The effect of rapeseed oil and palm oil supplement and milking frequency on milk yield and milk fat quality

Abstract: Milk fat is an important feature in many different milk products and other foodstuffs and it is often crucial for the dairy plants that the milk fat is stable for different manufacturing processes. Lipolysis is the enzymatic degradation of fat and is the one of the causes for an elevated amount of free fatty acids (FFA) in milk. Further, the change in fatty acid (FA) composition in milk can affect the stability of the product and also the manufacturing process. Both internal and external factors, at farm level or at the dairy plants can affect both FA composition and content of FFA. Milking frequency (MF=number of milkings per cow and day) and the composition of feed are two examples of factors generally performed at farm level. The objective of the present study was to evaluate how FA composition of milk and amount of FFA are influenced by two different ingredients supplemented to concentrate. The added ingredients were palm oil and rapeseed oil. The effects of the two fat supplements were evaluated individually but also during a higher MF to detect if a change in MF can have an effect on milk fat when a specific fat supplement is added in the diet. In total 30 dairy cows, both primiparous (n=16) and multiparous (n=14) of the breeds Swedish Holstein (n=14) and Swedish Red (n=16) were divided into three groups assigned different concentrate in diet; no fat supplement, palm oil supplement and rapeseed oil supplement. The experiment was divided into a nine days adaption period and then five weeks of experimental feeding. Dry matter intake (DMI) and daily milk yield (MY) were registered throughout the experimental period, both during adaption period and experimental feeding. Milk samples were collected for two days, during morning and evening milking at three occasions during the experiment; the last two days during the adaption period, the 4th and 5th week during experimental feeding. The last sampling was performed during the treatment with an increased milking frequency (IMF) where milk samples were taken four times per day. Milk samples were analyzed for milk composition (fat, protein and lactose), milk FA profile, amount of FFA and milk fat globule size (MFG). Results from present experiment show, as expected, that a higher MF resulted in a higher MY and elevated concentration of FFA in milk. Unexpected was that an IMF did not have a significant effect on size of MFG. However it was observed a tendency for size of MFG that is worth mentioning. Some individual FA were affected by MF where the content of C4:0 was increased and C12:0 and C18:3 (n-6) were decreased when the cows were milked four times per day instead of two times per day. Further it was demonstrated that an increased MF together with a change in diet will not affect the milk fat composition and FA profile in milk. The same results was seen for content of FFA and size of MFG. This present study has also confirmed previous findings that the FA compositions in feed will not be the same as the outcome of the composition in milk. Milk components yields were not affected by diet but cows fed palm oil diet (P) had lower content of fat and protein compared to control diet (C). Diet did not have an impact on content of FFA and size of MFG. Both diets with supplemented fat had lower concentrations of shorter FA (≤ C14) and SFA while content of mono-unsaturated fatty acids (MUFA) and poly-unsaturated fatty acids (PUFA) were higher compared to C diet. Further, as expected cows fed rapeseed oil diet (R) had the highest yield of MUFA and PUFA in milk, where the individual FA; C18:1 (n-9), C18:2 (cis9 trans11, CLA) and C18:3 (n-6) were found in higher rapeseed oil did not influence the milk in a negative way, which has been discussed in former studies. Rapeseed oil as a fat supplement in concentrate could therefore be a good alternative to palm oil in the future.