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

Abstract

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.

Effects of sire breed on ewe dystocia, lamb survival and weaned lamb output in hill sheep systems

“…sex) for lambs that died at birth, which tended to bias the data. However, for the lambs that died at birth and had sex recorded the ratio of males to females was 1 : 2, which follows published literature (Dalton et al, 1980;Morris et al, 2000). This is probably mostly due to its effect on birth weight (Nash et al, 1996;Holst et al, 2002).…”

“…This is probably mostly due to its effect on birth weight (Nash et al, 1996;Holst et al, 2002). The effect of age of ewe on lamb mortality has been shown by many authors to be important; often reported to generally decline with age up to the fourth or fifth parities (Dalton et al, 1980;Morris et al, 2000;Sawalha et al, 2007). In this study, the opposite was found.…”

Analyses of lamb survival of Scottish Blackface sheep

“…Single born lambs had higher mortality rate at birth but lower hazard rate afterwards (from 1 to 14 days). Morris et al (2000) found generally similar effects, with a higher rate of mortality at birth for lambs born to 2-year-old dams and a lower preweaning survival for lambs born to 2-and 5-year-old dams. Therefore, to reduce Lamb survival in Scottish Blackface sheep early postnatal lamb mortality, particular attention should be paid to 2-and 6-year-old ewes and their lambs and to twinand triplet-born lambs.…”

“…Early lamb survival is a complex trait that is influenced by the ewe's maternal ability and the lamb's capability for survival, in addition to the management practices and environmental variables at the time of birth and during the rearing period (Morris et al, 2000;Southey et al, 2001). Most studies of lamb survival (e.g.…”

“…Most studies of lamb survival (e.g. Burfening, 1993;Olivier et al, 1998;Morris et al, 2000) have used cumulative binary data analyses where animals are classified as alive or dead at the end of a period. However, the use of actual survival times through survival analyses enables the discrimination between lambs dying early or late in the period.…”