Milk-and-Dairy-Products-in-Human-Nutrition-FAO

Chapter 3 – Milk and dairy product composition 59
Reindeer milk was reported to contain trans-FA at 3 g/100 g total FA and LA
(C18:2 n-6) at 2 g/100 g total FA, while moose milk contained more LA (average
8 g/100 g total FA) (Medhammar et al., 2011).
3.2.3 Factors affecting milk composition
Milk composition is affected by various factors, including stage of lactation, breed
differences, number of calvings (parity), seasonal variations, age and health of animal,
feed and management effects including number of milkings per day and herd
size (Laben, 1963; Bansal et al., 2003; Walker, Dunshea and Doyle, 2004; Jenkins and
McGuire, 2006). This section focuses on the effects of feed and stage of lactation.
Animal feed and milk composition
The influence of animal feed on milk composition has been, and continues to be,
the focus of many studies. Milk can be modified to improve it nutrient value and
sensory quality by changing the animal’s diet (Palmquist, Beaulieu and Barbano,
1993; Mesfin and Getachew, 2007; Castagnetti et al., 2008; Slots et al., 2009; Vera,
Aguilar and Lira, 2009; Wiking et al., 2010). For a review on the effects of nutrition
and management on the production and composition of milk fat and protein, see
Walker, Dunshea and Doyle (2004).
Several studies have looked at methods to increase long-chain n-3 PUFA (such
as docosahexaenoic acid [DHA] and eicosapentaenoic acid [EPA]), CLA and C18:1
trans-11 (vaccenic acid), all of which have been proposed to have beneficial effects
on human health (see Cruz-Hernandez et al., 2007, and references therein for
information on the effects of C18:1 trans-11). C18:1 trans-11 is produced in rumen
bacteria from dietary PUFA, and is subsequently converted by ∆ 9 -desaturase into
CLA in the tissues of ruminants (Cruz-Hernandez et al., 2007). Enrichment of
milk and meat fats of ruminants with CLA and C18:1 trans-11 depends on forageto-concentrate
ratio, the type of forage, the starch source in the concentrate, the
plant oil (e.g. sunflower, safflower oil, linseed etc.) added and its PUFA content
and composition and inclusion of fish oil, fish meal or algae (see Cruz-Hernandez
et al., 2007, and references therein). Plant secondary metabolites such as essential
oils, phenolic compounds and saponins have been suggested as a potential means
to manipulate bacterial populations involved in ruminal biohydrogenation and
thereby modify the FA composition of ruminant-derived food products such as
milk (Benchaar and Chouinard, 2009).
Grass-fed cows produce milk with significantly higher CLA contents than cows
fed concentrate-based diets, with values as high as 3.3 g/100 g total FA (Jutzeler van
Wijlen and Colombani, 2010). Slots et al. (2009) reported that an extensive feeding
system that incorporated pasture increased the CLA and C18:1 trans-11 content
in cow milk. The milk fat of cows grazed in the Alps has also been reported to
be exceptionally high in CLA, ranging from 1.9–2.9 g/100 g total FA (Kraft et al.,
2003), although it has been suggested that this may be linked to grass feeding in
general rather than being the result of a specific alpine pasture effect (Leiber et al.,
2005). Milk from grass-fed cows (irrespective of whether grazed or barn-fed) contained
up to 96 percent more ALA and 134 percent more α-tocopherol (attributed
to the high amounts of α-tocopherol in the grass), when compared with milk from
cows fed a silage-concentrate diet (Leiber et al., 2005).