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Abstract. The function of the brain is to exert centralized control over the other internal organs and tissues of the body. Thus, the objective of our studies was to evaluate changes in the concentration of fatty acids (FAs), cholesterol (CHOL), cholest-4-en-3-one (CHOL-4-3), tocopherols, malondialdehyde (MDA) and fatty aldehydes in the brains of lambs fed supplemented diets. Thirty male Corriedale lambs with a body weight of 30.5 ± 2.6 kg were allotted to five groups of six lambs and housed individually. After the preliminary period, for 35 days the animals were fed a diet containing 3 % rapeseed oil (RO) (the RO diet), a diet enriched with 2 % RO and 1 % fish oil (FO) (the FO diet) or the diets with combined addition of 2 % RO, 1 % FO, 0.1 % carnosic acid (CA) (the CA diet) and 0.35 ppm Se as the selenized yeast (SeY) (the CASeY diet) or selenate (SeVI) (the CASeVI diet). The CASeVI diet most efficiently increased the accumulation of FAs (including unsaturated FAs), CHOL-4-3 and fatty aldehydes in the lamb brain. This diet most effectively decreased the concentration of CHOL and MDA in the brain. The CASeY diet showed a different impact on the level of FAs, CHOL, CHOL-4-3, tocopherols, MDA and fatty aldehydes in the brain as compared with the CASeVI diet. The CA diet reduced the concentration of CHOL-4-3, the sums of fatty aldehydes, FAs, atherogenic-and thrombogenic-saturated FAs in the brain compared with the CASeVI diet; the CA diet most effectively increased the value of polyunsaturated FA (PUFA) peroxidation index in the brain. The RO diet most efficiently increased the concentration of CHOL and values of the ratios of saturated FAs to PUFAs and long-chain n-6PUFAs to long-chain n-3PUFAs in the brain.The current studies provide new useful information for nutritionists carrying out further investigations aimed at improving farm-animal health, growth performance, reproductive system and the nutritional quality of feed for ruminants.

The influence of seleno-methionine (Se-Met) added to an ovine ruminal fluid containing a-linolenic acid (a-LNA) on the profile of fatty acids (FA) was investigated. The fluid was incubated in vitro at 39°C under CO 2 either alone (the control ruminal fluid; RF) or with a-LNA (1.67 mg/mL) or with a combination of a-LNA with either a low (1.25 mg/mL) or high Practical applications Selenium and polyunsaturated fatty acids n-3 (PUFAn-3) are very important for human health and nutrition. Recent studies documented that a higher content of mono-conjugated isomers of a-linolenic acid (a-LNA) in diets reduced the abundance of PUFAn-3 in the brain, liver and heart of experimental animals. Due to the increasing world population, overfishing of the seas and usually low concentrations of PUFAn-3 and essential trace elements (like selenium) in animal products, there is a demand for better methods of feeding livestock. Considering the above, it was desirable to study the extent to which dietary seleno-compounds (like seleno-methionine) may contribute to concentrations of mono-conjugated a-LNA (C-a-LNA) isomers, as C-a-LNA isomers may perturb the PUFA balance (or imbalance) in tissues of animals and humans. Moreover, further studies are needed to determine if dietary seleno-compounds, a-LNA and C-a-LNA isomers also induce changes in concentrations of fatty acids, especially PUFAn-3, in tissues of lambs.