Environmental and genetic aspects of survival and early liveweight in Western Australian Merino sheep

Cloete, S.W.P.; Greeff, J. C.; Lewer, RP

doi:10.4314/sajas.v31i2.3838

Cited by 27 publications

(21 citation statements)

References 26 publications

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“…The estimate obtained in the present study (0.02), although non significant (i.e. at a level of two times the corresponding standard error), accords well with literature values which vary between 0.00 and 0.09 (Olivier et al, 1998;Snyman et al, 1998;Cloete et al, 2001;Matika et al, 2003). Lamb survival is a complex trait influenced by the lamb's own ability to survive and by its dam's rearing ability (Burfening, 1993).…”

Section: Resultssupporting

confidence: 90%

“…Estimates of the present study of 0.13 for h², 0.22 for m² and 0.09 for c² pe generally accords well with the range of literature values cited above. Corresponding estimates for weaning weight were 0.07, 0.08 and 0.07 respectively, which are in accordance with those of Boujenane & Kansari (2002) and are within the range of other literature values (0.06 to 0.39) (Cloete et al, 2001;Matika et al, 2003).…”

Section: Resultssupporting

confidence: 89%

“…Estimates (literature and present study) indicated that the selection response for increased lamb survival rate will be limited, although some genetic variation appears to exist. According to Cloete et al (2001) successes with regard to genetic gains in lamb survival and/or ewe rearing ability were reported in the literature. Parameter estimates fitting most appropriate models for reproduction traits (ewe traits) are presented in Table 5.…”

Section: Resultsmentioning

confidence: 99%

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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: 90%

Section: Resultssupporting

confidence: 89%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

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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“…Van Wyk et al, 1993;Maria et al, 1993;Snyman et al, 1996;Okut et al, 1999;Cloete et al, 2001, Maniatis & Pollott, 2002 and goats (e.g. Van Niekerk et al, 1996).…”

Section: Resultsmentioning

confidence: 99%

Model comparisons and genetic and environmental parameter estimates of growth and the Kleiber ratio in Horro sheep

Abegaz¹,

Wyk²,

Olivier³

2007

SA J. An. Sci.

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Genetic and environmental parameters were estimated for pre-and post-weaning average daily gain (ADG1, ADG2) and Kleiber ratio (KR1, KR2) using the ASREML program. Twelve models, formed with inclusion or exclusion of the maternal genetic, permanent environmental and common (litter) environmental variance components and the covariance between the direct and maternal additive effect on the basic direct additive genetic model, were used. The same models were applied to birth weight (BWT), weaning weight (WWT) and bi-monthly weights to 12 months of age (WT2 to WT12), and weight at 18 months of age (WT18). Two-trait analyses were done among all traits. Maternal genetic and common environmental components were found to be important for ADG1, KR1 and weights up to six-months of age, while the common environmental component was found to be important for ADG2 and KR2. The maternal permanent environmental component was important for WT2 and WWT. Total heritability estimates for ADG1, ADG2, KR1 and KR2 were 0.13, 0.04, 0.13, and 0.01, respectively. Direct genetic correlations of ADG1 with BWT, WWT and WT6 were 0.01, 0.96 and 0.84 while with KR1 they were -0.40, 0.75 and 0.66, respectively. The relatively higher heritability in weight traits and the presence of positive and high correlations of weight traits with daily gain and Kleiber ratio tend to suggest that it would be more practical to select on the weight traits to improve gain and efficiency.

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“…During the last 20 yr, an effective selection program has been carried out (Valera et al, 2002) on Spanish Merino sheep with an improved growth capacity and is now greater than in other sheep populations oriented toward wool production or dual purpose (Cloete et al, 2001;Duguma et al, 2002).…”

Section: Discussionmentioning

confidence: 99%

Random regression model of growth during the first three months of age in Spanish Merino sheep1,2

Molina

Menéndez-Buxadera

Valera

et al. 2007

Journal of Animal Science

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A total of 88,727 individual BW records of Spanish Merino lambs, obtained from 30,214 animals between 2 and 92 d of age, were analyzed using a random regression model (RRM). These animals were progeny of 546 rams and 15,586 ewes raised in 30 flocks, between 1992 and 2002, with a total of 45,941 animals in the pedigree. The contemporary groups (animals of the same flock, year, and season, with 452 levels), the lambing number (11 levels), the combination sex of lambs with type of litter (4 levels), and a fixed regression coefficient of age on BW were included as fixed effects. A total of 7 RRM were compared, and the best fit was obtained for a model of order 3 for the direct and maternal genetic effects and for the individual permanent environmental effect. For the maternal permanent environmental effect the best model had an order 2. The

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Environmental and genetic aspects of survival and early liveweight in Western Australian Merino sheep

Cited by 27 publications

References 26 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

Model comparisons and genetic and environmental parameter estimates of growth and the Kleiber ratio in Horro sheep

Random regression model of growth during the first three months of age in Spanish Merino sheep1,2

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