CHAPTEE VI. 



Duration OF Yield in Milk Cows. 

 Cows dry up their Yield to C07itinue their Breeding Power. 



Guenon, in his work on the "Escutcheon," has laid 

 down fixed rules as to the time of drying, or duration of 

 yield ; but has not explained any point on the subject, nor 

 established any basis for such rules. Hence the rules are 

 merely simple statements. The mammary blood that sup- 

 plies the milk glands at one season, and the embryo at 

 another, is correctly the breeding blood, because it is 

 specially provided to enable cows to nourish their progeny 

 during the several stages of breeding. The mammary 

 arteries are called by that name because they convey the 

 breeding blood to the udder, which has teats for suckling. 

 There are two sets of breeding arteries, both of which are 

 provided for conveying nourishment to the progeny ; but 

 the breeding arteries are not naturally provided for nour- 

 ishing the system of the cow. 



The Ovarian and Uterine arteries are the mammary 

 trunk tubes. One set of these arteries conveys blood to 

 the embryo until calving time, while the other set comes 

 into use at once, after calving — or a little while before — to 

 supply the calf with milk, by supplying the udder with 

 blood to form it. Only one set of breeding arteries is natur- 

 ally in use at one time ; as the demand for blood to nourish 

 the embryo is arrested by calving, on the removal of the 

 placenta and embryo together ; the breeding blood which 

 supplies the embryo through the placental circulation, 

 previous to its birth and breathing, being conveyed in the 



