Analysing Resilience Indicator Traits in Austrian Fleckvieh, Brown Swiss and Holstein‐Friesian Cattle

Recent studies suggest that variations in milk yield during lactation can serve as a metric for assessing individual resilience, with minimum fluctuations reflecting greater resilience in cows. With automatic milking systems, multiple records can be obtained from many cows on a daily basis. Given that animals are continually exposed to a range of stressors throughout their productive life, identifying resilience traits is crucial for preserving both their productive and reproductive capacities. We studied two resilience indicators: natural log-transformed variance (ln(σ²)) and lag-1 autocorrelation (r_lag) of the daily deviations in milk yield recorded from the automatic milking system, with average daily milk yield incorporated as an additional trait to assess the correlations between the resilience indicators and milk yield. The resilience indicators were derived from three fitted lactation curves: the Wilmink curve, the penalised quadratic spline and the penalised cubic spline. The data consisted of 18,549,535 daily milk records of 37,118 Fleckvieh, 7322 Holstein-Friesian and 2784 Brown Swiss cows in 1070 Austrian dairy herds. The data were collected for lactation periods of up to 350 days across multiple parities. Additionally, the resilience indicators were calculated based on days 11-50 of lactation, as the transition period and early lactation are crucial moments for the cows. Genetic analyses were conducted using univariate and bivariate analyses to estimate heritability (h²) and genetic correlations between the traits. Estimated breeding values of the indicator traits obtained from the genetic analysis were correlated with routinely estimated breeding values and official indexes of the cows, including dairy, health, functional and conformation traits. The resilience indicators were scaled to negatives (-ln(σ²) and -r_lag) to compute these correlations, so that positive values indicate better resilience. The h² ranged between 0.09 and 0.20 for ln(σ²) and between 0.04 and 0.06 for r_lag, with the highest estimates observed when the penalised cubic spline was used. Generally, the h² decreased when only the early lactation period was considered. Genetic correlations of the resilience indicators with existing traits were low to moderate, with stronger correlations observed with -ln(σ²) than in -r_lag, particularly when estimated with the dairy traits. The negative correlations with milk yield, ranging from -0.13 to -0.45 for -ln(σ²) and -0.03 to -0.23 for -r_lag suggest that selecting for the resilience traits may result in a reduction in milk yield. This study demonstrated that deviations derived from fluctuations in lactation curves are heritable. Among the two resilience indicators evaluated, -ln(σ²) emerged as the more suitable trait for selection, considering its h² and positive correlation to health and functional traits. These findings underscore the potential for incorporating resilience traits into breeding programs while emphasising the need to balance improving resilience with milk production, considering the probable risk of reduced milk production in cows.