view - Department of Reproduction, Obstetrics and Herd Health

THE FABULOUS DESTINY OF FATTY ACIDS
example to ameliorate dairy cow fertility (Santos et al., 2008; Silvestre et al., 2011;
Thatcher et al., 2011).
CHALLENGES WHEN FEEDING FATTY ACIDS TO DAIRY CATTLE
BIOHYDROGENATION, ABSORPTION AND DISTRIBUTION OF FATTY ACIDS
The dietary FA reflect the FA composition of pig and poultry products in a
predictable way because they are absorbed unchanged before incorporation into the
tissue lipids (Chesworth et al., 1998; Woods and Fearon, 2009). In contrast, increasing
the amount of dietary UFA in the diet of ruminants is not linearly reflected in the body
tissues as microorganisms in the rumen largely affect the composition of the FA (Doreau
and Chilliard, 1997; Jenkins et al., 2008). The microorganisms are responsible for the
isomerisation and hydrolysis of dietary lipids, and the conversion of UFA to various
partially hydrogenated intermediates such as cis-9, trans-11 CLA or 18:1 trans-11, and
other fully saturated derivates such as 18:0 (Woods and Fearon, 2009). This process,
also called ruminal biohydrogenation (Figure 3), causes the major FA exiting the rumen
to be 18:0, although the main FA in most seed lipids and forages are 18:2n-6 and 18:3n-
3 respectively (Palmquist and Jenkins, 1980). In general, rates of rumen
biohydrogenation are faster with increasing unsaturation, showing hydrogenation rates
of 18:2n-6 and 18:3n-3 up to 70-95% and 85-100% respectively (Lock et al., 2006).
Biohydrogenation of 20:5n-3 and 22:6n-6 is still not well understood, but at present
they are believed to be hydrogenated at the same extent as 18:2n-6 and 18:3n-3
(Shingfield et al., 2010). Due to the extensive biohydrogenation of FA, ruminants seem to
have developed very efficient pathways for capturing and maintaining essential FA
within the body as functional deficiencies do not occur (Drackley, 2005).
There is no significant absorption or hydrogenation of LCFA in the omasum or
abomasums; the lipid material available for absorption in the small intestine is similar to
that leaving the rumen (Moore and Christie, 1984). Approximately 80-90% of lipids are
entering the small intestine as free FA attached to feed particles, bacteria and
25