Document Type

Thesis - Open Access

Award Date

1967

Degree Name

Master of Science (MS)

Department / School

Dairy Science

Abstract

Increased productivity of dairy cattle depends in part upon genetic changes brought about by select ion. Because of the long generation interval and low reproductive rate, genetic improvement in dairy cattle is slow. For this reason, the accuracy and effectiveness of selection of sires is of utmost importance. Selection of sires plays a major role in the genetic improvement of dairy cattle since a sire can leave many more descendants than a female. Consequently, the use of outstanding males is important in the genetic advancement of the dairy cattle population in the upper mid west as well as throughout the world. This effect on genetic improvement in dairy herds needs constant review to promote progress in dairy cattle breeding. It is important that sires in artificial insemination be of genetic value superior to the population average. This is imperative when it is realized that through artificial insemination, a sire can be mated to many more cows than he could be naturally and over a much greater area. However, because fewer sires are needed, the mean breeding value of those sires can be higher than the mean breeding value of the larger group, providing an accurate method of evaluating these sires is exercised. Consideration of DHIA Sire Summary Lists indicates that these sires are being identified and that effective means of improving genetic merit may be available. A sire's value for dairy purposes is dependent on the quality of daughters he leaves. The measure of this is governed almost entirely by the production records of his daughters, which gives information as to their phenotypic value. The phenotype of a daughter can be divided into genotypic and environmental contributions. The corresponding partition of the variance into genotypic and environmental components makes up the problem of heredity versus environment in determining, the worth of an individual. These environmental factors, which weigh heavily on the daughters' producing ability, change from herd to herd. Any change which might take place in feeding and management or differences in season of freshening may effect the producing potential of a sire's daughters. In view of these facts, simple comparison of production levels of various sires' daughters would leave much to be desired, especially if one considers the bias that may also be introduced by selection of records or animals for comparison. Until recently, the daughter-dam comparison technique played an integral part in sire evaluation procedures. However, within the past seven years attention in sire appraisal has shifted to the use of the milk yield of the herdmates of sires' daughters. Two main objectives were believed to be accomplished by using the daughter-dam comparison in the estimation of the sire's breeding value. First, the dam's yield served to correct for any tendencies to use sires on cow groups differing in average genetic merit. Secondly, the dam's production was believed to correct for environmental circumstances. The dam's production only partially achieved the latter objective. Since, on the average, the productive spans of dams and daughters overlap only partially, year to year trends in environmental levels are not wholly removed. The use of the daughter-dam pairs was not restricted to records made in the same herd, which presented even further complications. As the use of artificial insemination (AI) increased, the need for more accurate evaluation become apparent. Consequently, the concept of the contemporary herdmate comparison was brought forward and has increased in popularity. This procedure helps eliminate environmental difficulties· that have presented problems in other methods of evaluation. With such a procedure, first lactation records of daughters of a sire are compared to other first lactation records. Both groups are adjusted to a 305-day length and mature equivalent basis and are initiated within the same herd-year-season. Comparisons of second and later records are also made under the same procedure. When first lactation are compared with those of their herdmates, bias is kept to a minimum, since neither group has .been subjected to culling practices. In_ most cases they have also been contemporaries since calfhood and have received the same treatment as calves, yearlings and bred heifers. The production differences of these groups would be as free from environmental influences as it is possible to make them. This study was initiated to evaluate the advantages offered through artificial insemination, in Holstein-Friesian cattle located within the three-state area of North Dakota, South Dakota and Nebraska within the years of 1958-1~64 through the use of herdmate comparisons. The main objectives of this study were as follows: 1) to measure the genetic superiority of artificially sired cattle in comparison to their naturally sired herdmates in terms of milk yield and fat production per lactation.2) to obtain a ranking of sires used within this three-state area in terms of

Library of Congress Subject Headings

Artificial insemination

Description

Includes bibliographical references (pages 42-45)

Format

application/pdf

Number of Pages

74

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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