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
robustness
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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