any change in the quality or quantity of the feed will result in a change 

 in the milk produced per unit of time. The milk production function for 

 the purposes of this study is a herd function. It was assumed that the 

 herd composition is homogeneous and that changes in feed inputs can 

 be reflected in output for the herd much as they would be for the 

 individual cow. The assumptions used in this study to control the non- 

 feed and feed factors are outlined in the following sections. 



Cow Al>ility 



The ability of a cow or a herd of cows to convert the combinations 

 of forage and grain into milk is determined by 2 closely related factors: 

 (1) the inherent milk producing ability of the cow and (2) the ability 

 of the cow to consume large quantities of forage. To overcome varia- 

 tions that occur between cows, it was assumed that all cows had a high 

 inherent ability and could consume large amovints of forage. 



Stage of Lactation 



The freshing pattern of a herd of dairy cows has a great influence 

 upon the seasonal milk produced; therefore, the assumption was made 

 that the freshing pattern was randomly distributed throughout the 

 year and that any cows added to the herd would not disturb this 

 distribution. 



Other Factors 



There are many other factors that affect the quantity of milk pro- 

 duced by a cow or a herd of cows such as cow age, body weight, and 

 temperature. In this study it was assumed that body weight did not 

 change. This implied that (1) the total amounts of nutrients consumed 

 by the cow would be used in the production of milk, and (2) that the 

 age of the cows was randomly distributed. The same number of cows, 

 therefore, would be replaced every year; thus, the milk production sur- 

 face was not affected. Further, it was assumed that all other variables, 

 such as cow temperatures, were constant. 



Forage Input 



Forage is the major input in the production of milk; therefore, a 

 complete understanding of the meaning of forage as used in this study 

 is necessary. It should be understood that quality and quantity of forage 

 produced per acre by date of cut are inversely related. 



In addition to the quality and quantity relation, nutrients are 

 lost through rain damage; thus, there are 2 types of forage available 

 to produce milk: (1) forage undamaged by rain and (2) forage damaged 

 by rain. The difference between the 2 types of forage is that for each 

 and every date of cut, the percentage of digestible dry matter of rain- 

 damaged forage will be less than if no rain damage occurred. When 

 rain-damaged forage is fed, nutrient intake will drop unless more forage 

 is consumed or grain consumption is increased. 



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