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Arizona Agricultural Experiment Station
Abstract
The inheritance of a dwarf anomaly, known to occur frequently in Hereford cattle, was studied. Four breeding tests were conducted to determine the mode of inheritance. The results of these tests indicated that the dwarfism is attributable to an autosomal recessive gene with complete penetrance.
In the first test, ninety heterozygous x heterozygous matings produced normal and dwarf offspring in a phenotypic ratio of 3:1. A sex ratio of 1:1 was observed in the dwarf population studied.
Test II was comprised of five dwarf x dwarf matings. The resulting progeny were dwarfs, but the abnormal characteristics were no more extreme than those exhibited by a number of dwarf offspring from heterozygous x heterozygous matings.
In Test III, a limited number of heterozygous cows were mated with dwarf bulls (six matings). The progeny appeared in a normal-dwarf phenotypic ratio of about 1:1.
A dwarf sire was used on females of undetermined genotype in Test IV (seven matings). Dwarfism had not been recognized in the herd from which the females were obtained. The progeny that survived were normal. Stillbirths or early, postnatal mortality precluded the substantiation of a few phenotypic classifications. The need for positive methods of identifying the dwarf phenotype in the event of early death losses was pointed out.
1 The authors are grateful for the data and the livestock contributed by cooperating breeders, for the financial aid and the records supplied by the American Hereford Association, and for the dwarf animals obtained by Mr. Dan W. Clarke of Tucson, Arizona. Thanks are extended to Drs. W. J. Pistor, V. H. Fisher, and R. E. Reed for veterinary assistance and to Mr. T. P. Jardine for the pedigree studies.
Arizona Agricultural Experiment Station Technical Paper No. 346.
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