Revised models and genetic parameter estimates for production and reproduction traits in the Elsenburg Dormer sheep stud

Abstract

Genetic parameters for production and reproduction traits in the Elsenburg Dormer sheep stud were estimated using records of 11743 lambs born between 1943 and 2002. An animal model with direct and maternal additive, maternal permanent and temporary environmental effects was fitted for traits considered traits of the lamb (birth and weaning weight and survival). Fixed effects were sex, birth status, year and age of dam. Weaning weights were pre-adjusted to a 100-day equivalent. For reproduction traits (considered as traits of the ewe), which included number and weight of lambs born and weaned, repeatability models were fitted. The random part consisted of direct additive and ewe and sire permanent environmental effects. Direct and maternal heritability estimates were 0.13 and 0.23 for birth weight and 0.07 and 0.09 for weaning weight. Corresponding proportions of total phenotypic variance due to maternal permanent and temporary environment were 0.09 and 0.28 and 0.06 and 0.22 respectively. The genetic correlation between animal effects was -0.23 in the case of birth weight. The results showed that temporary environment (full sibs within a year) generally has a major effect on all pre-weaning traits. The direct heritability estimate of survival was 0.02 while the temporary maternal environmental variance as a proportion of phenotypic variance was 0.10. The estimates obtained for number and weight of lambs born and weaned were generally low, ranging from 0.03 for number of lambs born to 0.11 for total weight at birth. The permanent environmental effect of the ewe accounted for 6-7% of the total phenotypic variance. Genetic correlations of total weight of lamb weaned with the other reproduction traits were generally high (0.64 to 0.92) with low standard errors. The corresponding phenotypic, environmental and ewe permanent environmental correlations were all medium to high and estimated with a fair deal of accuracy according to low standard errors. The genetic relationship between weaning weight of the ewe and her lifetime reproduction (accumulated over four lambing chances) ranged between 0.40 and 0.67. Correlations between number of lambs weaned per ewe and weight of lamb weaned per ewe were particularly high (0.8 -0.9). It was concluded that the maternal environmental effect should be partitioned into two components (permanent and temporary) when data sets involving multiple births over many generations are considered.

Estimation of genetic parameters for reproductive traits in Mehraban sheep

“…Mokhtari et al (2010) reported that the direct heritability for this trait was 0.18 which was the same value as calculated in the present research. This estimate was in the range of 0.03-0.4 as reported by several authors (Rosati et al 2002;van Wyk et al 2003;Mohamadi et al 2012;Amou Posht-e-Masari et al 2013;Mohammadabadi and Sattayimokhtari 2013). The heritability of TLWW was higher than of the other traits, which may be due to genetic variation in this trait according to the increase in the weaning weight of lambs (Mokhtari et al 2010;Rashidi et al 2011).…”

“…Heritability estimate for this trait varied from 0.01 to 0.189 (Bromley et al 2001;Rosati et al 2002;van Wyk et al 2003;Vanimisetti et al 2007;Ceyhan et al 2008;Amou Posht-e-Masari et al 2013). Lower heritability for LSW, compared with the heritability estimate for LSB, suggested that the loss of lambs from birth to weaning is influenced mainly by environmental factors such as a particular disease and mortality of lambs.…”

Genetic parameter estimation of 16-month live weight and objectively measured wool traits in the Tygerhoek Merino flock

“…The advent of these software packages enabled researchers to partition the respective random effects for various livestock species and breeds (Meyer, 1992;1994;Olivier et al, 1994;Purvis, 1995;Swan et al, 1995;Snyman et al, 1995;Meyer, 1997). In addition, Van Wyk et al (2003) and Safari et al (2007b) partitioned the dam environmental variance into a temporary litter effect and a permanent environmental effect (the correspondence of records of the same dam across breeding seasons) to accurately reflect the contribution of the respective components. Furthermore, Asadi Fozi et al (2005) reported the importance of including maternal genetic effects for fleece traits in Merino breeding programmes.…”

<b>Estimates of genetic and phenotypic parameters for reproductive traits in Iranian native Kordi sheep

“…The estimated direct additive heritability for TWLB/EL in this study (0.08) is consistent with the value of heritability reported for this trait by Fogarty (1995). The range of direct additive heritability for TWLB/EL was reported 0.04 to 0.4 by Matika, Van Wyk, Erasmus, andBaker (2003) andvanWyk et al (2003). TWLB/EL is a combination of the number of lambs born and the weight of lambs in each birth of ewe and indicates the ewe's capacity to produce kg weight of lamb without considering the number of lambs .…”