Roberts: Polydactylism in Cattle 



85 



A GRADE HOLSTEIN COW WHICH HAS THREE TOES ON EACH FOOT 



The mating of a normal bull to a polydactylous cow having three toes on each foot produced a 

 female possessing the same condition. The latter female mated to a normal, unrelated bull has 

 produced three male calves all of which were polydactylous. The inheritance of the abnormality 

 in this case is outlined in the diagram below. (Fig. 27.) 



smaller than those on the hind 

 feet. In each case the third toe 

 is on the inside. This would 

 mean that the extra toe is 

 probably a development of 

 the I or II digit, and probably 

 the II. 



In poultry, guinea-pigs and 

 man, the expression is variable. 

 Sometimes it is dominant and 

 at other times normal individ- 

 uals produce polydactylous 

 offspring. Also many other 

 factors seem to influence its 

 expression. In this case in 

 cattle it is obviously domi- 

 nant. 



<D 



N > normal 



P ; polydactyJous 



(t> 





Inherltanca of polj-dottyll »m in catil* 



Fig. 28 



