INFLUENCE OF DISEASE UPON MILK 113 



BLOOD IN MILK 



& mixture of blood with the milk may occur as a 

 result of traumatisms of the udder, such as kicking, hook- 

 ing or treading, which cause hemorrhages or blood infil- 

 trations into the udder tissue. The pulling or dragging 

 to which a greatly distended udder is subjected when the 

 cow walks may cause a tearing of the udder tissue which 

 will permit the mixing of blood with the milk. When 

 large blood vessels have been injured the milk is colored 

 diffusely red. But when small vessels are torn or rup- 

 tured, which is more often the case, only small streaks of 

 blood are observed which disappear when the milk is 

 shaken and do not discolor it. When such milk is centri- 

 f ugalized, the sediment shows a red color which, on micro- 

 scopic examination, is found to be due to the presence 

 of red-blood cells. Blood is observed in the colostrum 

 or milk during the first week following parturition in 

 those cases in which the udder is intensely hypersemic, 

 resulting in a diapedesis of red-blood cells. 



(EDEMA OF THE UDDER 



Sometimes, especially in heifers with the first calf, 

 the udder becomes very much swollen and oedematous 

 shortly before parturition. The swelling is not hot, nor 

 is it painful unless the skin is intensely stretched; it 

 disappears a few days after parturition. Usually, no 

 essential changes are observed in the milk. It is probable 

 that some of the serous transudate is mixed with the 

 milk, but nothing definite is known on this point. Some- 

 times the milk contains blood. Generally, the oedema 

 has disappeared by the time the colostral stage is passed. 

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