Masters Theses

Date of Award

8-1962

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Husbandry

Major Professor

R. J. Cooper

Committee Members

H. J. Smith, C. S. Hobbs

Abstract

Several types of dwarfism have been recognized In beef cattle but none has, to date proposed an economic problem to the beef cattle Industry with the exception of the "Snorter" type. The potential production of Snorter dwarf calves has made the problem of prime Importance to the individual breeder.

Probably the greatest loss has occurred through the decrease In value of purebred animals which are not guaranteed to be free of the dwarf gene. Purebred and commercial producers are skeptical of animals which have a possibility of being a carrier of the Snorter dwarf gene because of the monetary loss due to the production of dwarf calves. These calves often die at birth or shortly after. Those which live have a shorter life expectancy than normal. They are characterized by labored breathing, slow growth rate, protruding, bulging eyes, and uncoordinated movements. Their bodies are extremely blocky and low set on short, heavy-boned legs which are often bowed. With increasing age the Snorter dwarf develops a "potbelly" and is exceptionally susceptible to bloat.

Thus far research Indicates that Snorter dwarfism is Inherited In a simple Mendelian manner, with two recessive autosomal genes being responsible for the phenotypic expression of the anomaly. This being true we may expect to find cattle of three genotypes relative to Snorter dwarfIsm. They are homozygous normal or clean (carrying no gene for Snorter dwarfism), heterozygous or carrier (carrying one gene for this particular type of dwarfism and being phenotypically normal), and homozygous for the dwarf gene (having two Snorter dwarf genes and being a dwarf phenotypically).

At present the most feasible method of detecting carrier animals Is by progeny testing bulls. This Involves mating a bull of unknown genotype to known carrier or dwarf cows or the less common practice of mating the daughters of a bull to a dwarf bull. As would be expected this Is both time consuming and expensive due to the number of progeny which a bull must produce In order to be proven clean (homozygous normal). For example a bull of unknown genotype must produce either five normal calves from dwarf cows or eleven normal calves from carrier cows In order to be proven at the 95 percent level of probability. These numbers are Increased to seven normal calves from dwarf cows and sixteen normal calves from carrier cows to be proven at the 99 percent level of probability.

As a result of the limitations of this method, the frequency of occurrence of dwarf calves Is slow to subside. A Virginia report (Marlowe, 1961) covering the years 1954 through 1959 revealed that 0.35 percent of 5944 Angus calves and 1.41 percent of 6291 Hereford calves born in a number of herds In Virginia were dwarfs. During this six year period the percentages of dwarfs Increased slightly In Angus herds and decreased slightly In Hereford herds.

Most of the work done to date has Involved studying various blood characteristics, physiological responses, body measurements and radiographs of various regions of the body. Recently a similarity has been observed between the Snorter dwarf and human patients with Hurler's syndrome, a type of dwarfism characterized by excessive accumulation of acid mucopolysaccharides In certain tissues and In the urine. The purpose of this paper Is to present the body measurement and X-ray data collected at the University of Tennessee from 1959 through 1962 and to present an analysis of the nature of the mucopolysaccharides excreted In the urine of animals homozygous normal and heterozygous for Snorter dwarfism.

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