milk of goats and cows (Massart-Leen et al., 1981). Monomethyl BCFAs with chain length shorter than ten carbon atoms were identified, successively, only in goat’s milk (Ha and Lindsay, 1993). Another 31 BCFAs, present at very low concentrations, were also identified: 25 of them are monomethyl branched, two are dimethyl and four are diethyl branched (Alonsoet al., 1999).
Among the ethyl ones, 4-ethyloctanoate, together with 4-methyloctanoate, give characteristic goat-like or mutton-like flavours to dairy products. Even though 3-methylbutanoate, 4-methylpentanoate and 8-methylnonanoate have also been identified in goat’s milk, they are not typical because they can be found in cow’s milk as well.
fat supplements and rumen fermentation compared with what occurs in dairy cows (Pulinaet al., 2006).
Such variable responses are probably linked to the energy balance of the animal, which varies with lactation stage and influences lipogenesis enzymes as well. In fact, the activity of such enzymes is enhanced from the beginning to the end of lactation, when the dietary FAs are preferentially utilized for the storage of body fat rather than for the endomammary synthesis of milk fat (Chilliardet al., 1991). The production responses to different types of fat supplements in the diet are quite uniform, except for unprotected fish oil, which has a negative influence on daily milk fat yield (Kitessaet al., 2001).
Effects of lipid supplementation on milk fat composition
The composition of milk fat is markedly influenced by the type of supplemented fat. It is well known that the addition of adequate lipid sources to ruminant feeds can change the FA composition of milk, whose profile reflects that of the diet, modified by rumen biohydrogenation and microbial activity. A diet supple- mented with palm oil, rich in palmitic acid (16:0), causes a remarkable increase in such FA and the corresponding MUFA (16:1) and a decrease in medium-chain FAs (from 10:0 to 14:0) and in oleic acid (cis-9 18:1). By contrast, diets rich in stearic acid (18:0) enhance the concentration of such FA
y = – 0.0001x2 + 0.0787x – 0.0944 R2 = 0.82
0 2 4 6 8 10 12
0 50 100 150 200 250
Increase in fat intake (g/day)
Increase in milk fat secretion (g/kg)
Fig. 3.6. Relationship between supplemented fat and milk fat secretion. Data represent means of dietary treatments and are referred to the whole lactation.
(Data sources for dietary treatments: Lu, 1993; Tehet al., 1994; Hadjipanayiotou, 1999; Brown-Crowderet al., 2001; Kitessa et al., 2001; Chilliard et al., 2002a, 2003; Rapettiet al., 2002; Sanz-Sampelayo et al., 2002; Bernard et al., 2005; Mele et al., 2005; Schmidely et al., 2005; Nudda et al., 2006; Andrade and Schmidely, 2006b.)
and of oleic acid, by the action of ∆9-desaturase in the mammary gland and decrease the content of medium-chain FAs.
In general, when plant oils or oilseeds are fed to ruminants, the PUFAs con- tained in the supplement are quickly hydrolysed in the rumen from their glycer- ides (Chilliard et al., 2002b; Antongiovanni et al., 2003), unless they are rumen-protected, e.g. by encapsulation (McDonald and Scott, 1977). The lower the protection, the higher is the increase in the levels of 18:0 and 18:1, at the expense of short- and medium-chain FAs (Sanz-Sampelayoet al., 2007). Some effects of protected and unprotected lipid sources in the diet (such as oil or raw or heat-treated oilseeds) on the FA composition of goat’s milk are illustrated in Tables 3.3 and 3.4. It can be seen that supplementation with protected oils increases 18:1, 18:2 and 18:3 in milk fat, depending on the content of these FAs in the lipid source. In the absence of protection, 18:0 and 18:1 are particularly enhanced, due to rumen biohydrogenation of PUFAs (Gulatiet al., 1997; Mir et al., 1999). With protected soybean oil, the increase in LA is also accompanied by an increase in 18:1 and 18:0, probably due to an incomplete protection of the oil. An efficient protection of plant oils supplemented to the diet enhances the absorption of PUFAs by the mammary gland from plasma.
As reported earlier in this chapter, PUFAs strongly limit theex novosynthe- sis of short- and medium-chain FAs. Therefore, the modification of the milk FA profile is related not only to an increase in PUFAs and LCFAs, but also to a decrease in the saturated and short- and medium-chain FAs. The supplemen- tation with protected cottonseeds increases the 18:2n–6 content and the 18:0 to 18:1 ratio in milk fat, although this supplement is poor in stearic acid and contains about 16% of 18:1. This fact may be due to the presence of cyclo- propenoid acids in cottonseeds, which are strong inhibitors of the endomammary
∆9-desaturase enzyme which catalyses the desaturation reaction of stearic acid to oleic acid.
y = 0.0481x + 0.1894 R2 = 0.97 0
2 4 6 8 10 12
0 50 100 150 200 250
Increase in fat intake (g/day)
Increase in milk fat secretion (g/kg)
Fig. 3.7. Relationship between supplemented fat and milk fat secretion. Data represent means of dietary treatments and are referred to early lactation. (Data sources for dietary treatments: Lu, 1993; Tehet al., 1994; Brown-Crowder et al., 2001; Meleet al., 2005; Nudda et al., 2006; Andrade and Schmidely, 2006b.)
