Conjugated Linoleic Acids Alter Milk Fatty Acid Composition and Inhibit Milk Fat Secretion in Dairy Cows

Abstract

Conjugated linoleic acids (CLA) have positive health effects in experimental models. Our objective was to determine the effect of CLA supplementation on milk of dairy cows. A commercial source of CLA was infused abomasally to by-pass rumen fermentation. The supplement contained 61.2% CLA; the major CLA isomers were cis/trans 8,10, cis/trans 9,11, cis/trans 10,12 and cis/trans 11,13. Four Holstein cows were used in a 4 x 4 Latin square design. Treatments were 5-d infusions of 0, 50, 100 and 150 g/d of CLA supplement. Infusion increased milk fat content of CLA from 6.8 mg/g fat (zero dose) to 63.6 mg/g fat (highest dose). All of the major CLA isomers in the supplement were transferred to milk fat in a dose-dependent manner. Apparent efficiency of transfer to milk fat was 22.5, 22.5, 10.2 and 26.3% for cis/trans 8,10, cis/trans 9,11, cis/trans 10,12 and cis/trans 11,13, respectively. CLA infusion had no effect on milk protein and little effect on milk yield (21.5, 20.4, 20.9 and 18.3 kg/d for 0, 50, 100 and 150 g/d CLA supplement, respectively). However, CLA infusion dramatically reduced milk fat. On average, the content and yield of milk fat were reduced by 52 and 55%, respectively. The role of specific CLA isomers and mechanism(s) for the reduction in milk fat have not been established, although the pattern of milk fatty acids demonstrated effects were most pronounced on de novo fatty acid synthesis and the desaturation process. Overall, dietary supplemention of CLA increased milk fat content of CLA, altered milk fatty acid composition and markedly reduced the content and yield of milk fat.

Recent advances in the regulation of milk fat synthesis

“…Ip et al, 2002;Kelley et al, 2007) and reduced adiposity (reviewed by Pariza, 2004), although only a mixed preparation including both cis-9, trans-11 and trans-10, cis 12 CLA was available in the original experiments. Similarly, this mixed CLA preparation also reduced milk fat yield in dairy cows (Loor and Herbein, 1998;Chouinard et al, 1999a and1999b). Subsequently, the ability to prepare relatively pure CLA isomers allowed the seminal demonstration by Baumgard et al (2000) that trans-10, cis-12 CLA markedly reduced milk fat synthesis, whereas cis-9, trans-11 CLA had no effect ( Figure 2).…”

Genetic variability of milk fatty acids

“…The total concentrations of MUFAs and CLA should increase in fat if SCD activity rises, improving in this way the nutritional quality of milk. Some studies estimated SCD activity by specific FA indices, defined as ratios of FAs dependent on this enzymatic activity: product/substrate (e.g., Lock and Garnsworthy 2003), substrate/product (e.g., Chouinard et al 1999) or product/(substrate + product) (e.g., Kelsey et al 2003). Kelsey et al (2003) observed that Holstein cows showed higher FA indices compared to Brown-Swiss cows, except for CLA index.…”

Production performance and pattern of milk fat depression of high-yielding dairy cows supplemented with encapsulated conjugated linoleic acid

“…Biohydrogenation of polyunsaturated fatty acids (PUFAs) generates isomers of conjugated linoleic acid (CLA) that depress milk fat synthesis of short and medium chain fatty acids (FAs) in the mammary gland, and causes a reduction in milk fat content and yield (Chouinard et al, 1999;Baumgard et al, 2000). Abomasal infusion of pure isomers of CLA by Baumgard et al (2000) identified the trans-10, cis-12 CLA as the main responsible isomer for the milk fat depression (MFD).…”