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Identification of optimum feeding and management strategies to deliver CLA-enriched caprine milk

The aims were, in dairy goats: i) to study feeding strategies to maximize milk CLA, ii) to evaluate the effect of feeding Vitamin E on milk fatty acid (FA) profile and sensory properties of CLA-rich cheeses (see ETIP 36839), and iii) to yield milk to make CLA-rich cheese for clinical evaluation in humans (see ETIPs 36846 and 36847). Three successive studies have been conducted to evaluate 16 different feeding strategies (in comparison with previous data obtained on 26 other diets, Int Dairy Fed, 2005, 0501/part 5: 297-304).

The first feeding experiment was performed on 84 goats receiving one of 7 diets, to determine how forage/concentrate ratio and Vit E interact with linseed oil supplementation, and if extruded linseeds are efficient, compared to free oil, to increase milk CLA.

The main results were:
- Decreasing forage/concentrate ratio increased milk 10:0 to 14:0 and trans10-18:1 (% of total FA), did not change cis9,trans11-CLA (rumenic acid, RA), and decreased 18:0 and 18:3n-3 %;

- Linseed oil supplementation increased milk fat yield and the % of 18:0, 18:3n-3 and several trans isomers of 18:1 and conjugated or non-conjugated 18:2, and decreased 10:0-16:0 and 18:2n-6 %. Increases of trans11-18:1 (vaccenic acid, VA) (from 0.9 to 7.5 %) and of RA (from 0.5 to 3.2 %) were large, as were decreases in atherogenicity index (3.9 to 1.8) and n-6/n-3 ratio (4.3 to 1.3);

- Vit E addition increased milk fat yield, 18:0 %, and several trans isomers of conjugated or non-conjugated 18:2 and decreased 10:0-16:0 %. The increase of trans11-18:1 (from 7.6 to 8.8 %) was significant although RA was not changed (3.2 %);

- Extruded linseeds, compared to free linseed oil, decreased 16:0 %, trans11-18:1 and RA (from 3.1 to 2.1 %) and increased milk protein content and 18:0, 18:2n-6, 18:3n-3 and cis9,trans13-18:2 %, and the n-3/n-6 ratio (from 0.9 to 1.3).

The results after either 5 or 9 wk of dietary treatments were similar, showing that the responses were stable for at least 2 months.

The plasma FA profile of the goats changed mostly in the same direction than observed for milk FA.

The second feeding experiment was performed on 84 goats receiving one of 7 diets to determine:
- How to maximize the milk CLA by combined effects of forage/concentrate ratio and high doses of either linseed oil (LO) or sunflower oil (SO)?

- If the extrusion of a mixture of linseeds and sunflower seeds is efficient?

- The kinetics of the response of CLA to dietary changes, compared to published data in cows in which CLA response is often unstable.

Milk fat content was decreased by low (LF) vs. high forage (HF) diet, and strongly increased by lipid supplementation. Milk rumenic acid % rapidly increased to reach its maximum after 2 wk of lipid supplementation. The highest level (5%) was achieved with HF + SO, whereas other diets were around 3%. LO supplementation decreased 10:0 - 16:0 and increased 18:0, 18:3 n-3, and trans-18:1 and trans-18:2 isomers. SO supplementation to HF diet induced the greatest decrease in 10:0 - 14:0 and increased cis-9 18:1, trans10 + trans11-18:1, rumenic acid and 18:2 n-6. Extruded seeds maximized 18:0 and 18:3 n-3. The sum of non-trans11 18:1 and 18:2 was highest with LO, high with extruded seeds, medium with SO, and lowest with basal diets.

The third feeding experiment was done to supply control and CLA-enriched milk for cheese making for studies in humans. Forty-eight goats received a diet based on alfalfa hay and supplemented, or not, with sunflower oil and Vit E. Milk CLA was increased from 0.3 to more than 4% of total FA (x13-fold) by lipid supplementation.
A second objective of this trial was to compare milk FA composition, and responses to lipid supplementation, in goats differing by their genotype at the alpha-S1 casein locus (24 high- and 24 low-genotypes).

In parallel, a retrospective analysis was done on milk FA composition from 33 Low- and 38 High-genotype goats. Low-genotype goats had a much lower (-6.8g/kg) milk fat content and much less medium-chain FAs, less stearic acid, more palmitic, oleic, linoleic and rumenic acid than High-ones. Furthermore, the delta-9 desaturation ratios of milk FAs were higher in Low-genotype goats for 10:0, 14:0, 17:0, 18:0, trans11-18:1 and trans13-18:1, strongly suggesting that delta-9 desaturase activity was increased, probably to insure the constancy of milk fat melting point despite the decrease in the synthesis of medium-chain FAs.

In conclusion, the goat largely differs from the cow in its response to dietary factors for milk fat yield and FA profile. The goat is a very good, repeatable and sustainable responder for milk CLA. High forage diets supplemented with vegetable oil rich in polyunsaturated FA and Vit E, are suitable to yield high-CLA milk for cheesemaking.

Reported by

Institut National de la Recherche Agronomique (INRA)
Clermont-Theix Research Centre, Herbivore Research Unit,
63122 Saint Genes Champanelle