40 SCIENCE AND PRACTICE OF DAIRYING. 



15. The Age of Cows. The milk-yielding capacity of good cows 

 increases, year by year, within certain limits, from the first lacta- 

 tion period, and from then decreases with increasing age. It may 

 be assumed that, generally speaking, the milk-yielding capacity of a 

 cow increases up to her eighth year. The age up to which it pays 

 to retain a cow differs in the case of individual animals and different 

 breeds, and depends also on the food and treatment of the animal. 



In what way the chemical composition of the milk of single cows 

 varies from year to year with the increase of age has not so far been 

 closely investigated. According to experiments made in Kleinhof-Tapiau, 

 it would appear that in the case of cows which exhibited with increase of 

 age a decrease in their yearly yield of milk, it was found that the per- 

 centage of total solids decreased, and to a still greater degree that of the 

 fat. In these experiments the youngest cow yielded a milk containing 

 solids richest in fat. 



16. The Effect of Bulling. The influence which bulling exerts 

 on the secretion of milk, during the period of lactation, varies very 

 much according to the individuality of the cow and her general 

 state. In many cows the bulling passes without a trace of effect, 

 and in others it has been noticed that the quantity of milk decreases 

 considerably, the specific gravity decreases, the percentage of fat is 

 largely reduced, often to 1 per cent, the milk becomes coagulated 

 on heating, and is not acted upon by rennet. These changes, how- 

 ever, even when they have been most marked, always disappear 

 quickly, usually entirely after two days. 



It has been noticed that cows, which during bulling yield a milk poor in 

 fat, directly afterwards yield a milk unusually rich in fat, so that, in this 

 way, the early decrease in fat is compensated for by the subsequent increase. 

 The earlier widespread opinion, that the spaying of cows always exercised 

 a favourable influence on the secretion of milk and on the capacity for 

 taking on fat, has proved itself unreliable. Careful investigations carried 

 out on this subject have shown that spaying, even in the case of selected 

 cows, is not to be recommended, if care be taken to render them valuable 

 by good feeding without any operation. Spaying is only to be recom- 

 mended in the case of cows suffering from nymphemania (constantly in 

 heat). 



17. The Working of Milk Cows. In very many districts in some 

 countries milk cows are used for working purposes, and the result 

 is naturally enough a distinct decrease in their milk yield. The 



