Abstract
The present investigation was aimed to test whether α-linolenic acid (ALA) concentrations in the adipose tissue can be increased by linseed feeding of dry cows and whether ALA is preferentially mobilized during the catabolic phase after parturition. The second objective was the determination of the influence of mobilization on fatty acid composition of colostrum and mature milk. For this purpose, four groups of six cows were fed diets supplemented either with crushed linseed (rich in ALA; two groups) or sunflower seed (rich in linoleic acid (LA)) or a 1:1 mixture of both for 6weeks. This supplementation was either kept post partum or switched shortly before calving from linseed or the mixture to sunflower seed. The post partum experimental period lasted for another 40d. Samples of blood were obtained in weeks −6, −2, 3 and 6 pre/post calving, those of backfat adipose tissue in weeks −2 and 6 pre/post calving (by biopsy) and milk samples on days 1, 2, 10, 20, 30 and 40 of lactation. Clear changes over time occurred in blood plasma metabolites and hormones as well as in body weight, body condition scores and backfat thickness, especially during the transition before and after calving. Milk yield and composition showed the typical time trends as well. Proportions of long-chain polyunsaturated fatty acids in the colostrum compared to the mature milk were clearly higher. This appeared similarly in all groups and was not influenced by the oilseed treatment. Compared with the physiological time effects, the effects of the oilseed treatments were weak. It was possible to load the adipose backfat tissue with ALA by supplementing linseed in the dry period, but the magnitude of this increase was small. Milk fat profile was not affected accordingly, although the changes found in adipose tissue post partum suggested the preferential mobilization of ALA during early lactation. Supplementing sunflower seed instead of linseed in the dry period did not elevate LA proportion in adipose tissue nor affected linoleic acid in milk. By contrast, direct transfer of LA, and especially of ALA, from feed to milk happened when sunflower seed or linseed was fed in the lactation period of the experiment. Overall this suggests that strategies aiming at changing n−3 fatty acid concentrations in milk fat composition by loading the adipose tissue of dry cows with ALA are not effective.
Leiber, F