Usually, PUFAs, CLA and VA of milk fat are increased more by feeding unprotected plant oils than by feeding seeds of oil plants, whereas extruded or heat-treated seeds cause an intermediate effect (Martinet al., 2004; Nuddaet al., 2006). When whole seeds are used, their oil becomes available in the rumen more gradually than when the unprotected oil is directly supplied. This leads to a more efficient reduction of PUFAs. Therefore, in this case, a higher amount of 18:0, which is the terminal product of the rumen biohydrogenation of PUFAs, is accumulated in the rumen. Even though such results were initially reported for dairy cows only, they have recently been confirmed for lactating goats supple- mented with oil plant seeds, e.g. linseeds or sunflower seeds, or with their unpro- tected oils (Chilliard et al., 2003). Milk fat content was increased (from 3 to 6 g/kg) by all treatments, while milk content of LA, LNA, VA and RA was mark- edly increased when goats were fed free oils rather than whole seeds. When lupin was added to the diet, the transfer of PUFAs to milk was less efficient com- pared with other whole seeds such as soybean or linseed. This could be due to the presence of a compound in lupin which results in a high degree of biohydro- genation (Chilliardet al., 2003).
Forage source and lipid supplementation
The effects of vegetable oil supplemented to the diet may also depend on the forage base of the diet. For example, adding sunflower oil with high oleic acid content to a grass hay-based diet leads to an FA profile of milk different from that
Saturated fatty acidsa Soybean oil Linseed oil Fatty acid 16:0 18:0 Protecteda Unprotectedb Protectedc Unprotectedd
4:0–8:0 +1.5 +0.5 +1.4 −0.91 −0.3 −0.5
10:0–14:0 −4.4 −4.2 +1.9 −4.83 −7.4 −8.6
16:0 +6.4 −6.2 −8.7 −4.15 −7.7 −8.9
16:1 +2.4 −2.0 ND −0.1 −0.3 ND
18:0 0.0 +7.0 +1.1 +1.5 +6.6 +4.8
18:1e −2.0 +6.6 +2.5 +10.5 +7.6 +5.5
18:2 −0.5 −0.6 +4.4 +0.5 −0.1 0
18:3 +0.3 −0.6 ND −0.1 +1.33 +1.27
cis-9, trans-11 CLA
ND ND ND +3.2 +0.3 +0.82
CLA, conjugated linoleic acid; ND, not determined.
aAdapted from Chilliardet al. (2003).
bAdapted from Meleet al. (unpublished data).
cAdapted from Bernardet al. (2005).
dAdapted from Chilliard and Ferlay (2004).
eSum ofcisandtransisomers.
Table 3.3. Effects of different lipid supplements supplied as oil on the fatty acid composition of milk (g/100 g lipids). Effects are expressed as the differences between fat-supplemented and non-supplemented control groups.
obtained with the same supplement added to a maize silage-based diet. In the first case, oleic acid and RA in milk fat increase the most, whereas in the latter casetrans-10 18:1, stearic acid and butyric acids show the highest increase. Sim- ilarly, linseed oil in association with maize silage increases the synthesis of 4:0 andtrans-10 18:1, while when associated with lucerne hay it increases RA and VA in milk fat (Chilliard and Ferlay, 2004). In general, the use of linseed oil increases thetransforms of MUFAs and PUFAs with 18 carbon atoms. However, due to the interaction between this supplement and the forage base, the propor- tions between the different isomers change depending on the rumen metabolic pathways favoured by the different diets. Unlike the situation in dairy cows, few data are available on the influence of feeding on the various CLA isomers in goat’s milk, whereas more information is available on goat’s milk content of transisomers of 18:1 (Alonsoet al., 1999; LeDouxet al., 2002). In general RA is the main CLA isomer in milk, because of its mammary synthesis by∆9-desaturase.
In addition, this enzyme also synthesizestrans-7,cis-9 CLA, which is quantitatively the second isomer present in milk. In general, high levels of RA in milk fat are accompanied by high levels of VA and of othertransisomers of 18:1 and conju- gated or non-conjugated 18:2 and 18:3 (Chilliard and Ferlay, 2004).
