Effects of fish oil and starch added to a diet containing sunflower-seed oil on dairy goat performance, milk fatty acid composition and in vivo δ9-desaturation of [13C]vaccenic acid

Abstract

The potential benefits on human health have prompted an interest in developing nutritional strategies for specifically increasing rumenic acid (RA) in ruminant milk. The aims of the present study were to (i) compare two dietary treatments with lipid supplements on milk yield and composition, (ii) measure the in vivo δ9-desaturation of vaccenic acid (VA) to RA using 13C-labelled VA and (iii) determine the effect of the dietary treatments on this variable. Treatments were 90g sunflower-seed oil (SO) per d or 60g sunflower-seed oil and 30g fish oil per d plus additional starch (SFO), in a grassland hay-based diet given to eight Alpine goats in a 2×2 cross-over design with 21d experimental periods. Milk yield and composition were similar between treatments. Goats fed SFO had higher milk 6:0-16:0 concentration, lower milk C18 concentrations and showed no effect on milk VA and RA, compared with SO. At the end of the experiment, intravenous injection of 15g [13C]VA followed by measurements of milk lipid 13C enrichment showed that in vivo 317 and 316% of VA was 9-desaturated into milk RA in the caprine with the SO and SFO treatments, respectively. The expression of genes encoding for 9-desaturase (or stearoyl-CoA desaturase; SCD1, SCD5) in mammary tissues and four milk 9-desaturation ratios were similar between treatments. In conclusion, the present study provides the first estimates of in vivo endogenous synthesis of RA (63-73% of milk RA) from VA in goats, and shows no difference between the two lipid supplements compared. © 2010 The Authors.