Masters Theses

Date of Award

12-1967

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Husbandry

Major Professor

H. V. Shirley

Abstract

The increase in egg production in the last 20 to 30 years has been due to improved nutrition, management and the use of hybrid chickens; crossbreds, strain crosses, inorosses and in-crossbreds. The commercial poultryman, as a rule, no longer produces his own replacement stock from his existing flock. He generally obtains new stock each year from the commercial breeders' outlets. It is generally thought that if hybrids produced by these breeding systems were used to produce replacement pullets there would be a significant reduction in performance and an increase in variation. It is assumed that hybrid vigor expressed by these stocks would be reduced in the advanced generation as a result of the segregation and recombinations of the favorable genes or gene combinations. Since the advent of chicken hybrids, it has been recommended to the poultryman that he purchase his replacement stock from the commercial breeder on a yearly basis. This recommendation is based in part on the many population experiments exemplifying the increased variability and decrease in the mean in a segregating generation. The recommendation is also based, to a great extent, on experiments with hybrid corn and a statement by Wright (1922) that, "a randombred stock derived from inbred families will have 1/nth less superiority over its inbred ancestry than the first cross or a random-tred stock from which the inbred families might have been derived without selection." Also, Falconer, (1960) gives a good discussion by use of the Hardy-Weinberg formula of the reduced heterosis expressed in the F2 generation. His conclusion is that heterosis in the F2 generation can only be one half that shown in the F1 generation. The experiments with corn and Wright's work both deal with inbred lines used in the breeding system. However, not all commercial poultry breeders, today, employ inbred lines to produce their product. This experiment is designed to ascertain if the reduction, if any, in the performance of an advanced generation produced from chicken hybrids is significant.

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