Evaluation of the X-Ray Method of Detecting Animals Heterozygous for Snorter Dwarfism

Dwarfism in beef cattle: Diagnosis and control

“…In America, the development of a system for confirmatory diagnosis of both homozygous recessive and heterozygous carrier animals has received much attention. Special tests developed have included the profiIometer which reveals differences in head conformation Gregory and Brown, 1952;Dinkel and Gregory, 1965), variations in blood plasma cholesterol levels (Fransen and Andrews, 1958), cardiac radiography and electrocardiography (Dinkel et al, 1960) and the use of bone radiography (Emmerson and Hazel, 1956;High et al, 1959). Chromosome analysis of a snorter dwarf bull presented for examination at Massey University showed a normal male karyotype (Bruere, ununpublished data).…”

“…A detailed description of these bony lesions and the skeleton in general of dwarf calves has been given by Tyler et al (1957). High et al (1959) emphasized that, while radiographic techniques were very reliable for confirming the diagnosis of a homozygous recessive dwarf calf, their accuracy in detecting heterozygous carrier animals was very limited. Certain radiological features could be seen in some heterozygous animals, but these showed a wide range of variability.…”

“…Of these tests, radiography would appear to be the most useful means of confirming a diagnosis of dwarfism. A radiographic survey was conducted on 1,500 Hereford and Aberdeen Angus cattle by High et al (1959). Subsequent mating of gene carrying animals from the survey showed that, in the homozygouS recessive (tnte dwarf), radiographic features are completely diagnostic.…”