l. In mating a bull (7015) being a carrier of the porphyrin gene (Dr) to ten unrelated heifers, 8 calves were produced. These are all clinically normal. This is regarded as evidence that the inherited character is not dominant.
2. In mating bull 7015 (Dr) to his own daughters the results are
(a) 7019 had 3 normal calves. 7019 is therefore probably a DD
(b) 7021 had 2 calves. The first calf suffered from congenital porphyrinuria. The second calf is normal. She is therefore a carrier (Dr).
(c) 7022 had 3 calves, two are normal, the 3rd is a case of pink tooth. She is therefore undoubtedly a carrier (Dr).
(d) 7023 is an affected heifer (rr). She had one calf, also an affected case.
(c) 7024 is not a daughter, but related to bull 7015 through her own sire. She had one affected calf, 7023, and one normal calf 7029. This normal calf was mated to her own father (bull 7015) and a normal calf was produced. 7024 is therefore a carrier (Dr) and her calf 7029 may be either completely normal (DD) or a carrier (Dr).
These results indicate that bovine congenital porphyrinuria is a recessive character.
3. The recessive character was probably introduced into the Swaziland herd by bull No. 2 used by the owner. This bull was apparently never used on his own daughters and as the character is not dominant, no cases were seen in that herd during the time of his reign. The 3rd bull No. 7015 was bred out of the same herd as bull No. 2. They were therefore related and probably inherited the recessive character from the same sire, the bull Royal Regent. Bull 7015 was therefore mated to related females and within a relatively short time, 13 cases of the condition were observed in that herd, whilst the bull 7015 was being used as a sire.
4. When the Friesland bull Kamnatie Charles was inbred to his own daughters two cases of the condition were observed. This bull is therefore a carrier (Dr). He is related to a grade Friesland cow, suffering from the condition (rr) (Cedara Case).