Duration of Yield. 61 



This is the probable reason why certain cows of large yield 

 are shy breeders, or breed only intermittently, or in some 

 cases, entirely fail to breed ; the ovarian s)-stem being too 

 scantily supplied with blood and heat, by reason of so large a 

 proportion of the blood flowing to the udder instead of the 

 ovaries. A majority of dairy cows do breed, however, 

 though their calves are generally small, from insufficient 

 nourishment, during their embryonic growth. 



Soon after impregnation, the ovarian and uterine artery 

 s)-stems are again brought into use to suppl}- the embryo 

 calf with blood nourishment, through the umbilical cord 

 and the placenta, or special breeding circulation, thus 

 enabling cows to breed by supplying the blood naturally 

 produced for this function. From this time forward there 

 is a two-fold demand for the satne blood, or a considera- 

 ble and daily increasing proportion of it. Naturally it 

 is required by the embryo calf in daily increasing quanti- 

 ty to form and enlarge its growth. Commercially, or for 

 other reasons, it is demanded at the udder glands to sup- 

 ply the ingredients of milk. So, milking at the udder re- 

 tards impregnation, leads to the breeding of small calves, 

 and sets up a conflicting demand for the blood that alone 

 can be spared after the system of the cow is replenished. 

 On one hand this provision of blood for breeding, natur- 

 ally is required by the embryo; on the other, it is demand- 

 ed at the udder to form milk for domestic and commercial 

 uses. 



The embryo necessarily requires a daily increasing sup- 

 ply of blood, according to its increasing size, and to add 

 thereto by accretion or growth, this increased demand and 

 supply going on, the c<j^ feeling the hunger of the embr}0 

 through their connected nerves, and supplying its demand, 

 until the hunger be satisfied, and the process of feeling 

 and satisfying, or rather endeavoring to satisfy the natu- 

 ral hunger of the progeny, is repeated and continued until 



