Selection for Weaning Weight and Potweaning Gain in Hereford Cattle. I. Population Structure and Selection Applied

Abstract

Single trait selection was practiced in three lines of Hereford cattle derived from a common base population. Selection was practiced on males only within sire families for increased weaning weight (WW) in the WW line (WWL), for postweaning gain (PG) in the PG line (PGL) and at random in the control line (CTL). Females were culled on the basis of age or reproductive failure. Progeny of selected bulls were produced in two herds from 1970 through 1981. The data consisted of records on 2,467 progeny of 125 sires and 922 dams. Generations of selection to produce the 1981 calf crop were 1.96, 1.85 and 1.80 for WWL, PGL and CTL, respectively. For calves born in 1981, mean cumulative selection differentials (CSD) were 54.5 kg in WWL and 37.8 kg in PGL. Corresponding values in standard deviation units (SDU) were 2.31 and 1.68, respectively. Secondary selection differentials were 25 to 40% as large as selection differentials for the primary traits. Unintentional selection in the CTL in 1981 was 16.2 kg or .68 SDU for WW and .2 kg or .01 SDU for PG, respectively. Regressions of CSD on year were 4.1 kg or .17 SDU in WWL and 3.2 kg or .14 SDU in PGL. Realized selection differentials were approximately 88% of the potential selection differentials in both lines. Inbreeding coefficients of dam and calves in 1981 were 2.0 and 3.5% in WWL, 2.1 and 3.5% in PGL and 2.9 and 5.8% in CTL.

Realized heritability estimates in boars divergently selected for testosterone levels1,2

“…Cumulative selection differentials were calculated for each individual. Similar procedures were described by I rgang et al (1985). No corrections were made for inbreeding depression.…”

Estimates of covariance components and genetic parameters for growth traits in Tswana cattle selected for increased weaning or eighteen-month weights

“…Therefore, the importance of genetic parameters such as heritability, correlations and repeatability in traits of economic importance in beef cattle cannot be underrated. On the other hand, these parameters are population specific and hence can by no means be generalised (Irgang et al, 1985). As a consequence, many studies have been conducted in recent years across the world with the aim of estimating both phenotypic and genetic parameters and to evaluate their importance in designing breeding programmes for different beef cattle breeds in different production environments (Chevraux and Bailey, 1977;Davis, 1987;Mercadante et al, 2003;Koch et al, 2004;Yilmaz et al, 2004;Enns and Nicoll, 2008;Boligon et al, 2010;Cervantes et al, 2010;Boligon et al, 2013;Shumbusho et al, 2013).…”