J. Anim Sci.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

J. Anim Sci. 1986. 62:927-936.
© 1986 American Society of Animal Science
This Article
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Nwakalor, L. N.
Right arrow Articles by Richardson, G. V.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Nwakalor, L. N.
Right arrow Articles by Richardson, G. V.

Selection in Hereford Cattle. I. Selection Intensity, Generation Interval and Indexes in Retrospect

L. N. Nwakalor1, J. S. Brinks2 and G. V. Richardson3

Colorado State University, Fort Collins 80523

Abstract

Selection intensity and generation interval were evaluated in a Hereford cattle herd made up of 14 inbred lines and 14 linecross groups corresponding to the lines of inbred sires at the Suan Juan Basin Research Center, Hesperus, Colorado. Selection indexes practiced were calculated in retrospect. Analyses of the records collected from 1946 through 1973 involved weaning weight (WW) and postweaning traits in males and females. Analyses by line were performed for the inbreds, while pooled analyses were done on the inbred and linecross populations. From records of 1,239 calves weaned, age of sire averaged 3.75 yr compared with 4.52 yr for age of dam, showing faster generation turnover for sires than for dams. Generation interval determined as actual age of midparent was 4.13 yr. Selection applied for WW, evaluated as annual selection differentials within inbred lines and then pooled over all lines, averaged .55 standard deviations ({sigma})/generation for sires. For females, selection was much less intense. Midparent selection differential amounted to .33{sigma}/ generation. For sires, pooled standardized selection differentials per generation over all lines during the postweaning gain period were .49{sigma}, .46{sigma}, .40{sigma}, -.20{sigma}, -.10{sigma} and .69{sigma}, respectively, for initial weight, final weight, feed consumed, feed efficiency (FE, unadjusted and adjusted) and average daily gain (ADG). Selection of females for postweaning traits was not intense. Selection index actually practiced in retrospect for sires was: IS = .4461 (WW) – .0092 (FE) + .6126 (ADG). The indexes for dams included WW, 12-mo weight (12W), 18-mo weight (18W), mature spring weight (SPW) and mature fall weight (FAW) and were: for inbred dams, ID = .1824 (WW) – .0284 (12W) + .0736 (18W) – .1097 (SPW) – .1097 (FAW); for linecross dams, ID = .2693 (WW) – .2960 (12W) + .0147 (18W) + .1185 (SPW) – .0354 (FAW). The corresponding index selection differentials were .818, .203 and .209. Sire index selection differentials represent about 79% of the total selection differentials.

Footnotes

1 Present address: Dept. of Anim. Sci., Univ. of Nigeria, Nsukka, Nigeria.

2 Professor, Dept. of Anim. Sci., Colorado State Univ.

3 Biometrician, ARS, USDA, Fort Collins, CO 80523.






HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 1986 by the American Society of Animal Science.