The influence of dietary rumen‐protected linoleic acid on milk fat composition,spreadability of butter and energy balance in dairy cows

The aim of this study was to determine the effects of a diet supplemented with rumenprotected linoleic acids (C18:2) on the composition of milk fat and the energy balance of dairy cattle during the first 15 wk of lactation. The 32 Holstein‐Friesian cows were allotted in two treatment groups; in the experimental group one‐third of the starch (relative to the control group) was substituted with protected fat on an energy basis. Milk samples from all cows were collected weekly from week 2 to 15 postpartum (p.p.). To analyze the milk fat composition milk samples from 16 cows in each group were collected from week 6 and 7 as well as from week 13 and 14 p.p. and were mixed together, respectively. Triglyceride analysis demonstrated an extensive use of depot fat in both cow groups at the beginning of the lactation period. However, calculated energy balance, triglyceride composition and back fat thickness showed that the usual deficit of energy intake in early lactation was significantly shortened in the experimental group by three weeks. In comparison with the control group the content of the saturated fatty acids (FAs) C12, C14 and C16 in the experimental group decreased by 17.3% at 6 to 7 wk and by 19.2% at 13 to 14 wk. The stearic acid content of milk fat was increased by 25.9% at 6 to 7 wk and by 27.7% at 13 to 14 wk in the experimental group. The content of cis Δ9 oleic acid was increased by 21.6% at 6 to 7 and by 30.3% at 13 to 14 wk, while the C18:2 FA content was doubled as compared with the control group. Thus besides the increase of the trans‐C18:1 FA (TFA) content the nutritional value of fats could be improved using the experimental fat supplement. The TFA content still remained within the range of variation of natural milk fats. Additionally the experimental fat intake led to a number of desired effects; an increase in the content of conjugated linoleic acids (cis Δ9, transΔ11) by 55.9% (6 to 7 wk) and by 97.1% (13 to 14 wk p.p.), respectively, and a decrease in the cholesterol level. Further, the butyric acid content increased relatively by more than 20%. The addition of this fat resulted simultaneously in a changed triglyceride composition with increased C50, C52 and C54 contents. Thus a markedly improved spreadability of the resulting butter might be expected.