The effect of feeding diets markedly differing in the proportion of grass and maize silages on bovine milk fat composition

Ten Czech Pied cows in the mid-lactation stage were fed diets based on grass silage and maize silage. The composition of milk fats differed. The proportions of even-chain saturated fatty acids (SFAs) up to C-14:0 were insignificant and the content of C-16:0 was significantly higher (P < 0.05) when feeding a diet based on maize silage, while the proportions of the individual polyunsaturated fatty acids (PUFAs) were significantly (except for C 18:2) higher when feeding a diet based on grass silage. The total SFA proportions were 67.60 and 62.93% (P < 0.05) of maize and grass silages, respectively, while an opposite relation was observed for the sum of PUfAs (3.56 and 4.74%; P < 0.001). Feeding of grass silage resulted in a significantly lower proportion of hypercholesterolaemic fatty acids C-12:0' C-14:0 and C-16:0 (49.38 and 44.98%, respectively; P < 0.05) and in lower values of the atherogenic index (3.03 and 2,44; P < 0.05). Thus, the results could be used for the improvement of milk fat composition.