Page 16 - Marieke Poppe
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1 General introduction

                the negative effects of selection on milk yield were recognized (Klopčič et al., 2009;
                Veerkamp et al., 2013). Like resilience, robustness has many definitions and some
                of  them  are  more  closely  related  with  resilience  than  others.  A  definition  of
                robustness closely linked to the definition of resilience of Adriaens et al. (2020), is
                the ability to carry on doing the various things an animal needs to do in the face of
                environmental constraints, to favor its future ability to reproduce (Friggens et al.,
                2017). Other studies state that robustness is different from resilience in the sense
                that robustness covers the ability of animals to function and maintain homeostasis
                in a broad range of environments, while resilience covers the ability to function in
                the face of short-term changes in one environment (Knap, 2005; ten Napel et al.,
                2009;  Colditz  and  Hine,  2016).  Although  concepts  such  as  disease  resilience  and
                robustness are not the same as the definition of resilience adopted in this thesis,
                they all encompass the desire for ‘trouble-free animals’. Therefore, the terms can
                often be used interchangeably.

                1.5 Previous efforts into genetic selection for resilience or
                   In the past 15 years, many studies addressed the need to breed for improved
                robustness, which is in many ways similar to improvement of resilience. The need
                for improved robustness was sparked by the unfavorable genetic trends for health
                and fertility mentioned earlier (Klopčič et al., 2009; Veerkamp et al., 2013). A book
                was published to summarize the state of the art knowledge on robustness in dairy
                cattle (Klopčič et al., 2009), and the RobustMilk project was started (Veerkamp et
                al., 2013). Robustness was a hot topic in pigs as well (Knap, 2005). In these studies,
                a number of methods to genetically improve robustness were proposed, that can
                be expected to improve resilience too.
                   The first method was to broaden breeding goals by adding additional health and
                fitness traits (Knap, 2005; Veerkamp et al., 2013). This method requires recording
                of  new  phenotypes  on  a  large  scale,  for  example  through  mid-infrared
                spectroscopy  of  milk  (Veerkamp  et  al.,  2013).  Since  the  desire  for  improved
                robustness  was  expressed,  indeed  new  traits  have  been  included  in  genetic
                evaluation in certain countries, such as ketosis resistance (Vosman et al., 2015) and
                hoof health (Egger-Danner and Heringstad, 2020) in dairy cattle.
                   The second method to improve robustness, specifically for dairy cattle, was to
                decrease negative energy balance in the first period of lactation (Veerkamp et al.,
                2013).  So  far,  specific  selection  against  negative  energy  balance  has  not  been
                performed. However, for example persistency of the lactation curve is genetically
                evaluated in the Netherlands (CRV, 2020g) and better persistency may be related

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