Age trends in economically important traits of Merino ewes subjected to 10 years of divergent selection for multiple rearing ability

Cloete, S.W.P.; Gilmour, AR; Olivier, J.J.; Wyk, J.B. van

doi:10.4314/sajas.v33i1.3737

Cited by 15 publications

(12 citation statements)

References 23 publications

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“…It is, however, evident from Table 3 that pre-adjustments for sex and birth year of weaning weight resulted in the same models being chosen. A similar result was obtained by Cloete et al (2003a). According to log likelihoods for total birth weight the effect of service sire should be included in the model for corrected data.…”

Section: Resultssupporting

confidence: 70%

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

Wyk¹,

Fair²,

Cloete³

2004

SA J. An. Sci.

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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.

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Section: Resultssupporting

confidence: 70%

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

Wyk¹,

Fair²,

Cloete³

2004

SA J. An. Sci.

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“…Number of lambs weaned per ewe joined over three lambing opportunities (NLW3) was heritable at 0.12 ± 0.03 in the current study. Comparable estimates for NLW3 suggested a range of 0.02 to 0.29 (Fogarty et al, 1994;Snyman et al, 1998b;1998c;Olivier et al, 2001;Cloete et al, 2002;Duguma et al, 2002;Cloete et al, 2003;Van Wyk et al, 2003;Cloete et al, 2004;Safari et al, 2005;Olivier & Cloete, 2006;Vatankhah & Talebi, 2008;Afolayan et al, 2009;Mokhtari et al, 2010;Rashidi et al, 2011;Mohammadi et al, 2012;Boujenane et al, 2013;Olivier, 2014). The current estimate of NLW3 is higher than the value of 0.05 derived from eight reports by Safari et al (2005).…”

Section: Resultsmentioning

confidence: 99%

“…These animals were divergently selected initially for their ability to rear multiples since 1986 using maternal ranking values for lambs reared per joining, which was subsequently aided by single-trait repeatability model breeding values as described by Cloete et al (2003;2004;. The animals providing data were progeny born between 1986 and 2012.…”

Section: Methodsmentioning

confidence: 99%

“…(Cloete & Scholtz, 1998;Cloete, 2002). Other details of the locality, management practices and recording of data in this flock can be found in the literature (Cloete & Scholtz, 1998;Cloete et al, 2003;Cloete et al, 2004;Cloete et al, 2009). Traits included in the analyses were ewe reproduction traits, which included number of lambs born (NLB1), number of lambs weaned (NLW1), and total weight weaned (TWW1) per ewe at first parity at two years of age, number of lambs born (NLB3), number of lambs weaned (NLW3) and total weight of lamb weaned (TWW3) per ewe over a three-year period from their lambing opportunities at two years of age to four years of age; objectively measured wool traits included greasy fleece weight (GFW), clean fleece weight (CFW), clean yield (CY), fibre diameter (FD), staple length (SL), and staple strength (SS).…”

Section: Methodsmentioning

confidence: 99%

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Genetic parameters for ewe reproduction with objectively measured wool traits in Elsenburg Merino flock

Matebesi-Ranthimo¹,

Cloete²,

Wyk³

et al. 2017

SA J. An. Sci.

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Reproduction is important for sustainable lamb production in Merino sheep. Data from a Merino flock maintained at Elsenburg Research Farm in the Western Cape, South Africa, were used to investigate the genetic parameters for ewe reproduction traits and their relationship with objectively measured wool traits. Traits included number of lambs born during the first lambing opportunity (NLB1), number of lambs weaned during the first lambing opportunity (NLW1), total weight of lamb weaned during the first lambing opportunity (TWW1), number of lambs born during a ewe's lifetime (NLB3), number of lambs weaned during a ewe's lifetime (NLW3), and total weight weaned per ewe's reproductive life (TWW3) Fixed effects of selection line, birth type, sex, age of the dam in years, year of birth, and the sex*birth year interaction had significant effects on all bodyweight and objectively measured wool traits. Only year of birth and selection line affected ewe reproduction traits. Heritability estimates amounted to 0.10 ± 0.03 for NLB1, 0.07 ± 0.02 for NLW1, 0.10 ± 0.04 for TWW1, 0.25 ± 0.04 for NLB3, 0.12 ± 0.03 for NLW3, and 0.18 ± 0.04 for TWW3. Wool traits were moderately heritable at 0.28 ± 0.05 (staple strength) to 0.60 ± 0.03 (clean yield (CY)) and coefficient of variation of fibre diameter (CVFD). Relationships among ewe reproduction traits were high, ranging from 0.74 between TWW1 and NLB3 to 1.00 between NLW1 and TWW1. The genetic relationships of ewe reproduction traits with wool weights and staple length were positive. Fibre diameter (FD) and CY were unfavourably related to ewe reproduction traits. It seems possible to improve ewe reproduction when selecting on NLB, NLW, and TWW in Merino sheep without unwanted correlated response to selection in wool traits, with the exception of FD and CY.______________________________________________________________________________

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“…Marked differences in reproduction rates have been reported for South African Merino lines divergently selected for multiple rearing ability 2,3 . On reproductive Columbia and Polypay ewes the density of lice were found to be higher than on unmated controls, although significance could not be established 13 .…”

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confidence: 99%

Infestation with the sheep body louse (Bovicola ovis) in Merino lines divergently selected for maternal multiple rearing ability : short communication

Cloete¹,

Laubscher²,

Cloete³

2003

J. S. Afr. Vet. Assoc.

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Data were obtained from a population consisting of 160 Merino ewes, as well as 64 male and 75 female progeny of these ewes at the 2-tooth age. The age and sex groups were maintained in separate flocks. The population has been divergently selected from the same base since 1986, either for (high or H line) or against (low or L line) maternal multiple rearing ability. All animals were inspected for sheep lice (Bovicola ovis) during September / October 2002 after a wool growth period of at least 4 months. When expressed relative to mean L-line performance, the advantage in lambs weaned per ewe during the lambing season amounted to approximately 110 % in the H line (1.01 vs 0.48; P < 0.01). The proportion of animals on which 1 or more lice were observed were markedly lower in 2-tooth replacement ewes than in replacement rams and mature breeding ewes (0.053 vs 0.625 and 0.531, respectively; P < 0.01). One or more lice were observed on a lower proportion of H-line ewes than on those of the L line (0.413 vs 0.571, respectively; P < 0.10), while a similar tendency was observed in 2-tooth ewe hoggets (0.033 vs 0.143, respectively; P =0.16). When the mean number of lice on individuals on which 1 or more lice were observed was compared between lines, the average number of lice observed on H-line young rams was lower than in the L line (4.36 Â± 0.85 vs 9.71 Â± 1.84 lice, respectively; P < 0.01). A similar tendency was observed in mature breeding ewes (2.15 Â± 0.38 vs 3.22 Â± 0.42 lice, respectively; P < 0.20). The more highly reproductive H-line ewes were not more susceptible to infestation with B. ovis than ewes of the L line. In fact, available evidence suggest that H-line animals could be more tolerant of B. ovis than those of the L line.

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Age trends in economically important traits of Merino ewes subjected to 10 years of divergent selection for multiple rearing ability

Cited by 15 publications

References 23 publications

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

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

Genetic parameters for ewe reproduction with objectively measured wool traits in Elsenburg Merino flock

Infestation with the sheep body louse (Bovicola ovis) in Merino lines divergently selected for maternal multiple rearing ability : short communication

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