Browsing by Subject "Dairy cows"

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Breeding for resilient cows
(2025) Keßler, Franziska; Bennewitz, Jörn
Dairy cows are an indispensable part of modern livestock farming and make a significant contribution to human nutrition with producing a high-quality protein. At the same time, they are influenced by environmental factors and must maintain their performance, stay healthy, and remain fertile under given environmental conditions. In recent decades, we have faced an increasing number of new or suddenly emerging environmental stressors: extreme weather events, heatwaves, invasive species, and constantly changing requirements for housing conditions are just a few examples. This demands a high level of robustness and resilience from our dairy cows. While comprehensive research has been conducted on adaptation to changing environmental conditions, there is still a lack of knowledge about coping with short-term disturbances. Resilience is the ability of an individual to respond to these disturbances, recover from them, and return to its previous physiological equilibrium while maintaining the same level of performance. This study examines the concept of resilience in German dairy cattle breeds, analyzes genetic parameters, and discusses possibilities for future breeding strategies. The first chapter describes interactions between organisms and the environment, as well as statistical approaches to assessing the influence of environmental gradients on livestock. The concepts of resilience and robustness were distinguished, and methods for measuring and phenotyping resilience were explored. A promising approach is the analysis of variance and autocorrelation of daily milk yields during lactation. Under the assumption that resilient animals maintain a stable performance level along a natural lactation curve, low variance and an autocorrelation close to zero indicate high resilience. The genetic parameters of these resilience indicator traits were studied in the second chapter for the three most important German dairy breeds: German Holstein, German Fleckvieh, and German Brown Swiss. Within each breed and across breeds, low to moderate heritabilities were observed, along with desirable phenotypic and genetic correlations with performance traits. A comparison between breeds revealed only minimal differences, with no clear trend across all resilience indicator traits studied. Next, correlations between resilience indicator traits and functional as well as health traits were analyzed. While hardly any significant correlations were found for autocorrelation, the variance of daily milk yield correlated in a desirable direction with these traits. Resilient animals appear to be healthier and more long-lived. Chapter three also discusses the design of a selection index for resilience. This requires economic weighting factors, which cannot yet be determined. Therefore, optimizing the selection index resilience by maximizing breeding response in the selection index health was proposed. It was shown that breeding for resilience would lead to genetic progress in overall health. In the German Holstein breed, which was exclusively considered in this context, a selection index consisting of two different variance-based resilience indicator traits was recommended. The adaptation of the methodology to optimize a selection index to the German Fleckvieh and German Brown Swiss breeds was subsequently addressed in the general discussion and considered feasible. The fourth chapter analyzes the genetic architecture of resilience using genome-wide association studies within the three dairy breeds. The results indicated that the resilience indicator traits are polygenic traits. SNPs that significantly influence resilience are located near to QTLs known to affect performance, fertility, or health. Additionally, population structure was examined using linkage disequilibrium analysis. The final general discussion applied the methods from chapter three to the German Fleckvieh and German Brown Swiss breeds. Significant negative, undesirable correlations between autocorrelation and functional and health traits were found in German Fleckvieh. In contrast, variance-based resilience indicator traits correlated positively with most known traits, which is desirable. A selection index resilience was proposed for both breeds, consisting of two to three individual indicator traits, similar to the German Holstein breed. To better understand resilience, differences in breeding values were translated into milk loss per lactation, the number of disturbances an individual suffered from, and the impact on test-day results for milk ingredients. Finally, an outlook was provided on potential future research directions for resilience in livestock.