Effect of mixed oil on C 18-fatty acid and conjugated linoleic acid pro fi les in rumen fl uid and blood plasma of cattle

The experiment was conducted to determine the effect of mixed oil on C18-fatty acid and CLA profi les in rumen fl uid and plasma of Yanbian cattle by adding different levels of the mixed oil to concentrate. The contents of propionate and C18:1 were increased in rumen fl uid by adding mixed oil. In plasma, the contents of C18-fatty acids in experimental groups were all signifi cantly higher than in the control group; c9, t11-CLA increased at 6 h, t10, c12-CLA increased at 0, 9, 12 h. Enhancing CLA contents of rumen fl uid and plasma through feeding 4% mixed oil in the diet seems to be the optimal level.


INTRODUCTION
Research efforts have been intensifi ed to increase the content of conjugated linoleic acid (CLA) in meat and milk products due to its potential health benefi ts such as cancer prevention and multiple important physiological effects.It has been reported that an important factor affecting CLA products is the concentration of C 18:2 in the diet.Supplementation of vegetable oil to the diet has proved to affect the CLA content of ruminant products.We added a mixed oil containing soya bean oil, saffl ower oil and sunfl ower oil, all of which are abundant in C 18:2 .This study was conducted to examine the effect of different levels of the mixed oil on C 18fatty acid and CLA profi les in rumen fl uid and blood plasma in order to fi nd the optimal supplement level for increasing the contents of CLA in Yanbian cattle.YAN C.G. ET AL.

MATERIAL AND METHODS
Three ruminally fi stulated Yanbian cattle (body weight, 275±20 kg) were used in an experiment conducted in a 4×3 incomplete Latin square design with 4 periods and 3 dietary treatments in each period.Each period lasted 12 d.The basal diet of each animal included per day, kg: concentrate 4.05, maize silage 6, and rice straw 1.The nutritional composition of the basal diet is presented in Table 1.The diets of experimental groups were supplemented with 4, 5, and 6% (concentrate basis) mixed oil, respectively, added to the concentrate by pouring it on and mixing at feeding to ensure equal distribution in the ration.The control group was not fed the mixed oil.The cattle were fed twice daily (06.30 and 18.30 h).The mixed oil was composed of, %: soya bean oil 55, saffl ower oil 25 and sunfl ower oil 20.Proportions (% of total) of palmitic acid (C 16:0 ), stearic acid (C 18:0 ), oleic acid (C 18:1 ), linoleic acid (C 18:2 ) and linolenic acid (C 18:3 ) as major fatty acids for the mixed oil were 7. 65, 3.12, 13.16, 53.27 and 0.31, respectively.On day 10, 100 ml rumen fl uid was collected from various sites of the rumen at 0, 3, 6, 9 and 12 h post feeding and strained through four layers of gauze.A 0.5 ml aliquot of rumen fl uid was mixed with 0.2 ml 25% metaphosphoric acid.The mixture was centrifuged at 10,000 g for 10 min at 4°C, and the supernatant was used to determine the composition of VFA by using a Hewlett-Packard HP6890 GC system equipped with a capillary column (HP-INNOWax column, 30m×320 μm×0.50 μm, Hewlett-Packard).The remainder of rumen fl uid was stored at -20°C and freeze dried.Fatty acids were analysed according to the method of Raes et al. (2002).The fatty acid methyl esters were analysed by a GC System equipped with a capillary column (DB-23 column, 60 m × 249 μm × 0.25 μm, Hewlett-Packard).The injector and detector temperature was maintained at 250°C, respectively.The initial column temperature was 180°C (held for 10 min), and then increased by 4°C/min to 220°C (held for 15 min).Ultra pure helium was used as the carrier gas.On day 12, 30 ml blood samples were collected from the jugular vein at 0, 3, 6, 9 and 12 h post feeding and then centrifuged immediately at 3,000 g for 10 min.The supernatants (plasma) were transferred into 15 ml screw-cap tubes and were kept frozen at -70°C until analysed.Analysis of plasma fatty acids followed the same procedure as that of the rumen fl uid analysis.Data collected from the experiments were subjected to analysis of variance (ANOVA) using the SAS (1996) software.Means were separated by Duncan's multiple range test.

Table 1 .
The nutritional composition of the basal diet, %, DM basis

Table 2 .
Concentration of VFA in rumen fl uid, mmol/l

Table 3 .
Contents of C 18 -fatty acids in rumen fl uid, mg/g of fatty acids