Partial replacement of corn grain with calcium salts of fatty acid in the concentrate fed to grazing primiparous and multiparous dairy cows

Abstract

The effects of the partial replacement of corn grain with calcium salts of unsaturated fatty acids (CSFA) on milk yield and composition, milk‐fatty acid profile and parameters linked to body lipid mobilisation were examined in 32 multiparous (MC) and 18 primiparous (PC) grazing cows in early lactation. Cows grazed a lucerne pasture and received a concentrate composed (DM basis) of 4.5 kg day‐1 of ground corn grain and 0.4 kg day‐1 of fish meal (Control) or similar to Control but replacing 1.8 kg of corn grain with 0.8 kg of CSFA (Fat). Pasture (14.3 kg cow‐1 day‐1), total dry matter intake (18.5 kg cow‐1 day‐1) and total energy intake (32.6 Meal NEL (net energy of lactation) cow‐1 day‐1) were not affected by dietary treatments or parity. Total energy consumed from the concentrates averaged 10.4 Meal NEL cow‐1 day‐1. Milk yield was increased in Fat on PC (20.4 versus 22.2 kg day‐1) but no effects were detected on MC. Milkfat concentration was reduced (‐2.4 g kg‐1) by Fat (P < 0.02). Fat‐corrected milk (24.5 versus 21.2 kg day‐1) and milkfat yields (0.93 versus 0.76 kg day‐1) were decreased by feeding CSFA on MC, with no effects on PC. Milk protein content was increased (31.9 versus 33.0 g kg‐1) in MC but decreased (32 versus 30.9 g kg‐1) in PC by CSFA. The lower fat‐corrected milk and milkfat yields in MC fed Fat lead to a higher (P < 0.05) estimated energy balance (6.27 Meal NEL day‐1) compared to Control (1.11 Meal NEL day‐1) cows, but changes in body weight gain (0.03–0.11 kg cow‐1 day‐1) were not detected. In PC, body weight was reduced (‐0.185 kg cow‐1 day‐1) and this affect was not reduced by feeding unsaturated CSFA. Plasma concentration of non‐esterified fatty acids was higher in PC than MC and not affected by CSFA either before (basal) or after the injection of a lipolytic agent (isoproterenol). Plasma concentration of glucose, urea and triglycerides were not affected by treatment or parity. Plasma cholesterol concentration was similar between PC and MC cows and higher in CSFA treatments. Concentration of de novo syn‐thesised fatty acids (C4.0 to C14.1) were decreased and that of unsaturated long chain FA (C18:1, C18:2 and C18:3) was increased by supplemental CSFA. Milkfat content of conjugated linoleic acid (cis‐9, trans‐11, CLA) was increased (+0.23 g 100 g‐1) by CSFA only in MC. The partial replacement of corn grain by unsaturated CSFA depressed fat‐corrected milk yield and improved the estimated energy balance in MC without changes in parameters linked to body lipid mobilisation. The health value of the milk for the consumer was improved through a reduction in the hypercholesterolemic fraction of milkfat and the increase in milk CLA content. PC responded to unsaturated fat feeding through an increase in milk production without changes in fat‐corrected milk. Supplemental fat did not reduce parameters linked to body lipid mobilisation. More studies are needed involving grazing PC to better understand the potential benefits of unsaturated fat feeding in early lactation.