Milk production responses to altering the dietary ratio of palmitic and oleic acids varies with production level in dairy cows

摘要

We evaluated the effects of altering the dietaryratio of palmitic (C16:0; PA) and oleic (cis-9 C18:1;OA) acids on production responses of cows with awide range of milk production (32 to 65 kg/d) in acrossover design experiment with a preliminary period.Thirty-two multiparous Holstein cows (144 ± 54 d inmilk) were assigned randomly to a treatment sequence.Treatments were diets supplemented with fatty acid(FA) blends (1.5% of diet dry matter) that provided80% C16:0 + 10% cis-9 C18:1 (PA) and 60% C16:0 +30% cis-9 C18:1 (PA+OA). The corn silage and alfalfabaseddiets contained 20.0% forage neutral detergentfiber (NDF), 28.5% starch, and 17.1% crude protein.Treatment periods were 21 d with the final 5 d used fordata and sample collection. Treatment did not affectdry matter intake (DMI), milk yield, energy-correctedmilk (ECM), body weight, or body weight change. ThePA+OA diet increased total, 16-carbon, and 18-carbonFA digestibility compared with the PA diet. Comparedwith PA+OA, PA increased fat yield (1.97 vs. 1.91kg/d) and protein yield (1.61 vs. 1.55 kg/d). The PAdiet also increased the yield of de novo (448 vs. 428 g/d)and mixed (749 vs. 669 g/d) milk FA and decreased theyield of preformed FA (605 vs. 627 g/d) compared withPA+OA. Interactions were detected between treatmentand preliminary milk yield for DMI, total FA intake,16-carbon FA intake, ECM, 3.5% fat-corrected milk(linear interaction), and a tendency for milk yield(linear interaction); lower-producing cows (＜45 kg/d)had increased DMI and ECM on the PA diet, whereashigher-producing cows (＞55 kg/d) had increased DMIand ECM on the PA+OA diet. A linear interactionwas detected between treatment and preliminary milkyield for mixed milk FA yield (linear interaction) and atendency for de novo milk FA yield (linear interaction).Our results demonstrate that feeding a fat supplementcontaining more cis-9 C18:1 replacing C16:0 increasedproduction responses (DMI, milk yield, and ECM) inhigher-producing cows, but decreased production responsesin lower-producing cows.