K. A. Ellis,*1 G. Innocent,* D. Grove-White,†
P. Cripps,† W. G. McLean,‡
C. V. Howard,§ and M. Mihm#
*Division of Animal Production and Public Health,
University of Glasgow Veterinary School, Bearsden
Road, Bearsden,
Glasgow, G61 1QH, UK.
Abstract
During a 12-mo longitudinal study,
bulk-tank milk
was collected each month from organic (n = 17) and
conventional (n = 19) dairy farms in the United Kingdom.
All milk samples were analyzed for fatty acid
(FA) content, with the farming system type, herd production
level, and nutritional factors affecting the FA
composition investigated by use of mixed model analyses.
Models were constructed for saturated fatty acids,
the ratio of polyunsaturated fatty acids (PUFA) to
monounsaturated fatty acids, total n-3 FA, total n-6
FA, conjugated linoleic acid, and vaccenic acid. The
ratio of n-6:n-3 FA in both organic and conventional
milk was also compared. Organic milk had a higher
proportion of PUFA to monounsaturated fatty acids
and of n-3 FA than conventional milk, and contained
a consistently lower n-6:n-3 FA ratio (which is considered
beneficial) compared with conventional milk.
There was no difference between organic and conventional
milk with respect to the proportion of conjugated
linoleic acid or vaccenic acid. A number of factors
other
than farming system were identified which affected
milk FA content including month of year, herd average
milk yield, breed type, use of a total mixed ration,
and
access to fresh grazing. Thus, organic dairy farms
in
the United Kingdom produce milk with a higher PUFA
content, particularly n-3 FA, throughout the year.
However, knowledge of the effects of season, access
to
fresh grazing, or use of specific silage types could
be
used by producers to enhance the content of beneficial
FA in milk.
Keywords: fatty
acid, n-3 fatty acid, conjugated linoleic acid,
Organis farming.
