THE INCUBATOR-BROODER METHOD OF RAISING GROUSE 



479 



likely to result. If the eggs have not lost sufficient moisture at a given point in incubation, 

 it is necessary to reduce the humidity and increase the ventilation to permit more rapid dry- 

 ing through the shells. In the still-air incubators temperature also is affected by ventilation 

 changes and, thereafter, must be readjusted. 



Although the shell of the grouse egg is almost as thick as a pheasant's, averaging 0.21 mm. 

 it has less pigment and is less opaque. It is wise to candle all newly set eggs on the third day. 

 As pointed out before, those that are infertile may then be identified although not removed 

 and arrangements made immediately to place a different male in the breeding pen in which 

 the eggs were laid. 



Fresh egg 



Inlertile egg, ftlh day 



Fertile egg, .ith day Dead genu after Ith day 



FIGURE 38. APPEARANCE, UNDER THE CAMJLIiNG LAMP. OF FERTILE AND INFERTILE 



EGGS DURING INCUBATION 



A little experience, aided by a careful study of figure 38 will assist the beginner to detect 

 the clear eggs which are infertile. As incubation progresses a live embryo may be identified 

 under the candling lamp as a dark floating spot from which blood vessels radiate. Under 

 normal development, by the 12th day the blood vessels have advanced until they meet at the 

 small end of the egg. Just prior to hatching, the egg will be opaque except for the area occu- 

 pied by the air cell. Once one has become skilled in recognizing these changes, it is helpful 

 to candle the eggs on the 12th day and again on the 21st day, just before shifting them to the 

 hatching compartment. 



The practice of checking weight losses to determine moisture content is also distinctly 

 helpful, for unless a chick hatches clean it is apt to die or be weaker than the rest. Careful 

 experiments at the Center have indicated that grouse eggs hatch best when about 13 per cent 

 of their weight is lost in the first 21 days of incubation. 



The following is a simple formula for determining the percentage of weight loss at hatch- 

 ing time provided the existing rate of moisture loss is maintained. 



WL 

 WE 



X " X 100 = Percentage loss in weight projected to hatching time 



WL = Weight loss at the time of weighing 



WE = Weight of eggs at time of setting 



I = Incubation period (231/^ days for grouse) 



D = Number of days eggs have been incubated at the time of weighing 



