Evaluation of phenotypic and genetic trends in weaning weight in Angus and Hereford populations in Virginia

Total weaning weight records of 29,832 Angus and 15,765 Hereford calves born during 1953 through 1983 in Virginia were used to evaluate phenotypic and genetic trends for adjusted weaning weight (AWWT), weaning weight ratio (WWR) and deviation of AWWT from the mean AWWT of the contemporaries (DEVN). Two approaches, namely the regression techniques and maximum likelihood (ML) procedure were taken to estimate the above trends. The estimates of annual phenotypic trend for AWWT in the Angus and Hereford breeds were .96 and .82 kg/yr, respectively. The sire and dam genetic trends obtained from both approaches for the traits of interest were positive and significant; however, the estimates from the regression analyses were slightly higher than those- from the ML procedure. The estimates of one-half of the sire genetic trends obtained from ML procedure for WWR and DEVN were .40 ± .04 ratio units/yr and .72 ± .07 kg/yr in the Angus breed and the corresponding values for the Hereford breed were .25 ± .06 ratio units/yr and .45 ± .12 kg/yr. The estimates of one-half of the darn trends for the corresponding traits were .32 ± .02 ratio units/yr and .55 ± .04 kg/yr for Angus and .21 ± .03 ratio units/yr and .30 ± .07 kg/yr for Herefords. The application of adjustment factors (to eliminate the bias due to non-random mating and culling levels) to estimates of sire genetic trends in the regression analyses produced estimates more similar to the estimates obtained from the ML procedure. The average annual genetic trends over the study period from the ML procedure for AWWT were 1.27 kg/yr for Angus and .75 kg/yr for Herefords.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Animal Science (Animal Breeding and Genetics)

Department dc:contributor.department

Animal Science (Animal Breeding and Genetics)

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1985

Author dc:creator

• Nadarajah, Kanagasabai

Chair dc:contributor.committeechair

• Marlowe, T.J.

Committee members dc:contributor.committeemember

• Notter, David R.
• Pearson, R.E.
• Hinkelmann, Klaus
• Eller, Arthur L. Jr.
• Swiger, L. Andy

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/74717

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/74717