Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science


From May 1981 through January 1984, data were collected on 555,562 Holstein cows in the DHI program. The objectives of this study were: (1) to determine the completeness of reporting of dystocia, (2) to determine the economic influence of dystocia by age of cow on 305-day mature equivalent (ME) milk and milk fat production, days open and days dry, and (3) to implement the ordered categorical analysis procedure and to determine whether this method ranks sires differently than the method currently used by the NAAB;Thirty-four percent of the cows had dystocia scores reported. Data prior to June 1982 were not used because of inconsistent reporting of dystocia data leaving a total of 141,655 lactations with dystocia information;Days opens in first parity were 14 days greater for births scored 5 versus 1. The differences were larger in later parities. There were 26 more days open in second parity and 19 more days open in third and greater parities for score 5 versus 1;Differences between cows with score 5 and cows with score 1 were 465 kg ME milk and 20.7 kg ME fat less in first lactation, 576 kg ME milk and 20.9 kg Me fat less in second lactation and 725 kg ME milk and 25.0 kg fat less in third and greater lactations, with cows producing more in lactations following an easy birth;Sires with 5 progeny and herd-year-seasons having more than 14 sires were used to have a data set useful to estimate variance components. A total of 223 HYS and 189 sires were used for the standardized threshold model without relationships. The heritability estimate of the underlying continuous trait was .148. When relationships among sires were added the number of sires increased to 225 and the h('2) estimate became .147. Herd-year-season variance accounts for 13% of the total variance;Compared to the current national calving ease sire evaluation program the proposed threshold model compensates for two violations of major assumptions: (1) additivity of effects, and (2) homogeneity of variances. It allows computation of the Expected Percent Difficult First Calvings (4 or 5). Rank correlations among sire solutions were 76% and 79% without relationships and with relationships, respectively. Both approaches tend to agree on the most difficult sires.



Digital Repository @ Iowa State University,

Copyright Owner

Mnaouar Djemali



Proquest ID


File Format


File Size

85 pages

Included in

Genetics Commons