Selective breeding for rearing ability as an aid to improving lamb survival

Haughey, K. G.

doi:10.1111/j.1751-0813.1983.tb02848.x

Cited by 33 publications

(14 citation statements)

References 7 publications

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“…The high preweaning mortality recorded is consistent with estimates of mortality from major sheep producing countries, for example 5 to 25 per cent in New Zealand (Hight and Jury 1970), 22 per cent in Australia (Haughey 1983) and 10 to 35 per cent in the USA (Rook and others 1990). As in most flocks, there were constant attempts to improve lamb survival with the success being limited by the continually changing health status of the flock.…”

Section: Discussionsupporting

confidence: 81%

Risk factors for perinatal and postnatal mortality in lambs

et al. 1996

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Factors associated with preweaning mortality in lambs were identified by developing risk profiles with logistic regressions for perinatal and postnatal mortality. Compared with heavy lambs, lambs of low birth weight had almost twice the risk of perinatal mortality (odds ratio [OR] = 1.9) and lambs of average weight had a slightly lower risk (OR = 0.7). Two of four lambing location categories affected perinatal mortality, with lambs born at unmonitored areas at greatest risk (OR = 2.7). Multiple births increased the risk of perinatal mortality (OR = 1.5), especially among Targhee lambs (OR = 4.0). Breed variations in perinatal mortality were significant in Suffolk lambs (OR = 1.9) and Booroola Rambouillet lambs (OR = 2.1). Lambs born weak had an increased risk of postnatal mortality while strong lambs had a decreased risk (OR = 3.7 and 0.6, respectively) if the dam had an adequate milk supply. Poor milk supply increased the risk of postnatal mortality for lambs of average vigour (OR = 3.3), but did not change the risk for weak or strong lambs. Male lambs castrated at 30 days of age were at less risk of postnatal mortality (OR = 0.3) than females. There were slight increases in the risk of postnatal mortality for intact males (OR = 1.3), low birth weight lambs (OR = 1.6), and lambs born in sheds (OR = 1.3). Suffolk lambs (OR = 1.8) and Targhee lambs (OR = 1.6) had a higher risk of postweaning mortality.

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Section: Discussionsupporting

confidence: 81%

Risk factors for perinatal and postnatal mortality in lambs

et al. 1996

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“…Based on parameter estimates cited in the literature as well as those of the present study, most analysts would agree that the scope for selection for increased lamb survival rate is limited, although some genetic variation appears to exist. Yet, it has to be conceded that successes with regard to genetic gains in lamb survival and/or ewe rearing ability were reported in the literature (Donnelly, 1982;Haughey, 1983;Knight et al, 1998;. This may also be applicable to the flock under consideration, provided that a workable selection strategy can be devised.…”

Section: Discussionmentioning

confidence: 99%

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

Cloete¹,

Greeff²,

Lewer³

2001

SA J. An. Sci.

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Abstract(Co)variance estimates for birth weight, pre-weaning lamb survival and weaning weight were obtained for Merino lambs derived from 16 bloodlines. Between bloodline variance ratios (± s.e.) amounted to 0.10 ± 0.04 for lamb birth weight, 0.053 ± 0.036 for lamb survival (logit scale) and 0.18 ± 0.07 for lamb weaning weight. Direct additive genetic variances for weaning weight -expressed as a ratio of the total phenotypic variance within bloodlines (h², direct heritability) -were estimated at 0.18 ± 0.02 for birth weight, 0.094 ± 0.020 (logit scale) for pre-weaning survival and 0.30 ± 0.02 for weaning weight. Corresponding maternal genetic variance ratios (m²) were estimated at 0.15 ± 0.02 for birth weight and 0.08 ± 0.02 for weaning weight. It was not significant in the case of lamb survival. Maternal permanent environmental variance ratios (c²) amounted to 0.08 ± 0.02 for birth weight, 0.044 ± 0.018 for lamb survival (logit scale) and 0.07 ± 0.02 for weaning weight. These results were discussed with reference to sheep production.

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“…Unfortunately, the maternal and direct effects on survival appeared to be negatively correlated, so that making net genetic progress is not easy. However, it needs to be pointed out that some phenotypic progress (using selection among dams) has been made within a small number of flocks in New Zealand (Knight et al 1988) and Australia (Haughey 1983). The results of Knight et al (1988) suggest that a larger ratio of BW:dam weight contributed to the extra survival in the selected strain.…”

Section: Random Effectsmentioning

confidence: 99%

Genetic and environmental factors affecting lamb survival at birth and through to weaning

Morris

Hickey

Clarke

2000

New Zealand Journal of Agricultural Research

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Pedigree and early performance records from lambs on three New Zealand research stations, involving 51 station-years of data (55 146 recorded lambs born), were analysed in order to study genetic and environmental factors affecting perinatal and preweaning survival. Mean birth weights at each site were very similar, being 4.26 kg at Woodlands, 4.22 kg at Tokanui, and 4.32 kg at Rotomahana Station. Total survival rates to weaning (preweaning survival) across sites averaged 79.0, 78.9, and 80.1%, respectively. Analyses of variance for perinatal survival and preweaning survival showed significant effects of contemporary group of lamb, age of dam, and birth rank-sex combinations, whilst linear and curvilinear effects of birth weight were also significant. Optimal birth weights were 4.36 kg and 4.77 kg for maximal perinatal survival and maximal preweaning survival, respectively. Heavy singles and twins were at higher risk of not surviving, but light singles and twins were also at risk. At birth, survival was consistently lowest from lambs out of 2-year-old dams, whilst preweaning survival was lower amongst lambs from 2-and 5-year-old dams, and higher in lambs from 3-and 4-year-old dams.Estimates of total heritability (direct + maternal + direct-maternal covariance) for perinatal survival as a transformed (logit) trait were 0.055 (Tokanui and Woodlands data), and 0.105 (Rotomahana data). A00029 Received 7 June 2000; accepted 31 August 2000Corresponding estimates for preweaning survival were 0.031 and 0.101, respectively. Maternal genetic variances for perinatal and preweaning survival as logit traits were 1.5-5 times the size of the lamb's additive genetic variance. Our analyses confirm previous low genetic parameter estimates for lamb survival.

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Selective breeding for rearing ability as an aid to improving lamb survival

Cited by 33 publications

References 7 publications

Risk factors for perinatal and postnatal mortality in lambs

Risk factors for perinatal and postnatal mortality in lambs

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

Genetic and environmental factors affecting lamb survival at birth and through to weaning

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