Factors affecting the accuracy and stability of sire proofs from progeny test herds

dc.contributor.authorMeinert, Todd Richarden
dc.contributor.committeechairPearson, Ronald E.en
dc.contributor.committeememberCassell, Bennet G.en
dc.contributor.committeememberHoeschele, Inaen
dc.contributor.committeememberHobenboken, William D.en
dc.contributor.committeememberVinson, William E.en
dc.contributor.departmentAnimal Sciences, Dairyen
dc.date.accessioned2014-03-14T21:20:40Zen
dc.date.adate2005-10-10en
dc.date.available2014-03-14T21:20:40Zen
dc.date.issued1991en
dc.date.rdate2005-10-10en
dc.date.sdate2005-10-10en
dc.description.abstractChange in Modified Contemporary Comparison proofs during first and second crop period was computed from up to eight proofs during both periods for AI and non-AI sampled Holstein bulls with repeatability of last evaluation≥.90. Effect of proof number within testing period on the bull's milk or fat evaluation was estimated with bull absorbed. AI and non-AI sampled bulls' proofs increased from initial first crop proof and then remained fairly constant during the remainder of first crop period. With inclusion of second crop daughters, proofs dropped significantly more for non-AI than AI sampled bulls. This drop increased for non-AI sampled bulls born after 1976, but was unchanged for AI sampled bulls. A measure of change was calculated using last second crop proof minus the second to last first crop proof. Expected standard deviation of change was calculated and used to stratify bulls into eight change classes. A larger proportion of non-AI sampled bulls have proofs that dropped than could be explained by chance alo e. Results indicated that non-AI sampled bulls were less stable than AI sampled bulls' proofs and that stability of non-AI sampled bulls has diminished over time. For one of the studs that had stability of their bulls' proofs examined, their young sire sampling program was investigated. Individual phenotypic and genetic records of first crop and non-first crop cows in 3449 herds participating in the AI stud's young sire sampling program from 1971 to 1987 were used to characterize the sampling program, to estimate genetic trend across and within the progeny test herds, and to compute within herd means and standard deviations of various traits (herd characteristics). Herd characteristics of progeny test herds were utilized in predicting within herd genetic trend d in predicting changes in proofs of bulls sampled by the stud. For bulls sampled by this stud, average herd characteristics and variability of herd characteristics across the contributing herds was calculated and used to predict the measure of proof change in the first study. Average herd-year characteristics and variability of herd-year characteristics explained 39% to 46% of the variation in milk. and fat proof changes. In general, variability of herd-year characteristics and average within herd-year standard deviation herd-year characteristic variables explained most of the changes in proofs. Genetic trend across the progeny test herds was large for milk (105 kg) and fat (3.1 kg) yield. Genetic trend computed from PTAs of sires of first crop cows increased 58 kg milk and 1.5 kg fat per year from 1971 to 1978 and 176 kg milk. and 5.5 kg fat per year from 1979-87. The genetic level of daughters of young sires born after 1983 was equivalent or exceeded the genetic level of cows from other sires in the herd. Results indicated that within herd genetic improvement will not be hurt and may actually be enhanced from participating in a young sire sampling program depending upon sire selection of cows not bred to young sires. Herd characteristics explained forty-five and fifty-one percent of the differences in within herd genetic trends for milk and fat yield, respectively. Average sire PTA of non-first crop daughters accounted for 80% and 67% of the explainable differences. Other herd characteristics indicated that herds with larger within herd standard deviation milk yields, larger number of young sires represented, younger cows, less average days open, and greater percentage of cows sired by AI sires made faster rates of genetic improvement.en
dc.description.degreePh. D.en
dc.format.extentx, 114 leavesen
dc.format.mediumBTDen
dc.format.mimetypeapplication/pdfen
dc.identifier.otheretd-10102005-131543en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-10102005-131543/en
dc.identifier.urihttp://hdl.handle.net/10919/39701en
dc.language.isoenen
dc.publisherVirginia Techen
dc.relation.haspartLD5655.V856_1991.M456.pdfen
dc.relation.isformatofOCLC# 24073012en
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subject.lccLD5655.V856 1991.M456en
dc.subject.lcshAnimal genetics -- Researchen
dc.subject.lcshBullsen
dc.titleFactors affecting the accuracy and stability of sire proofs from progeny test herdsen
dc.typeDissertationen
dc.type.dcmitypeTexten
thesis.degree.disciplineAnimal Sciences, Dairyen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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