Enrichment of conjugated linoleic acid (CLA) in the eggs of laying hens fed pure isomers of CLA or vaccenic acid

Kirjoittajat

• Edison Muma University of Helsinki, Department of Animal Science, PO Box 28, 00014 Helsinki
• Samu Palander Seinäjoki Polytechnic, Ilmajoki Institute of Agriculture, Ilmajoentie 525, FIN-60800 Ilmajoki
• Matti Näsi University of Helsinki, Department of Animal Science, PO Box 28, 00014 Helsinki
• Mikko Griinari University of Helsinki, Department of Animal Science, PO Box 28, 00014 Helsinki

DOI: https://doi.org/10.33354/smst.76778

Avainsanat:

conjugated linoleic acid, vaccenic acid, laying hens, Δ-9 desaturase

Abstrakti

Conjugated linoleic acid (CLA) is a complex mixture of positional and geometric conjugated isomers
of linoleic acid. Dairy products are the major dietary source of CLA and cis-9, trans-11 CLA (9,11
CLA) is the predominant isomer resulting from the specific metabolism of feed derived fatty acids in
the rumen. Recent studies suggest endogenous synthesis of CLA by action of Δ-9 desaturase on trans-
11 18:1 fatty acid (vaccenic acid, VA) is more important than ruminal production. In view of potential
human health benefits, several studies have attempted to enrich eggs with CLA by supplementing the
diets of laying hen with mixtures of CLA. This has resulted in marked enrichment but also negative
effects on egg quality and loss of hatchability of the eggs with concurrent increase in saturated fatty
acid content in egg yolk. Such changes are consistent with Δ-9 desaturase inhibition especially associated
with the presence of the trans-10, cis-12 CLA isomer (10,12 CLA) in the CLA mixtures. It is
therefore worthwhile to determine which of the major CLA isomers present in the CLA mixtures, 9,11
CLA or 10,12 CLA, is associated with the negative effects on egg quality. This was done by supplementing
the diets of laying hen with relatively pure forms of 9,11 CLA and 10,12 CLA. Furthermore,
using relatively pure forms of 9,11 CLA and 10,12 CLA allowed us to determine the transfer efficiency
of 9,11 CLA and 10,12 CLA into egg yolk. In addition, endogenous conversion of VA to 9,11
CLA in hens and deposition in egg yolk was examined.
Experimental treatments consisted of diets supplemented with 0, 0.5, 1.0 and 1.5 g/d of CLA or
VA. CLA isomer content (% of total fatty acids) of the materials was 83 and 7% (9,11 CLA), 9 and
85% (10,12 CLA), 35 and 35% (Mix CLA) of 9,11 CLA and 10, 12 CLA, respectively. VA was supplied
in the form of dehydrated hydroxy stearic acid with trans-11 C18:1 content of 28%. The other
major isomers in this product were cis-11, trans-12 and cis-12 C18:1 (28, 11 and 11%, respectively).
There were three hens in each treatment and experimental diets were fed for 21 days. When diets
were supplemented with 9,11 CLA, 10,12 CLA and Mix CLA the transfer efficiencies (percentage
of dietary CLA recovered in the egg) of 9,11 CLA and 10,12 CLA in egg yolk total lipids were 21 and
<1%, 24 and 12%, 20 and 9%, respectively. Dietary VA was efficiently converted to 9,11 CLA and
deposited in the yolk. The slope of linear regression of VA plus 9,11 CLA versus 9,11 CLA in the egg
yolk total lipids represents an estimate of the average conversion over the range of VA intakes studied.
In this study 74% of VA available for desaturation was converted to 9,11 CLA. The transfer efficiency
of VA (percentage of dietary VA recovered as VA plus 9,11 CLA in the egg) was 14%. Dietary vaccenic
acid in hens is efficiently converted to 9,11 CLA, but the overall efficiency of dietary VA use for
CLA enrichment is quite low. Further studies examining the limitations of VA transfer to the liver and
availability for conversion by Δ-9 desaturase should be examined.