Effects of forage type, forage to concentrate ratio, and crushed linseed supplementation on milk fatty acid profile in lactating dairy cows.

ABSTRACT

The effects of an increasing proportion of crushed linseed (CL) in combination with varying forage type (grass or corn silage) and forage to concentrate ratio (FC), and their interactions on milk fatty acid (FA) profile of high-producing dairy cows was studied using a 3-factor Box-Behnken design. Sixteen Holstein and 20 Swedish Red cows were blocked according to breed, parity, and milk yield, and randomly assigned to 4 groups. Groups were fed different treatment diets formulated from combinations of the 3 main factors each containing 3 levels. Forage type (fraction of total forage dry matter, DM) included 20, 50, and 80% grass silage, with the remainder being corn silage. The FC (DM basis) were 3565, 5050, and 6535, and CL was supplied at 1, 3, and 5% of diet DM. Starch and neutral detergent fiber content (DM basis) of the treatment diets ranged from 117 to 209 g/kg and 311 to 388 g/kg, respectively. Thirteen treatment diets were formulated according to the Box-Behnken design. During 4 experimental periods of 21 d each, all treatment diets were fed, including a repetition of the center point treatment (50% grass silage, 5050FC, 3% CL) during every period. Intake, production performance, and milk FA profile were measured, and response surface equations were derived for these variables. Shifting from 80% grass silage to 80% corn silage in the diet linearly increased dry matter intake (DMI), net energy for lactation (NE(L)) intake, cis-9,cis-12-C182 (C182n-6) intake, and milk yield, and linearly decreased cis-9,cis-12,cis-15-C183 (C183n-3) intake and milk fat content. Shifting from a high forage to a high concentrate diet linearly increased DMI, NE(L) intake, C182n-6 intake, and milk yield, and decreased milk fat content. Supplementation of CL linearly increased C183n-3 intake, but had no effect on DMI, NE(L) intake, milk yield, or milk fat content. Shifting from 80% grass silage to 80% corn silage linearly increased proportions of trans-10-C181 and C182n-6 in milk fat, whereas the proportions of trans-11,cis-15-C182 and C183n-3 linearly decreased. Significant interactions between CL supplementation and FC were found for proportions of trans-10-C181, trans-15-C181, cis-15-C181, trans-11,cis-15-C182, and C183n-3 in milk fat, with the highest levels achieved when the diet contained 5% CL and a 3565FC ratio. The effect of supplementing CL on several milk FA proportions, including C182n-6 and C183n-3, depends significantly on the FC ratio and forage type in the basal diet.