Exploration of variance, autocorrelation, and skewness of deviations from lactation curves as resilience indicators for breeding

摘要

The ability of a cow to cope with environmental disturbances,such as pathogens or heat waves, is calledresilience. To improve resilience through breeding, weneed resilience indicators, which could be based on thefluctuation patterns in milk yield resulting from disturbances.The aim of this study was to explore 3 traitsthat describe fluctuations in milk yield as indicators forbreeding resilient cows: the variance, autocorrelation,and skewness of the deviations from individual lactationcurves. We used daily milk yield records of 198,754first-parity cows, recorded by automatic milking systems.First, we estimated a lactation curve for eachcow using 4 different methods: moving average, movingmedian, quantile regression, and Wilmink curve. Wethen calculated the log-transformed variance (LnVar),lag-1 autocorrelation (r_(auto)), and skewness (Skew) of thedaily deviations from these curves as resilience indicators.A genetic analysis of the resilience indicators wasperformed, and genetic correlations between resilienceindicators and health, longevity, fertility, metabolic,and production traits were estimated. The heritabilitiesdiffered between LnVar (0.20 to 0.24), r_(auto) (0.08to 0.10), and Skew (0.01 to 0.02), and the genetic correlationsamong the indicators were weak to moderate.For r_(auto) and Skew, genetic correlations with health,longevity, fertility, and metabolic traits were weakor the opposite of what we expected. Therefore, r_(auto)and Skew have limited value as resilience indicators.However, lower LnVar was genetically associated withbetter udder health (genetic correlations from −0.22 to−0.32), better longevity (−0.28 to −0.34), less ketosis(−0.27 to −0.33), better fertility (−0.06 to −0.17),higher BCS (−0.29 to −0.40), and greater dry matterintake (−0.53 to −0.66) at the same level of milk yield.These correlations support LnVar as an indicator ofresilience. Of all 4 curve-fitting methods, LnVar basedon quantile regression systematically had the strongestgenetic correlations with health, longevity, and fertilitytraits. Thus, quantile regression is considered the bestcurve-fitting method. In conclusion, LnVar based ondeviations from a quantile regression curve is a promisingresilience indicator that can be used to breed cowsthat are better at coping with disturbances.