Dietary supplements of whole linseed and vitamin E to increase levels of alpha-linolenic acid and vitamin E in bovine milk

摘要

The potential to increase the concentrations of n-3 polyunsaturated fatty acids (PUFAs) in milk fat was investigated by studying the effects of feeding a xylose-treated, whole cracked linseed supplement (rich in alpha-linolenic acid) to dairy cows. Also the effect of increasing the dietary intake of vitamin E on the vitamin E status of milk was investigated. The effect of pasteurisation on milk fatty acid composition was also examined. Using a 3 X 2 factorial design, a total of 60 Holstein dairy cowswere fed a total mixed ration based on grass silage supplemented with one of three levels of whole cracked linseed (78, 142 or 209 g centre dot kg~(-1) diet dry matter (DM); designated LL, ML or HL, respectively) in combination with one of two levels ofadditional dietary vitamin E intake (6 or 12 g vitamin E centre dot animal~(-1) centre dot day~(-1); designated LE or HE, respectively). Increasing lipid supplementation reduced (P < 0.01) diet DM intake and milk yield, and increased (P < 0.001) the overall content of oleic, vaccenic, alpha-linolenic and conjugated linoleic acids, and total PUFAs and monounsaturated fatty acids (MUFA). Myristic and palmitic acids in milk fat were reduced (P < 0.001) through increased lipid supplementation. While alpha-linolenic acid concentrations were substantially increased this acid only accounted for 0.02 of total fatty acids in milk at the highest level of supplementation (630 g alpha-linolenic acid centre dot animal~(-1) centre dot day~(-1) for HL). Conjugatedlinoleic acid concentrations in milk fat were almost doubled by increasing the level of lipid supplementation (8.9, 10.4 and 16.1 g centre dot kg~(-1) fatty acids for LL, ML and HL, respectively). Although milk vitamin E contents were generally increasedthere was no benefit (P > 0.05) of increasing vitamin E intake from 6 to 12 g centre dot animal~(-1) centre dot day~(-1). The fatty acid composition of milk was generally not affected by pasteurisation.