view - Department of Reproduction, Obstetrics and Herd Health

CHAPTER 5.1
However, this is minor compared with the glycerol released during extensive
mobilisation of adipose tissue in early lactation (up to 433 g/d; Drackley et al., 2001).
Finally, de novo synthesis of SCFA requires 0.5 mol of BHBA per mole of FA (Dado et al.,
1993). Taking into account the milk FA profile of milk in the current trial (Table 3), ALG
depressed fat synthesis by 1.23 mol/d FA saving 0.3 mol BHBA (Dado et al., 1993),
which represents about 0.78 of the BHBA requirement for milk FA production in the
CON. The unused BHBA surplus might be at the origin of the 1.2 to 1.4 fold BHBA
concentration in blood serum (0.88/0.73 = 1.20, Table 3) and FF (0.99/0.72 = 1.38,
Table 4) of ALG versus CON cows. Further, a higher butyrate production in the rumen, as
suggested from rumen FA proportions of ALG fed cows (Boeckaert et al., 2008), also
could have contributed to higher BHBA in blood and FF as observed in the current trial.
Hence, the approach of taking both metabolic limitations and nutrient requirements in
early lactation into account seems to be more capable of explaining observations seen
during MFD in high yielding dairy cows.
CONCLUSIONS
Santos et al. (2008) stated that improved reproductive performance have not
consistently been observed when feeding FA to dairy cattle especially when
accompanied with an increased milk yield and a loss in body weight. The results from
the current study substantiate this statement as increased BHBA concentrations in the
FF that have been associated with poor reproductive performance in high yielding dairy
cows were detected in the PUFA supplemented group (ALG). However, when calculating
nutrient requirements during MFD in early lactation, increased BHBA concentrations
can be attributed to a nutrient saving effect at the udder level. In conclusion, the
downregulation of de novo milk fat synthesis has 2 main consequences. The first is an
increased milk production most likely caused by a propionate saving effect when milk
fat is depressed and the second, an increased BHBA concentration in the FF that cannot
be attributed to a worsened energy status of the animals as all other indicators
contradict any change in EBAL, indicating that BHBA might not be an appropriate
metabolic parameter to estimate the EBAL in early lactating dairy cows during MFD.
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