Effects of commercially available palmitic and stearic acid supplements on nutrient digestibility and production responses of lactating dairy cows

摘要

We evaluated the effects of commercially availablefatty acid (FA) supplements containing palmitic (C16:0)and stearic acid (C18:0) on nutrient digestibility andproduction responses of dairy cows. Thirty-six midlactation(146 ± 55 d in milk) multiparous Holsteincows were randomly assigned to twelve 3 × 3 balancedtruncated Latin squares, with 3 treatments and 2 consecutive35-d periods, with the final 5 d used for sampleand data collection. Treatments were (1) a control dietcontaining no supplemental FA (CON), (2) a controldiet supplemented with a commercially available C16:0supplement (PA), and (3) a control diet supplementedwith a commercially available C16:0 and C18:0 supplement(MIX). Supplements were fed at 1.5% dry matterand replaced soyhulls in CON. The statistical modelincluded the random effect of cow nested within squareand the fixed effects of treatment, period, square, andtheir interactions. Preplanned contrasts were (1) overalleffect of FA treatments [CON vs. the average ofthe FA treatments (FAT); 1/2 (PA + MIX)], and (2)effect of FA supplement (PA vs. MIX). Treatment hadno effects on dry matter intake, body weight, or bodyweight change. Compared with CON, FAT decreaseddigestibilities of total FA and 18-carbon FA but did notaffect dry matter and neutral detergent fiber digestibility.Compared with MIX, PA increased dry matterand neutral detergent fiber digestibilities by 3.6 and 4.8percentage units, respectively. The PA also increasedtotal FA and 18-carbon FA digestibilities but did notalter 16-carbon FA digestibility compared with MIX.Using a Lucas test, we estimated apparent digestibilitycoefficients of 0.768 and 0.553 for the PA and MIXsupplements, respectively. Compared with CON, FATincreased milk yield and tended to increase energy-correctedmilk, but did not affect yield of milk fat or milkprotein. The PA increased energy-corrected milk andmilk fat yield but had no effect on milk protein yieldcompared with MIX. Our results indicate that dairycows producing around 45 kg of milk respond betterto a FA supplement enriched in C16:0 compared witha supplement containing both C16:0 and C18:0, whichis likely due in part to PA increasing FA and neutraldetergent fiber digestibility compared with MIX.