Page 15 - Marieke Poppe

1 General introduction

improve the general capacity to be healthy – to improve resilience (Phocas et al.,
2016; Friggens et al., 2017). The breeding goal should thus be broadened even
further with resilience traits. The following paragraphs will explain the concept of
resilience in more detail, what efforts have been made into studying genetic
improvement of resilience, and will then introduce new methods that could be
used to genetically improve resilience.

1.4 Description of resilience and related concepts
The concept of resilience was first introduced in the field of ecology. Holling
(1973) defined resilience as the ability of systems to absorb disturbances and
maintain the same relationships between the components of the system.
Resilience is still a hot topic in ecology, and many efforts are being made to predict
so-called ‘critical transitions’ or ‘tipping points’ of ecosystems, where systems
suddenly switch to a different state (Dakos et al., 2008, 2012; Scheffer et al., 2009).
Through the years, other scientific disciplines have adopted the term as well, such
as psychology (Masten, 2001; Rutter, 2007; Amstadter et al., 2016), disaster
management (Rose, 2007; Whitson and Ramirez-Marquez, 2009), and gerontology
(Gijzel et al., 2017, 2019). In livestock, the concept was introduced during the last
decade, and the definition adopted in this thesis is ‘the capacity of the animal to be
minimally affected by a disturbance or to quickly recover’ (Colditz and Hine, 2016;
Ge et al., 2016; Berghof et al., 2019b).
In addition to the definition of resilience adopted in this thesis, many other
definitions of resilience for livestock exist, some of which are broader and some
more specific. A broader definition was given by Adriaens et al. (2020), who defined
resilience in dairy cows as the probability to complete several lactations, by
avoiding early culling by coping well with farm management conditions. Avoiding
early culling is determined by the ability to be minimally affected by disturbances
or to quickly recover, and by other traits such as milk yield and fertility. Other
studies used the more specific definition of disease resilience, which only focuses
on resilience to pathogenic or parasitic disturbances (Albers et al., 1987; Bisset and
Morris, 1996). Animals can have good disease resilience and keep functioning well
when faced with pathogens due to a combination of disease resistance and
tolerance. Resistance is the ability to limit pathogen burden and tolerance is the
ability to limit disease severity (Albers et al., 1987; Råberg et al., 2007; Knap and
Doeschl-Wilson, 2020), for example through tissue damage control (Soares et al.,
2014).
Before the term resilience was introduced in animal science, another closely
related term was used: robustness. This term was adopted around the time that

13