PRINCIPLES OF LIVESTOCK BREEDING. 31 



Another interesting pair of factors is found in the red and white of 

 the Shorthorns. In this case neither is dominant. The heterozygous 

 animals have a mixture of red and white, the familiar roan pattern. 

 The roan is thus an unfixable color. Roan by roan produces only 

 about 50 per cent roan calves, the rest being equally divided between 

 red and white. Practically 100 per cent roan can be obtained by 

 breeding a white bull with red cows, or the reverse. The factor 

 which removes the color from the hair of roans and whites is inherited 

 independently of the kind of color. Thus, when a white Shorthorn 

 bull is bred with black Aberdeen- Angus or Galloway cattle, the black 

 of the latter is dominant over the red factor which is present in white 

 Shorthorns as well as red ones, while the white factor of the Shorthorn 

 is imperfectly dominant over the solid color of the Aberdeen Angus or 

 Galloway. The result is a blue roan. When such blue roans are 

 crossed together, blacks, blue roans, whites with black ears, reds, red 

 roans, and whites with red ears, are all produced if enough calves 

 are born. All but the last class were found among 21 calves pro- 

 duced in such an experiment at the Iowa agricultural experiment 

 station. 



Other colors in cattle have not been worked out so satisfactorily. 

 There appears, however, to be an imperfectly dominant dilution 

 factor which reduces black to dun color and red to fawn. The white 

 patterns of many breeds are inherited independently of their colors 

 and are, at least to some extent, dominant. The white face of the 

 Hereford is thus transmitted to nearly all the calves in the first 

 generation of a cross whether the rest of the coat is black or red, and 

 is a useful "trade-mark " for the recognition of Hereford grades in the 

 market. Grades of the dairy breeds are usually recognized by show- 

 ing traces of the dilute color of Jerseys or Guernseys or the large, 

 irregular, white areas of Ayrshires, Holstein-Friesian, and many 

 Guernseys. 



COLORS OF HORSES. 



The colors of horses have been worked out in much detail. The 

 power to develop black (factor H) seen in bays, blacks, duns, etc., is 

 dominant over its absence, as seen in chestnuts (factor K). Bays (B) 

 differ from blacks (b) by an independent factor which may or may not 

 be transmitted by chestnuts. The dilute colored duns, creams, and 

 mouse-colored horses differ from bays, chestnuts, and blacks, respec- 

 tively, by a third dominant factor (factor D and d). Three other 

 independent pairs of factors determine between the roan (R), gray 

 (60, and piebald (S) patterns and their absence (r, g, and s). Since 

 a chestnut horse is recessive in all essential factors (hhddrrggss) , he or 

 she can produce only one kind of reproductive cell (Jidrgs), and two 

 chestnuts, whatever their ancestry, can produce only chestnut 

 foals. 



