Great Lakes Dairy Sheep Symposium - the Department of Animal ...

CLA. Examination of physiological factors has established that milk fat content of cis-9, trans-
11 CLA has little or no relation to milk or milk fat yield, parity, stage of lactation or breed (Lock
and Bauman, 2004). This variation must therefore, in large part, be related to individual
differences in rumen output of vaccenic acid and to a lesser extent cis-9, trans-11 CLA, and to
the amount and activity of Δ 9 -desaturase. Undoubtedly, the variation in Δ 9 -desaturase among
individuals has a genetic basis, and there is currently interest in understanding the genetic
variation and heritability of this enzyme. Increasing the activity of Δ 9 -desaturase via selection
and/or nutritional manipulation offer further potential to enhance the level of cis-9, trans-11
CLA in milk through increasing endogenous synthesis (Figure 3). Increasing Δ 9 -desaturase
activity would not only impact on the level of cis-9, trans-11 CLA in milk fat, but would also
increase other unsaturated fatty acids that are products of this enzyme. Finally, the final
concentration of cis-9, trans-11 CLA in dairy products is, in large part, related to the cis-9, trans-
11 CLA concentration in the raw milk fat and the fat content of the final product. Any changes
in the cis-9, trans-11 CLA content related to processing or to storage of dairy products are
minimal when compared to the variations associated with diet formulations and differences
among individual animals.
We have used such feeding regimes and taken advantage of individual animal variation to
produce cis-9, trans-11 CLA-enriched butter for use in biomedical studies with animal models. In
a series of studies, we have shown that dietary consumption of cis-9, trans-11 CLA-enriched
butter is effective in reducing the progression and incidence of tumors in a rat-model of
mammary cancer. These results are among the first to demonstrate that a naturally produced
anticarcinogen, consumed as a component of a natural food, is effective in reducing cancer.
Furthermore, vaccenic acid present in milk fat is also anticarcinogenic via its conversion to cis-9,
trans-11 CLA by our own Δ 9 -desaturase enzyme system. Recently, we have shown that naturallyderived
cis-9, trans-11 CLA also has potent antiatherogenic properties. See the review by Bauman
et al. (2005a) for a detailed discussion of the biological effects of cis-9, trans-11 CLA and vaccenic
acid.
The increased interest in the effect of bioactive fatty acids in milk fat has led to a number of
recent studies reporting the effects of different diets on the fatty acid composition of sheep milk. An
example of typical sheep milk fatty acid profile is shown in Table 3 and is taken from our study
reported earlier when ewes received the unsupplemented (Control) diet. In general, the
unsupplemented ewes had a milk fat content and fatty acid profile similar to other studies with
lactating sheep (Rotunno et al., 1998; Sevi et al., 2002). The content of cis-9, trans-11 in ewes
fed the control diet was however, lower than that reported in a survey of ewes when grazing
grass (Nudda et al., 2005), but comparable to values when a dried complete diet was fed (Luna et
al., 2005). A recent review examined the effect of forage species and stage of growth on the cis-
9, trans-11 CLA content of sheep milk fat under Mediterranean conditions (Cabiddu et al.,
2005). As for dairy cows, feeding fresh lush pasture results in the highest cis-9, trans-11 CLA
content of milk fat. Similarly, seasonal changes in the cis-9, trans-11 CLA content of sheep milk
have been reported which were related to pasture quality and availability (Figure 6; Nudda et al.,
2005). Finally, it has also recently been reported that the fatty acid composition of dairy
products (ripened cheeses and ricotta) produced from CLA-enriched milk were dependent on the
fatty acid composition of the starting raw milk, with manufacturing, ripening and storage having
little or no effect on the cis-9, trans-11 CLA content of the final product (Addis et al., 2005;
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