Five sheep with rumen and abomasal cannulae were offered three diets sequentially in the order:
control (C) pellets (lucerne hay-oat grain: 60/40, w/w), control plus unprotected tuna oil (UTO
pellets), and control plus tuna oil protected (casein-formaldehyde matrix) against ruminal
biohydrogenation (PTO pellets). In supplemented diets, tuna oil constituted 3% (w/w) of total dry
matter (DM), and each supplement was fed for 12 days, with 9 days allowed between the two ®sh
oil feeding periods to minimise carry-over effects. Daily DM intake was 78538 g/head during the
control period. It was signi®cantly reduced by UTO feeding (6.2%,P<0:05) but not PTO feeding.
The level of EPA in the abomasum during PTO feeding was double that measured during UTO
feeding (1.30 versus 0.61% of FA, P<0:05). The level of DHA in the abomasum did not
signi®cantly differ between UTO and PTO feeding periods. Both tuna oil supplements signi®cantly
increased the levels of 18:1 trans and that of a fatty acid derivative identi®ed as 10-hydroxystearic
acid (10-HSA) in both the rumen and abomsum. Tuna oil supplementation also altered the fatty acid
composition of plasma lipid fractions and 10-HSA was solely incorporated into plasma free fatty
acids. This study indicates that substantial protection of tuna oil against ruminal hydrogenation
inhibited reduced feed intake, but increased the proportion of 18:1 trans isomer and fatty acids
derivatives (10-HSA), which indicate interference with metabolism in the rumen.#2001 Published
by Elsevier Science B.V.
Keywords:Abomasum; Rum
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