Thesis - Open Access
Master of Science (MS)
One of the keys to financial success in the dairy business is the ability of management to detect herd problems and correct them instead of culling cows. It is well known that the average productive life of the dairy cow is less than 4 yr, which is short compared with her potential life. Involuntary removal of cows causes economic loss directly as a result of its effect on yearly milk production, increased replacement cost, and indirectly because the potential selection differential is reduced with premature loss of high producing cows. The degree of culling is related to important economic considerations such as the prices of milk and beef, as well as the prices of feed, and the cost and availability of labor. Studies on the disposal rates of cows from Dairy Herd Improvement Association (DHIA) and research herds have shown that a large portion of the cull cows were removed because of low production, reproductive problems, mastitis, sold for dairy purposes, and type related problems. Dairymen have indicated that low fertility is their number one herd problem despite the fact that there is no known infectious disease problem. Reproductive problems accounted for the largest amount of involuntary losses in studies of disposal rates of cows from DHIA and research herds. Reproductive failure in dairy cattle causes economic loss directly as a result of its adverse effect on yearly milk production and on surplus calves for sale, and indirectly because the potential selection differential is reduced with fewer replacements. Infertility in cows appears to be primarily a management problem. Heritability of breeding efficiency is low, thus, selection for breeding efficiency would not be effective and would be at the expense of other traits of economic importance which show a greater response to selection. Researchers have suggested that any effective evaluation of genetic differences for breeding efficiency among cows must await the development of new criteria. These tests should be simple and easily applied on a widespread basis. Most production variables considered in sire selection have medium to high repeatability and heritability estimates. Young sires are evaluated on first-lactation performance of this progeny, and any relationship with later performance of length of herd life would have an important bearing on the evaluations. Selection of highly productive cows without conscious emphasis on fertility will not lead to a population with markedly altered ability to reproduce. The reasons why cows were removed from the South Dakota State University dairy research herd were examined in this study. The results will serve as a guide for herdsmen and researchers to technical problems of management, breeding, and of disease on dairy farms. This study also examined the use of stepwise discriminant analysis to identify those cows with or without reproductive problems using the following selected discriminator variables: lactation number, yield of 305-ME milk, yield of 305-ME milk fat, age adjusted type score, difference from herdmates-milk, difference from herdmates-milk fat, percent protein-lactose-minerals (PLM), and yield of PLM. This analysis was also used to find a reduced set of discriminator variables.
Library of Congress Subject Headings
Dairy cattle -- South Dakota -- Reproduction
Includes bibliographical references (pages 55-59)
Number of Pages
South Dakota State University
Tidemann, Fred, "Reasons Why Cows Were Removed From the SDSU Fairy Herd 1. Discriminant Analysis to Classify Cows with or without Reproductive Problems" (1978). Theses and Dissertations. 1290.