Masters Theses

Date of Award

12-1966

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Husbandry

Major Professor

H. J. Smith

Committee Members

E. R. Lidvall, Lewis Dickson

Abstract

Agriculture is entering an age where, to survive, the Tennessee farmer must either purchase more land or improve production on the land he has. Most of the time it is more economical to improve one's production per acre or per animal. One method of accomplishing greater production is through selection of superior producing animals. Selection has been done for centuries through visual observation. To justify their existence as a group, breeders of registered sheep must produce a type of sheep superior to those in the hands of the commercial producers they serve. This superiority must be expressed in demonstrated ability to increase the quantity and quality of the products the operator has for sale, or in increased efficiency of production. Purebred sheep flocks have been instrumental in establishing the type of commercial lamb which has been produced for several decades. Successful purebred breeders in the future must not only raise sheep of an acceptable breed-type or character, but they also must produce individuals of an excellent known productive ability. These seed stock producers must gear their breeding and selection programs on performance indexes which include a combination of characters such as the pounds of lamb and wool produced per ewe and the quality of the carcass produced, as well as on an acceptable breed type. Growth rate and other traits of sheep are controlled by both genetic and environmental factors. Heritability estimates for genetic effects have been established as approximately 25 per cent for weaning weight, 35 per cent for rate of gain, and 40 per cent for yearling body weight. Therefore, under desirable management conditions, relatively rapid progress could be made in selection for improved gaining ability within each flock, among various types within breeds, or in the existing breeds of sheep which are prevalent today. By utilizing selection indexes for rigid culling and replacement ewe selection over a five-year span, commercial sheep producers in Ohio have increased their 120-day lamb weights by 30 pounds. Performance tested flocks in the state of Wisconsin have shown 16 pounds increase in terms of lamb produced per ewe at four months of age. By eliminating the poor performing ewes in both commercial as well as purebred flocks, the total productivity of the Tennessee sheep industry can be increased. The improvement in lamb production can occur and at the same time, the type of sheep can be produced which will meet the approval of veteran sheep breeders. Gains through breeding are often slower of achievement and less spectacular than gains through improvements in feeding and management. However, genetic gains are permanent, and since the inherited capacities of animals to produce place a ceiling on the production per individual, genetic improvement must accompany improvements in other phases of production if continued progress is to be made. Estimating the gains which might be achieved by improving the inherited abilities of sheep to produce is not easy. Among other reasons, it is difficult to estimate the net profit resulting from a given genetic change because the benefits of almost any such change are not obtained without some increase in cost. For example, if producers were suddenly presented with ewes all of which consistently produced twins, they would not realize the advantages of this increased potential unless management improved so that these twins had a good chance of survival, nor could they carry the larger number of lambs to market without some increase in feed. Nevertheless, such a genetic change would undoubtedly lead to an increase in efficiency and in profit in almost all sheep enterprises. Likewise, increased rate of gain to weaning or wool production would not be achieved solely by using genetically superior stock. Some additional feed would be required, but raising the more productive individuals would be expected to increase net income. The problem of an objective measure for selection among potential breeding animals, where more than one trait, or character is to be considered, is always faced by breeders. It has been shown that selection is more effective when based on total score or index, combining and properly weighting the several traits under consideration, than it is for single traits or for several traits with independent culling levels. The purposes of this study were (1) to compare the performance of ewes and lambs from three different breeds of sheep and (2) to evaluate the effects of various factors including year, age of dam, type of birth and rearing, sex of lamb, month of birth, and sire on birth weight, weaning weight, average daily gain, condition grade, type score, and 120-day weight of lambs.

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