New Zealand Journal of Agricultural Research abstracts
Genetic and environmental factors affecting lamb survival at birth and through
to weaning
C. A. MORRIS
S. M. HICKEY
J. N. CLARKE
AgResearch
Ruakura Agricultural Research Centre
Private Bag 3123
Hamilton, New Zealand
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). Corresponding
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.
Keywords Romney; lamb; genetics; perinatal survival; birth
weight
New Zealand Journal of Agricultural Research, 2000, Vol. 43: 515-524
0028-8233/00/4304-0515 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (730K); (scanned from paper original: notes about this process)
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