Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Dairy Science


Accurate evaluation of dairy production records is essential if dairymen are to establish and maintain profitable dairy herds and efficient culling programs. Improper record evaluation may result in. saving breeding stock that otherwise might be eliminated. Many factors may influence the validity of individual production records. Adjustment factors, currently in use by the United States Department of Agriculture (USDA) for sire and cow evaluations, are generally accepted as removing the majority of these influences. Consequently, these factors are invaluable to practical dairymen. The adjustment factors, suggested by McDaniel, et al. (24) in 1967, take into account the geographical location, season of calving, breed, age at calving, and milking frequency for both milk and fat, independently of one another. These factors are regarded as being adequate in removing variation arising between herdmates. Reproductive efficiency is of economic importance to dairymen. The necessity for regular calving is vital in an efficient dairy operation in order to maintain longevity and maximize lifetime net returns. Calving interval and days open prior to conception are related measures of reproductive efficiency which may assist in production record evaluation. Days open prior to conception actually determine the carving interval, assuming a constant gestation length; consequently, examination of days open would appear more applicable in evaluation of reproductive influences on production. It must be realized that certain environmental factors, such as careful and skillful observation of animals, type of housing system, and nutritional practices, may enter into relationships between production and reproductive efficiency and therefore, these factors must be accounted for in the analysis of data. This study was undertaken to determine the relationships which exist between days open prior to conception and lactation production in South Dakota Holstein herds. The specific objectives of the study were as follows: 1. To determine the influence of days open on 305 day production. 2. To develop adjustment factors for days open, if warranted.3. To determine phenotypic correlations between days open and production.

Library of Congress Subject Headings

Dairy cattle


Includes bibliographical references (pages 33-36)



Number of Pages



South Dakota State University


In Copyright - Non-Commercial Use Permitted

Included in

Dairy Science Commons