60 



rate of lay, hens were exposed to 14 hr of light by the use of supple- 

 mental incandescent lights in the morning and evening. Ail eggs 

 produced by hens consuming unlabeled IGR's were destroyed and hens were 

 destroyed after the experiments were terminated. 

 Calculation of Hen-Day Egg Production and Average Daily Feed Consumption 



The term hen-day implies that during the time period over which the 

 calculations for production or consumption have been made, daily hen 

 mortality has been taken into consideration. In order to calculate on 

 a hen-day basis, daily mortality records were kept. 



Hen-days are calculated by multiplying the number of hens on hand 

 by the number of days in the designated time period. This is simple if 

 no mortality occurs. For example, 10 hens during a 7 _ day period consti- 

 tute 70 hen-days. However, if one hen died on day 5, the number of hen- 

 days becomes nine hens times 7 days plus one hen times 4 days for a total 

 of 67 hen-days. Whether or not the day on which hen mortality occurs is 

 to be counted in the calculations for hen-days should be decided in 

 advance and adhered to. 



Hen-day production is therefore the number of eggs laid during a 

 time period divided by the number of hen-days calculated for the same 

 time period. The quotient is multiplied by 100 since hen-day production 

 is expressed as a per cent. 



Consumption figures are usually expressed as the amount of feed 

 consumed per bird per time period, e.g. 114 g per bird per day, and 

 not as hen-day consumption. However, total hen-days as well as total 

 feed consumption must be known in order to calculate the average daily 

 consumption per bird. Total feed consumption is all the feed consumed 



