172 



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The Journal of Heredity 



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24 30 36 42 48 54 60 66 72 78 



90 96 102 108 IM 70 126 132 138 144 150 156 1&2 Ifcg 174 ISO 186 192 198 204 



.•\GE OF DAMS IN MONTHS 



FREQUENCY CURVE FOR DAMS 



Figure 13. The percentage of young born by dams of various ages is shown in this chart. 

 The age of the dams is computed for six-months periods, and the upper age limit of these groups 

 is shown. That is, all the dams 24 months and under are considered 24 months old, those between 

 24 and thirty months of age, as 30 months old, etc. It is evident that much the greater number 

 of calves are born by very young cows, the quality of whose offspring cannot be known. (See text, 

 p. 171.) 



