Page 7 - Marieke Poppe
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Abstract

                      Poppe,  M.  (2022).  Genetic  improvement  of  resilience  in  dairy  cattle  using
                      longitudinal data. PhD thesis, Wageningen University, the Netherlands

                      Resilience is the ability of cows to be minimally affected by, and to quickly recover
                      from environmental disturbances, such as pathogens, extreme weather, or changes
                      in feed quality. Resilience is important for welfare of cows and work pleasure of
                      farmers, especially given an expected increase of disturbances in the future. This
                      thesis focuses on developing indicators of resilience from longitudinal data, based
                      on  the  expectation  that  longitudinal  data  records  show  response  patterns  to
                      disturbances, informative about resilience. Resilience indicators based on response
                      patterns can potentially assist in selecting the genetically most resilient animals for
                      breeding, and in identifying resilience at herd level. The main focus of this thesis
                      was on the resilience indicators ‘variance’ and ‘autocorrelation’ of daily deviations
                      from expected values of milk yield and step count. Resilience is indicated by low
                      variance  (small  deviations  from  baseline)  and  low  lag-1  autocorrelation  (weak
                      dependency  between  subsequent  deviations  -  quick  recovery).  Variance  and
                      autocorrelation of daily deviations from expected milk yield were heritable (0.21
                      and  0.09,  respectively)  and  both  were  genetically  similar  within  and  between
                      lactations.  Variance  seems  informative  about  vulnerability  and  strength  of
                      response to disturbances, based on genetic correlations with milk loss upon real-
                      life  disturbances  and  with  health,  longevity  and  fertility.  Autocorrelation  had  a
                      favorable genetic correlation with recovery rate upon disturbances. Furthermore,
                      variance was associated with lifetime gross margin, which confirms its economic
                      importance. Levels of variance and autocorrelation differed considerably between
                      herds, suggesting herd management plays a role in resilience. When based on step
                      count instead of milk yield, variance and autocorrelation were heritable (0.14 and
                      0.04), and autocorrelation was favorably genetically correlated with health traits
                      and fertility. However, variance had unfavorable genetic correlations with health.
                      Additional  traits  based  on  step  count  were  also  heritable  (especially  mean  step
                      count;  0.45),  but  more  research  is  needed  into  their  relations  with  resilience.
                      Genetic selection on a resilience index based on variance and autocorrelation of
                      milk  yield  deviations,  and  potentially  autocorrelation  based  on  step  count
                      deviations, is expected to result in more resilient cows, that are less affected by
                      disturbances and that recover more quickly.






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