Dietary lipids and forages interactions on cow and goat milk fatty acid composition and sensory properties
Reprod. Nutr. Dev.
Dietary lipids and forages interactions on cow and goat milk fatty acid composition and sensory properties
s CHILLIARD 0
FERLAY 0
0 INRA Unité de Recherches sur les Herbivores, Équipe Tissu Adipeux et Lipides du Lait , Theix, 63122 St-Genès-Champanelle , France
- This review summarises the known effects of dietary factors on bovine and caprine milk fatty acid composition, as well as the regulation of cow and goat mammary lipid secretion. Special attention is given to fatty acids that could play a role for human health, such as saturated fatty acids, oleic acid, n-6- or n-3-C18 to C22 polyunsaturated fatty acids, trans isomers of C18:1 and C18:2, and isomers of conjugated linoleic acid (CLA). The main dietary factors taken into account are the nature of forages, including pasture, the forage:concentrate ratio and diet starch content, and the supplementation of dairy rations with crude or processed vegetable oils or oilseeds, and vitamin E. A particular emphasis is given to studies on interactions between these dietary factors, which show that there is a considerable plasticity of ruminant milk fatty acid composition. Despite the existence of several studies on the effects of dietary factors on the sensorial quality of milk and dairy products, there is a need to evaluate more deeply how the different feeding strategies could change the nutritional, sensorial and technological aspects of milk fat quality.
-
Review
1. INTRODUCTION
Dairy products provide 25 to 35% of the
overall saturated fat consumed by man,
which makes them the preferential target of
dieticians’ criticisms [
1
]. The deleterious
reputation of saturated fatty acids (FA)
should however be weighted with the fact
that stearic acid has no atherogenic effect.
The allegedly atherogenic effect of certain
trans mono-unsaturated fatty acids has not
been confirmed as regards the main isomer
present in milk, i.e. vaccenic (trans11-18:1).
The interest of increasing the n-3/n-6 ratio
of polyunsaturated fatty acids (PUFA) has
been confirmed. Lastly, the properties of
conjugated linoleic acid (CLA), whose main
isomer, rumenic acid (cis9,trans11-18:2),
exhibits interesting features, as demonstrated in
animal models, are now better known, for
the prevention of certain forms of cancer in
particular.
These new facts underline the interest of
modulating the milk FA composition.
Mammals’ milk FA composition is linked to
intrinsic (animal breed, genotype, lactation
and pregnancy stages) or extrinsic
(environmental) factors. In a given animal
species, the effects linked to breed or genotype
are significant but restricted [
2–6
] and they
can only be achieved in the mid-term or
through interaction with constraints
inherent in other criteria. The lactation stage
effect is marked and mainly linked to lipid
1 Number of lipid-supplemented groups (amount of lipids, g·d–1).
2 Effects expressed as “treated group-control group”, * P < 0.05.
3 From [
20
].
4 Review by A. Ferlay and Y. Chilliard, unpublished.
5 Whole, rolled or ground.
store mobilisation in early lactation [
7
], but
it only lasts a few weeks each year. In
contrast, seasonal effects are quantitatively very
important. Although certain effects of
temperature or photoperiod can be evidenced,
it is the variations of ruminant nutrition which
determine most of the seasonal variations of
milk FA composition. The effects of
cheesemaking technology on FA composition are
minimal in relation to those of feeding [
8
].
Nutrition therefore constitutes a natural
and economical way for farmers to sharply
and rapidly modulate milk FA composition,
in particular by adding lipid supplements to
the diet. The consequences of these
practices on dairy cows’ milk fat and protein
synthesis and contents are now well known:
a tendency to increase milk production (with
saturated lipids and soybean in particular),
slight but almost systematic decrease in
protein contents, limited variations of the fat
content except with rapeseed oil and
especially with fish oil, which induce sharp
decreases, and encapsulated lipids that strongly
increase it (Tab. I). In contrast, nearly all
types of lipid supplements induce a sharp
increase in goat milk fat content without
modifying milk yield or protein content [
7
].
After a reminder of the mammary
lipogenesis metabolic pathways, this article
successively analyses the impacts of dairy
cows’ and goats’ diets on the main fatty acid
classes: saturated and cis mono-unsaturated,
polyunsaturated and lastly CLA and trans
mono-unsaturated. Then the effects of
nutrition on the sensory characteristics of dairy
products will be briefly evoked, as they may
partly be due to post-milking lipolysis of
milk fat (short-chain fatty acid release) or
to polyunsaturated fatty acid oxidation.
2. METABOLIC PATHWAYS
NUTRIENT FLUXES INVOLVED
IN MILK FAT SYNTHESIS
2.1. Mammary lipogenesis
Milk fatty acids have a dual origin: they
are either taken up from plasma
lipoproteins (60% (...truncated)