Background Many phenotypes in animal breeding are derived from incomplete measures,especially if they are challenging or expensive to measure precisely.Examples include time-dependent traits such as reproductive statu...Background Many phenotypes in animal breeding are derived from incomplete measures,especially if they are challenging or expensive to measure precisely.Examples include time-dependent traits such as reproductive status,or lifespan.Incomplete measures for these traits result in phenotypes that are subject to left-,interval-and rightcensoring,where phenotypes are only known to fall below an upper bound,between a lower and upper bound,or above a lower bound respectively.Here we compare three methods for deriving phenotypes from incomplete data using age at first elevation(>1 ng/mL)in blood plasma progesterone(AGEP4),which generally coincides with onset of puberty,as an example trait.Methods We produced AGEP4 phenotypes from three blood samples collected at about 30-day intervals from approximately 5,000 Holstein–Friesian or Holstein–Friesian×Jersey cross-bred dairy heifers managed in 54 seasonal-calving,pasture-based herds in New Zealand.We used these actual data to simulate 7 different visit scenarios,increasing the extent of censoring by disregarding data from one or two of the three visits.Three methods for deriving phenotypes from these data were explored:1)ordinal categorical variables which were analysed using categorical threshold analysis;2)continuous variables,with a penalty of 31 d assigned to right-censored phenotypes;and 3)continuous variables,sampled from within a lower and upper bound using a data augmentation approach.Results Credibility intervals for heritability estimations overlapped across all methods and visit scenarios,but estimated heritabilities tended to be higher when left censoring was reduced.For sires with at least 5 daughters,the correlations between estimated breeding values(EBVs)from our three-visit scenario and each reduced data scenario varied by method,ranging from 0.65 to 0.95.The estimated breed effects also varied by method,but breed differences were smaller as phenotype censoring increased.Conclusion Our results indicate that using some methods,phenotypes derived from one observation per offspring for a time-dependent trait such as AGEP4 may provide comparable sire rankings to three observations per offspring.This has implications for the design of large-scale phenotyping initiatives where animal breeders aim to estimate variance parameters and estimated breeding values(EBVs)for phenotypes that are challenging to measure or prohibitively expensive.展开更多
Before a breeder invests selection pressure on a trait of interest, it needs to be established whether that trait is actually heritable. Some traits may not have been measured widely in pedigreed populations, for exam...Before a breeder invests selection pressure on a trait of interest, it needs to be established whether that trait is actually heritable. Some traits may not have been measured widely in pedigreed populations, for example, a disease or deformity may become more prevalent than previously, but is still relatively rare. One approach to detect inheritance would be to screen a commercial population to obtain a sample of "affecteds" (the test group) and to also obtain a random control group. These indi- viduals are then genotyped with a set of genetic markers and the relationships between individuals within each group estimated. If the relatedness is higher in the test group than in the control group, this provides initial evidence for the trait being heritable. A power simulation shows that this approach is feasible with moderate resources.展开更多
基金funded by New Zealand dairy farmers through Dairy NZ Inc. and by the New Zealand Ministry of Business,Innovation and Employment (DRCX1302)support was kindly received from LIC and CRV
文摘Background Many phenotypes in animal breeding are derived from incomplete measures,especially if they are challenging or expensive to measure precisely.Examples include time-dependent traits such as reproductive status,or lifespan.Incomplete measures for these traits result in phenotypes that are subject to left-,interval-and rightcensoring,where phenotypes are only known to fall below an upper bound,between a lower and upper bound,or above a lower bound respectively.Here we compare three methods for deriving phenotypes from incomplete data using age at first elevation(>1 ng/mL)in blood plasma progesterone(AGEP4),which generally coincides with onset of puberty,as an example trait.Methods We produced AGEP4 phenotypes from three blood samples collected at about 30-day intervals from approximately 5,000 Holstein–Friesian or Holstein–Friesian×Jersey cross-bred dairy heifers managed in 54 seasonal-calving,pasture-based herds in New Zealand.We used these actual data to simulate 7 different visit scenarios,increasing the extent of censoring by disregarding data from one or two of the three visits.Three methods for deriving phenotypes from these data were explored:1)ordinal categorical variables which were analysed using categorical threshold analysis;2)continuous variables,with a penalty of 31 d assigned to right-censored phenotypes;and 3)continuous variables,sampled from within a lower and upper bound using a data augmentation approach.Results Credibility intervals for heritability estimations overlapped across all methods and visit scenarios,but estimated heritabilities tended to be higher when left censoring was reduced.For sires with at least 5 daughters,the correlations between estimated breeding values(EBVs)from our three-visit scenario and each reduced data scenario varied by method,ranging from 0.65 to 0.95.The estimated breed effects also varied by method,but breed differences were smaller as phenotype censoring increased.Conclusion Our results indicate that using some methods,phenotypes derived from one observation per offspring for a time-dependent trait such as AGEP4 may provide comparable sire rankings to three observations per offspring.This has implications for the design of large-scale phenotyping initiatives where animal breeders aim to estimate variance parameters and estimated breeding values(EBVs)for phenotypes that are challenging to measure or prohibitively expensive.
文摘Before a breeder invests selection pressure on a trait of interest, it needs to be established whether that trait is actually heritable. Some traits may not have been measured widely in pedigreed populations, for example, a disease or deformity may become more prevalent than previously, but is still relatively rare. One approach to detect inheritance would be to screen a commercial population to obtain a sample of "affecteds" (the test group) and to also obtain a random control group. These indi- viduals are then genotyped with a set of genetic markers and the relationships between individuals within each group estimated. If the relatedness is higher in the test group than in the control group, this provides initial evidence for the trait being heritable. A power simulation shows that this approach is feasible with moderate resources.
