Comparison of estimates of repeatability and heritability for some production traits in Merino rams and ewes. I. Repeatability

Abstract

Repeatabilities of 10 traits, namely, greasy wool weight, clean scoured yield, clean wool weight, body weight, wrinkle score, face cover score, fibre population density, fibre diameter, staple length, and crimps per inch, were estimated in ewes and rams. Estimates ranged from 0.4 to 0.7 for the 10 traits in both sexes. In general, body weight was the most repeatable trait and face cover the least. There is no evidence of sex differences in repeatability of the traits studied. Correlations between pairs of records obtained at different ages were high in both rams and ewes. This finding, together with the high repeatability values for all the traits, suggests that selection of sheep based on a single record is probably sufficiently accurate for lifetime performance of these 10 traits in Merinos. The correlations between yearling records and subsequent records in ram were found to be in agreement with correlations between records taken at older ages. Early selection of rams for lifetime performance therefore is probably almost as efficient as selection at a later age, and it is suggested that this finding might also be found to apply to ewes.

Genetic parameters for breech cover, wrinkle and wool coverage scores and their implications for Merino sheep breeding programs and flock management

“…The high genetic correlations between the two age expressions of each trait, and between BDWR and NKWR, indicate that the same genes are controlling the expression of these traits at both the yearling and adult stage of assessment which is in agreement with earlier studies across a wide range of Merino genotypes and environments (Beattie, 1962;Jackson and James, 1970;Mortimer and Atkins, 1993;Lewer et al, 1995;Robinson et al, 2007;Mortimer et al, 2009;Scholtz et al, 2010). Previous research indicates that BDWR and NKWR are highly repeatable (Young et al, 1960;Beattie, 1961;Hatcher et al, 2009) across a range of superfine to broad wool Merino types which implies that a single measure of either trait would be sufficient to include in a breeding program for plainerbodied sheep.…”

Analysis of records of a Perendale flock V. Repeatabilities and genetic correlations between ages

“…The estimates of repeatability of NL W found in this study are not dissimilar to those reported by Young et al (1963), Purser (1965), Inskeep et al (1967), and Kennedy (1967) although the range of 0.12-0.25 published by Rae & Ch'ang (1955) is higher than that in Table 2.…”

“…It can be concluded from the accumulated evidence that FW is highly repeatable. Wright & Stevens (1953) and Young et al (1960) also observed that more widely spaced records are less repeatable than adjacent records.…”

“…This may be a reflection of breed or environmental differences but there were also differences in the methods of measuring fibre diameter. Young et al (1960), who produced the lowest estimates, used the cast method whereas Beattie (1961) used the projection microscope method. Mullaney et al (1970), who reported the highest of the Australian estimates, used the airflow technique which was also used in the present study.…”

“…The average repeatability was 0.62. The repeatability of FW has been computed by many researchers (e.g., Young et al 1960;Gjedrem 1969;Mullaney et al 1970;Eijke 1975). It can be concluded from the accumulated evidence that FW is highly repeatable.…”