield ; 

 but they are less liable to abortion, because there is no 

 rapid increase or change in their supply of feed, as a rule. 

 Some few may eat more feed when fed together with new 

 cows, and so increase the quantity of their blood so far, if 

 only 5 to lo per cent, as to over-strain and relax their dis- 

 tended arteries, and afterwards abort from such relaxation. 



Numbers of herds of large-yielding cows are, however, 

 exempt, because they do not have their feed, or blood, or 

 udder-supply artery size rapidly or rashly increased at any 

 time, the rule being that changes in their feed are only 

 gradually made. 



Heifers are as liable to increase their blood from increase 

 of feed, and to engorge their udder-supply arteries, as 

 cows. But heifers that are treated like exempted cows do 

 not abort, while heifers that are new to the full-feeding, 

 being brought in with new or stranger cows, and having 



* See diagrams, Plate VI. 



