title: Genetic parameters for lamb birth weight, survival and death risk traits.
abstract: This paper reports genetic parameters for lamb survival and mortality traits on sheep farms in New Zealand. Lamb survival and mortality records were obtained from 38 flocks (103,357 lambs) from 5 yr of lambing data (2007 to 2011) and include many breeds and their crosses (predominantly Romney, Perendale, Coopworth, and Texel). A number of models were tested, all including environmental weather effects and investigating the random environmental effect of dam and litter (dam/year) as well as logit transformation for binary traits. Total heritability (direct + maternal) estimates were low for lamb viability at birth (0.01), lamb death risk to dystocia (0.01), and lamb death risk to starvation exposure (0.01) from birth to 3 d of age in an analysis accounting for direct and maternal genetic effects and the maternal environmental effects. Lamb survival heritabilities reported are very low (total heritabilities range from 0.02 to 0.06). The total heritabilities for the lamb death risk traits are lower than reported estimates of survival to 3 d of age or to weaning suggesting selection for the postmortem traits are not warranted at this time within these flocks. The total heritability for lamb birth weight was moderate (0.38) and the genetic correlations with the lamb death risk traits suggested that directional selection on lamb birth weight would have an effect on survival, although it is likely to have a nonlinear effect and therefore an optimum birth weight at which survival is maximized. This study has also shown that the total heritabilities may be overestimated when not accounting for maternal genetic and environment effects and in particular not accounting for the random environmental effect of litter (dam/year).
authors.affiliation: AgResearch Limited, Invermay Agricultural Centre, AgResearch, Puddle Alley, Private Bag 50034, Mosgiel, New Zealand julie.everett-hincks@agresearch.co.nz.
authors.forename: J M
authors.initials: JM
authors.lastname: Everett-Hincks
authors.affiliation: AgResearch Limited, Invermay Agricultural Centre, AgResearch, Puddle Alley, Private Bag 50034, Mosgiel, New Zealand.
authors.forename: H C
authors.initials: HC
authors.lastname: Mathias-Davis
authors.affiliation: AgResearch Limited, Invermay Agricultural Centre, AgResearch, Puddle Alley, Private Bag 50034, Mosgiel, New Zealand.
authors.forename: G J
authors.initials: GJ
authors.lastname: Greer
authors.affiliation: AgResearch Limited, Invermay Agricultural Centre, AgResearch, Puddle Alley, Private Bag 50034, Mosgiel, New Zealand.
authors.forename: B A
authors.initials: BA
authors.lastname: Auvray
authors.affiliation: AgResearch Limited, Invermay Agricultural Centre, AgResearch, Puddle Alley, Private Bag 50034, Mosgiel, New Zealand.
authors.forename: K G
authors.initials: KG
authors.lastname: Dodds
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D000831:Animals, Newborn / Q000033:anatomy & histology; D001724:Birth Weight / Q000235:genetics*; D001947:Breeding / Q000379:methods; D005260:Female; D008297:Male; D009026:Mortality; D019655:Quantitative Trait, Heritable; D012307:Risk Factors; D012756:Sheep / Q000033:anatomy & histology / Q000235:genetics* / Q000502:physiology
keywords: birth weight; heritability; lamb death risks; lamb survival