The interaction between the forage/concentrate ratio of the diet and the kind of supplemented fat may also affect milk FA composition in dairy goats.
Recently, Andrade and Schmidely (2006b) reported that feeding a high-concentrate diet combined with rolled canola seeds had a synergistic effect, which increased
Rapeseeda Cottonseedsa Extruded
linseed Rolled Extruded Fatty acid Protected Unprotected Protected Unprotected cakeb linseedc soybeand
4:0–8:0 ND ND ND −0.1 0 +0.3 ND
10:0–14:0 −0.6 −2.0 −2.1 −0.6 −2.0 −4.8 −5.8
16:0 −8.2 −4.1 −2.0 −4.3 −8.4 −10.2 −10.4
16:1 ND ND ND ND −0.2 −0.2 −0.1
18:0 −3.9 +5.8 +6.8 +6.6 +3.1 +5.0 +7.2
18:1e +7.9 +6.9 −11.3 +4.0 +5.9 +10.6 +5.3
18:2 +5.9 +1.1 +14.3 +0.2 0 −0.4 +1.7
18:3 +3.1 +0.5 0.0 +0.2 +0.5 +0.3 0
Cis-9,trans- 11 CLA
ND ND ND ND +0.5 +0.9 ND
CLA, conjugated linoleic acid; ND, not determined.
aAdapted from Chilliardet al. (2003).
bAdapted from Nuddaet al. (2006).
cAdapted from Andrade and Schmidely (2006b).
dAdapted from Schmidelyet al. (2005).
eSum ofcisandtransisomers.
Table 3.4. Effects of different lipid supplements supplied as oilseeds on the fatty acid composition of milk (g/100 g lipids). Effects are expressed as the differences between fat-supplemented and non-supplemented control groups.
the proportion of trans 18:1, LNA and RA in milk fat at the expense of medium-chain FAs. In addition, this combination increased milk production and milk fat yield, without changing milk protein content. Similarly, when dairy goats were fed high- or low-concentrate diets, with or without supplementation of unprotected soybean oil (4% on DM basis), Meleet al. (2005) found no detri- mental effect of soybean oil on milk fat yield and content. Moreover, soybean oil supplementation increased VA and RA milk content, regardless of the level of concentrate in the diet. These findings confirm that the influence of nutrition on milk fat content and secretion largely differs among ruminant species. In dairy cows, milk fat content is decreased by high-concentrate diets, especially if sup- plemented with unprotected PUFA-rich vegetable oils. By contrast, when dairy goats are fed vegetable oils, even added to low-fibre diets, milk fat content and yield almost always increase, and never decrease (Chilliard et al., 2005; Mele et al., 2005; Andrade and Schmidely, 2006b). According to the biohydro- genation theory of Bauman and Griinari (2001), MFD is caused by an increase oftrans-10 18:1 andtrans-10,cis-12 CLA, which sharply reduces mammary lipid secretion. In dairy goats, the lack of correlation between milk fat content and sev- eral CLA isomers, includingtrans-10,cis-12 CLA, could be related either to the fact that trans-10,cis-12 CLA did not increase above trace levels in milk, even whentrans-10 18:1 increased, or to the failure oftrans-10,cis-12 CLA to inhibit milk fat synthesis even when infused in the duodenum (Andrade and Schmidely, 2006a).
In order to increase n–3 FAs, such as eicosapentaenoic (EPA, 20:5) or docosahexaenoic (DHA, 22:5), in goat’s milk, fish oil is commonly supplemented in the diet. The introduction of such lipid sources in protected form in the diet of lactating goats, at 3% of DM intake, allows one to: (i) enrich the milk inn–3 FAs;
and (ii) avoid undesirable metabolic effects, such as reduced DM intake and pro- ductivity, and formation of transand hydroxyl FAs. In fact, the transfer rates of EPA and DHA were higher when fish oil was offered in the protected form (7.62 and 5.05% for EPA and DHA, respectively) than when offered without any pro- tection (2.50 and 3.53% for EPA and DHA, respectively) (Kitessaet al., 2001).
Green herbage in the ration is a source of fat substances capable of typically characterizing milk fat. For example, it is well known that green herbage increasescis-9,trans-11 CLA in ruminant milk, due to the large amount of LNA present in the green plant, compared with hay. This is because the oxidation processes following the cutting, drying and storage of hay significantly reduce its fraction of PUFAs. Nevertheless, the increment rate of CLA in grazing animals varies with ruminant species and pasture quality. Differences in milk CLA content have been observed among animals of different species fed the same pasture (Nudda et al., 2003) and among animals of the same species fed pastures with different botanical composition (Meleet al., 2007b).