EFFECTS OF FEEDING RAPESEED PRODUCTS TO DAIRY-COWS ON THE HARDNESS OF MILK-FAT - MILCHWISSENSCHAFT

A balanced two-period changeover design involving 42 lactating dairy cows and 7 feeding variants (12 observations per variant) was performed to study the influence of the amount and technical treatment of rapeseed on milk fat hardness by considering feed intake, digestion of nutrients, milk yield and composition chemically (iodine value, fatty acid and triglyceride composition) and physically (penetration, melting profile, solid fat content). The 7 feeding variants consisted of approximately 70% identical proportions of basal ration and roughly 30% concentrate, in which wheat was isoenergetically replaced by rapeseed oil This was fed in amounts of 275 and 550 g as such and in form of ground and pelleted rapeseed (550 g only). Crude fat intake was, thus, maximally 940 g, corresponding to approximately 5% of the total dry matter. A further variant contained an amount of stearic acid and glycerol which was triglyceride-equivalent to 275 g rapeseed oil. The control diet containing no rapeseed oil vielded an extremely hard milk fat. 275 g Rapeseed oil in the diet led to a drastic change of all hardness parameters investigated. These suffice to meet the German legal spreadability requirements for butter. An increase in the amount of rapeseed oil to 550 g yielded a milk fat typical of summer feeding. Technical treatment of rapeseed influenced milk fat composition only (though characteristically) to a slight extent (e.g. more C18:2 with ground, more trans C18.1 with pelleted rapeseed). These differences produced, however, no marked effect on milk fat hardness. The practical importance of the results obtained is that all rapeseed oil variants impaired neither feed intake, digestion of nutrients nor the parameters of milk performance, compared with the control diet. Further, the milk fats obtained have not been found to differ from commercial butterfats as regards the 30 parameters studied, which is indicative of a normal fat metabolism due to the rations given to the cows.