PMID- 26549545
OWN - NLM
STAT- MEDLINE
DCOM- 20161213
LR  - 20181202
IS  - 1751-732X (Electronic)
IS  - 1751-7311 (Linking)
VI  - 10
IP  - 3
DP  - 2016 Mar
TI  - Comparison between linear and proportional hazard models for the analysis of age 
      at first lambing in the Ripollesa breed.
PG  - 365-71
LID - 10.1017/S1751731115002220 [doi]
AB  - Age at first lambing (AFL) plays a key role on the reproductive performance of 
      sheep flocks, although there are no genetic selection programs accounting for 
      this trait in the sheep industry. This could be due to the non-Gaussian 
      distribution pattern of AFL data, which must be properly accounted for by the 
      analytical model. In this manuscript, two different parameterizations were 
      implemented to analyze AFL in the Ripollesa sheep breed, that is, the 
      skew-Gaussian mixed linear model (sGML) and the piecewise Weibull proportional 
      hazards model (PWPH). Data were available from 10 235 ewes born between 1972 and 
      2013 in 14 purebred Ripollesa flocks located in the north-east region of Spain. 
      On average, ewes gave their first lambing short after their first year and a half 
      of life (590.9 days), and within-flock averages ranged between 523.4 days and 
      696.6 days. Model fit was compared using the deviance information criterion (DIC; 
      the smaller the DIC statistic, the better the model fit). Model sGML was clearly 
      penalized (DIC=200 059), whereas model PWPH provided smaller estimates and 
      reached the minimum DIC when one cut point was added to the initial Weibull model 
      (DIC=132 545). The pure Weibull baseline and parameterizations with two or more 
      cut points were discarded due to larger DIC estimates (>134 200). The only 
      systematic effect influencing AFL was the season of birth, where summer- and 
      fall-born ewes showed a remarkable shortening of their AFL, whereas neither birth 
      type nor birth weight had a relevant impact on this reproductive trait. On the 
      other hand, heritability on the original scale derived from model PWPH was high, 
      with a model estimate place at 0.114 and its highest posterior density region 
      ranging from 0.079 and 0.143. As conclusion, Gaussian-related mixed linear models 
      should be avoided when analyzing AFL, whereas model PWPH must be viewed as better 
      alternative with superior goodness of fit; moreover, the additive genetic 
      background underlying this reproductive trait supports its inclusion into current 
      genetic selection programs given its economic importance.
FAU - Casellas, J
AU  - Casellas J
AD  - Grup de Recerca en Millora Genetica Molecular Veterinaria,Departament de Ciencia 
      Animal i dels Aliments,Universitat Autonoma de Barcelona,08193 
      Bellaterra,Barcelona,Spain.
LA  - eng
PT  - Comparative Study
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
DEP - 20151109
PL  - England
TA  - Animal
JT  - Animal : an international journal of animal bioscience
JID - 101303270
SB  - IM
MH  - Age Factors
MH  - Aging/*physiology
MH  - Animals
MH  - Birth Weight
MH  - Breeding
MH  - Female
MH  - *Linear Models
MH  - Meat/economics
MH  - Parturition
MH  - Phenotype
MH  - Pregnancy
MH  - *Proportional Hazards Models
MH  - Reproduction/genetics/*physiology
MH  - Seasons
MH  - Selection, Genetic
MH  - Sheep, Domestic/classification/genetics/*physiology
MH  - Spain
OTO - NOTNLM
OT  - Gaussian linear model
OT  - age at first lambing
OT  - proportional hazard model
OT  - ripollesa breed
OT  - sheep
EDAT- 2015/11/10 06:00
MHDA- 2016/12/15 06:00
CRDT- 2015/11/10 06:00
PHST- 2015/11/10 06:00 [entrez]
PHST- 2015/11/10 06:00 [pubmed]
PHST- 2016/12/15 06:00 [medline]
AID - S1751731115002220 [pii]
AID - 10.1017/S1751731115002220 [doi]
PST - ppublish
SO  - Animal. 2016 Mar;10(3):365-71. doi: 10.1017/S1751731115002220. Epub 2015 Nov 9.