Effect of enrichment the summer feeding ration for milking cows with mixture of fish oil and rapeseed oil on selected rumen parametres and milk fatty acid profile

Two trials were conducted. In trial I three lactating Polish Holstein-Friesian (PF) cows fitted with rumen cannulae were used in a 3 x 3 Latin square design. In each feeding cycle animals were offered one of three following diets: (1) without supplementation (C diet - control), (2) C diet supplemented with fish and rapeseed oils blend 1:1 (FR diet), and (3) C diet supplemented with commercial protected fat (CPF diet). In trial II, ten lactating PF cows were offered C diet, and another ten - FR diet. In both trials fat supplements constituted up to 4% of the diet dry matter. FR diet strongly affected the fatty acid composition of rumen fluid and milk of cows. Content of oleic acid and other MUFAs increased, while that of total SFAs dropped in the rumen and, in both trials, in milk. The FR diet led to increase in the c9 t11 CLA (conjugated linoleic acid) isomer content of milk in both trials. In trial II the t10 c12 CLA concentration of milk increased in cows fed the FR diet. It is evident that during the summer feeding based on fresh green forage, good results regarding milk fatty acid content can still be improved by feeding rapeseed oil and fish oil.