82 THE BREEDING OF ANIMALS 



intermission. The more important conditions which in- 

 fluence the duration of lactation and the amount of milk 

 produced among the domestic animals are food supply, 

 habit, heredity, exercise, climate and nervous excitement. 



76. The food supply. Every mature domestic animal 

 requires a certain minimum amount of food to maintain 

 the ordinary bodily functions. This is called the food 

 of maintenance. The function of milk-giving must be 

 regarded as an additional requirement. The animal, 

 therefore, that is producing milk must consume and 

 assimilate larger quantities of food than one that is dry 

 or not producing milk. It follows that the greater the 

 amount of milk produced, the larger the demands of the 

 lactating animal for food. In an ordinary cow in full 

 milk, the food of maintenance may represent sixty per 

 cent of all the food eaten. In this case forty per cent 

 of the ration is available for milk production. In a 

 heavy-producing cow, the food of maintenance may 

 represent only forty per cent of the whole. In the latter 

 case, as much as sixty per cent of the ration may be utilized 

 for milk production. The greater economy of production 

 in the case of the heavy-producing cows is at once appar- 

 ent. If an insufficient ration is fed to any cow in full 

 milk, the first effect will be to cut down the milk flow. 



77. Habit. The duration of the lactation period is 

 materially influenced by the habit of the cow as deter- 

 mined by man. The lactation period of a cow, which is 

 normally ten months, may be shortened by careless milk- 

 ing or insufficient feeding. The milking function may be 

 so stimulated by careful and thorough milking and intelli- 

 gent feeding that the daily quantity of milk may be 

 increased and the period of lactation lengthened. 



78. Heredity. The capacity to give milk in abundance 



