204 Cattle Problems. 



its flow into the placental vessels is consequently abruptly 

 reduced, as the more or less drained and empty condition 

 of the placental vessels sufficiently proves.* 



In most cows that abort from mammary artery engorge- 

 ment, and embryo starvation, the engorged condition of 

 the arteries is continued by the continued excess of blood 

 supply that maintains the large yield ; the relaxed con- 

 dition of the artery walls becoming fixed by long-continued 

 engorgement. A long time must be required to repair 

 the injury to the artery walls, and restore contractile 

 power when the relaxation is considerable or severe, be- 

 cause, as in the case of the udder, expansion distends them 

 to scores per cent beyond the natural size, the blood ves- 

 sels being more widely separated in a much larger area of 

 wall, the proportion of blood supply to area being very 

 much reduced. In like manner the rapid doubling of a 

 cow's yield increases the area of artery wall over 40 per 

 cent, correspondingly reducing the proportion of blood- 

 vessels and blood in the surface area of the artery walls. 

 So the rate of nutrition in the artery walls is reduced as 

 the size of the arteries is increased by engorgement, thus 

 causing chronic relaxation, and postponing or entirely pre- 

 venting the recovery of artery contraction in many abort- 

 ing cows. It is this chronic relaxation of their mammary 

 arteries wliich destroys breeding power in numbers of deep 

 milkers, and suspends the breeding power in many farrow 

 cows that breed intermittently.f 



Tlie starvation of the embryos previous to abortion is 

 proved by the evidence: — 



1. The fact that nearly all the embryos arc dead when 

 aborted proves arrest of nutrition, and 'consequent embryo 

 death previous to abortion, 



2. Several special A\si(tcX\ax\^ by Dr. Halstead, and care- 



*See Dr. Dalton's Eeport to New York State Agricultural Society, Albany, 

 1868. 

 tSeo chapter ou Farrow Cows. 



