view - Department of Reproduction, Obstetrics and Herd Health

GENERAL DISCUSSION
Even though some of these findings might be of particular interest, when
interpreting metabolites in early lactation dairy cows, some caution should be taken:
As described for the statistical analyses done in Chapter 5.1 and 5.2, the
distribution of metabolic parameters such as NEFA and BHBA are often right
skewed (Cozzi et al., 2011). This necessitates data normalization before analysis
with parametric tests (Duffield et al., 2003), which unfortunately is rarely
described. Even the residual errors from non-normally distributed outcomes are
unlikely to be ‘normalized’ by regression on the predictor variables in linear
regression models which are often used to analyze the effect of e.g. feeding
strategies on the metabolism in dairy cattle (Dohoo et al., 2003).
Especially in dairy cows which have a highly variable metabolism in early
lactation (Grummer, 2008), special care should be taken to prevent mis- or overinterpretation
of experiments with low number of animals.
Furthermore, as stipulated by Friggens et al. (2010), cows have a genetically
driven fat mobilization, which occurs in an environment that is in no way
constraining. By excluding diseased animals in research trials, which does not
represent the actual situation in most dairy herds, it might be difficult to find
statistically significant differences in metabolic parameters as mobilization in
these cows is mainly driven by their genetics rather than by the environment.
Recently, von Soosten et al. (2012) showed a decreased body mass mobilization
in early lactating dairy cows suggesting a protective effect of trans-10, cis-12 CLA
supplementation against excessive mobilization of body reserves. The induction
of a MFD might in other words be more useful in cows suffering from excessive
(environmentally driven) body reserve mobilization as compared to the more
intensively studied animals which remain healthy and solely suffer genetically
driven mobilization. Can in other words a MFD be used as a cure for diseased
animals rather than prevention of excessive NEBAL
Further research is needed to document the variability in production response to
a MFD especially in combination with the energy status of the animals. In this, metaanalysis
and meta-regression might provide greater statistical power in quantifying
overall production or reproduction responses than individual experimental studies
(Lean et al., 2009). The metabolic approach to a MFD has provided a better
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