view - Department of Reproduction, Obstetrics and Herd Health

GENERAL DISCUSSION
The scope of the present thesis was to get a better insight (Chapter 4) in the
transition period which cows have to endure every time they have calved and (Chapter
5) in the challenges when implementing dietary fatty acids (FA) to improve metabolic
health and subsequent fertility in dairy cows. More specifically, in the first part of
Chapter 4 (Chapter 4.1) we focused on the effect of metabolic diseases (MD) on milk
production and the shape of the lactation curve. In the second part (Chapter 4.2), we
estimated the preferential site from which fat is mobilized during negative energy
balance (NEBAL), in cows suffering from a left displacement of the abomasum (LDA).
Furthermore, in the first part of Chapter 5, we examined the effect of a milk fat
depression (MFD) induced by feeding long chain FA on the degree of NEBAL (Chapter
5.1). In Chapter 5.2, the effect of supplementation with short and long chain FA on blood
(BL), follicular fluid (FF) and milk FA composition was investigated. In finalizing chapter
6, the association between fertility parameters and the level of unsaturated FA (UFA) in
bulk tank samples was examined in a large dataset. Here, we aimed to interpret the
latter observations using knowledge acquired in the former chapters in order to get an
answer to the question: “Unsaturated fatty acids in dairy cows: Do’s and Don’ts”
WHERE IT ALL STARTS : ‘TRANSITIONOLOGY’
During the lact decades, dairy cows have been intensively selected to produce more
milk, and as a result are nowadays generally called high yielding (Shook, 2006). The
increase in milk yield per cow has been reported worldwide (Belgium: Hostens and
Opsomer, 2012; Canada: Leblanc, 2010; the United States of America: Lucy, 2001 and
England: Royal et al., 2000).
“The current milk production world record is held by “Hartje Meyer Beacon 9792” who
produced 34,512 kg of milk in 365 days (32g/kg fat and 29g/kg protein).”
Although high yielding dairy cows convert feed (nutrients) more efficiently into
milk, and thereby provoking a smaller environmental impact when compared to lower
yielding cows (Capper et al., 2009; Garnsworthy, 2011), there are some important
downsides associated with the increased level of milk production and its accompanying
NEBAL which are described in Chapter 4.
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