Page 15 - Marieke Poppe
P. 15

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.,
                         Before  the  term  resilience  was  introduced  in  animal  science,  another  closely
                      related term was used: robustness. This term was adopted around the time that

   10   11   12   13   14   15   16   17   18   19   20