Genetic analysis of resilience indicators based on milk yield records in different lactations and at different lactation stages

摘要

Resilience is the ability of cows to cope with disturbances,such as pathogens or heat waves. To breed forimproved resilience, it is important to know whetherresilience genetically changes throughout life. Therefore,the aim was to perform a genetic analysis on 2resilience indicators based on data from 3 periods of thefirst lactation (d 11–110, 111–210, and 211–340) andthe first 3 full lactations, and to estimate genetic correlationswith health traits. The resilience indicators werethe natural log-transformed variance (LnVar) and lag-1autocorrelation (r_(auto)) of daily deviations in milk yieldfrom an expected lactation curve. Low LnVar and r_(auto)indicate low variability in daily milk yield and quickrecovery, and were expected to indicate good resilience.Data of 200,084 first, 155,784 second, and 89,990 thirdlactations were used. Heritabilities were similar basedon different lactation periods (0.12–0.15 for LnVar,0.05–0.06 for r_(auto)). However, the heritabilities of theresilience indicators based on full first lactation werehigher than those based on lactation periods (0.20 forLnVar, 0.08 for r_(auto)), due to lower residual variances.Heritabilities decreased from 0.20 in full lactation 1 to0.19 in full lactation 3 for LnVar and from 0.08 to 0.06for r_(auto). For LnVar, as well as for r_(auto), the strongestgenetic correlation between lactation periods was betweenperiod 2 and 3 (0.97 for LnVar, 0.96 for r_(auto)) andthe weakest between period 1 and 3 (0.81 for LnVar,0.65 for r_(auto)). Similarly, for both traits the genetic correlationbetween full lactations was strongest betweenlactations 2 and 3 (0.99 for LnVar, 0.95 for r_(auto)) andweakest between lactations 1 and 3 (0.91 for LnVar,0.71 for r_(auto)). For LnVar, genetic correlations withresilience-related traits, such as udder health, ketosis,and longevity, adjusted for correlations with milk yield,were almost always favorable (−0.59 to 0.02). In mostcases these genetic correlations were stronger basedon full lactations than on lactation periods. Geneticcorrelations were similar across full lactations, but thecorrelation with udder health increased substantiallyfrom −0.31 in lactation 1 to −0.51 in lactation 3. Forr_(auto), genetic correlations with resilience-related traitswere always favorable in lactation period 1 and in mostfull lactations, but not in the other lactation periods.However, correlations were weak (−0.27 to 0.15).Therefore, as a resilience indicator for breeding, LnVaris preferred over r_(auto). A multitrait index based on estimatedbreeding values for LnVar in lactations 1, 2, and3 is recommended to improve resilience throughout thelifetime of a cow.