The use of rapeseed screenings in diets for lactating cows and subsequent effects on milk yield and composition

This trial was to determine the effect of dietary rapeseed screenings on milk production, milk composition, and feed intake of lactating dairy cows. Pelleted rapeseed screenings were fed at 0, 7, and 14% of diet DM. Assignment of 36 multiparous Holstein cows was based upon parity and previous lactation performance. The experimental period was from parturition through wk 16 of lactation. The control ration had 3.1% ether extract, whereas the ration with 14% rapeseed screenings had 5.4% ether extract. The rapeseed screenings contained 52.2% of C18:1 and 24.2% of C18:2 as percentage of total fatty acids. There were no significant effects of dietary treatment on milk yield or feed intake. There were significant increases in milk fatty acids C18:1 and C18:2 for cows consuming the diets with rapeseed screenings. Treatment did not significantly affect milk protein percentage as measured by Kjeldahl N or by the infrared method. Increased unsaturated fatty acids in the milk of cows fed rapeseed screenings had no apparent effect on infrared fat analysis. There was no interaction of treatment and milk fat analysis method (infrared versus Babcock). Dietary treatment did not affect blood serum nonesterified fatty acid concentrations over the 16-wk period. In conclusion, rapeseed screenings, fed at levels up to 14% of the diet, did not affect milk yield, milk protein, or milk fat percentage but did change milk fatty acid composition.