January 25, 2010
Like hockey team managers at training camp selecting top prospects, Canadian dairy producers may soon be able to select cows with better potential for producing milk with higher levels of conjugated linoleic acid (CLA).
A University of Alberta study shows that dairy cows with a certain genetic makeup tend to be better than their herdmates at producing milk with CLA when fed a high-linoleic acid diet. This development comes as CLA and related vaccenic acid (VA) continue to generate excitement in research, health and food circles, based on indications of their health enhancing activity.
"Our findings are a very good start for accounting for the variation in CLA production that we see among different dairy cows," says Laura Clark, a researcher in the Department of Agricultural, Food and Nutritional Science who conducted the study for her master's degree. "This leads us down the path of being able to select away from the mediocre performers and toward the better performers, so dairy farmers aiming to increase CLA can have the ability to do that through genetic strategies."
nutrition strategies, such as supplementing dairy cow diets with plant oils high in linoleic acid - a type of fatty acid that ruminant animals convert into CLA. Prior to the U of A genetics study, the effect of the interaction of genetics with diet on fatty acid profile was still relatively unknown. "Our new findings show that opportunities exist for genetic improvement in this area," says Clark.
The study involved genotyping animals by extracting blood samples and conducting analysis. Four animals of each of three genotypes - 12 animals total - were selected to fit a study design aimed at drawing accurate comparisons of the effect of genetics combined with diet. The experimental design was a crossover study with 21 day periods and treatments that included low fat or high fat diet. A follow-up study was conducted with a commercial herd of over 200 animals and found similar results.
"We found that when dairy cows were fed a high-fat diet, certain cows tend to show a genetically superior ability to sustain production of CLA.
Importantly, the genetic variability in CLA production was only found with the high fat diet. "As a result, the opportunity uncovered here is to combine genetic strategies with a feeding program," says Clark.
The special diet served to provide substrate for an enzyme known to play a key role in CLA conversion. "We found if you don't challenge the enzyme then you're not going to see the differences in the individual animal's abilities."
In particular, the genotype group in the study labeled "AA" showed a tendency for greater activity of this enzyme and a corresponding greater conversion of the CLA precursor into CLA.
"If we had dairy operations that were specifically interested in producing dairy products that were CLA enriched, they could choose to select for this trait. To get the results, they would have to stimulate the animals by feeding a high fat diet, which is not the norm but past studies have shown there is potential to do this cost effectively."
Further CLA studies focused on genetics can help uncover further options, she says. "We don't think that this one enzyme or this one gene is the only factor. However we have shown that it's a very key factor, related to a lot of the variation. We suspect there are probably at least a couple more genetic factors that would account for more of the variation that we're seeing.
Reprintable with credit to the CLA Network.