我们研究的目的是评估改变饮食中醋酸盐供应的效果,棕榈酸(PA),和棉籽对泌乳奶牛的乳成分和乳脂肪酸(FA)产量的影响。32头多胎荷斯坦奶牛(牛奶中133±57d,50.5±7.2kg/d牛奶)用于4×4拉丁方分割地块设计,并采用2×2阶乘排列的子地块处理。母牛被能量校正的牛奶(ECM)产量所阻断,并被分配到接受基础饮食(n=16)的主要地块,没有补充PA(低PA)或基础饮食(n=16),其中1.5%包含含有约85%PA(高PA)的FA补充剂。在每个主要情节中,以下处理饮食的子图以由14天周期组成的拉丁方排列喂养:1)对照饮食(CON),2)对照日粮补充3%乙酸钠(AC),3)对照日粮补充12%全棉籽(CS),和4)补充有3%乙酸钠和12%全棉籽(CS+AC)的对照日粮。PA补充剂和乙酸钠取代了大豆壳,整个棉籽代替了棉籽壳和粗粉。所有饮食都平衡了30%的中性洗涤剂纤维(NDF),23%饲草NDF,28%淀粉,和17%粗蛋白(CP)。FA的来源被分类为从头(<16个碳),混合(16碳),并预制(>16个碳)。统计模型包括基础日粮内母牛嵌套的随机效应和周期的固定效应,基础饮食,醋酸盐,棉籽,和他们的互动。基础饮食之间的三向相互作用,醋酸盐,观察到棉籽的乳脂产量,3.5%脂肪校正牛奶(FCM),和从头FA的摩尔产率,混合FA,和预制FA。在低PA饮食中,与CON和CS相比,AC和CSAC增加了乳脂和FCM的产量,然而,在高PA饮食中,与其他处理相比,CSAC增加了乳脂和FCM的产量,而与CON和CS相比,AC增加了乳脂的产量。与低PA相比,高PA增加乳脂含量,混合FA产量,并有提高C4:0产量的趋势。含有醋酸盐的饮食增加了dmi和乳脂的产量,ECM,FCM,从头FA,混合FA,和预制FA与不含乙酸盐的饮食相比。含有棉籽的饮食增加了牛奶和预制FA的产量,倾向于增加FCM和蛋白质的产量,与不含棉籽的日粮相比,DMI和从头FA和混合FA的产量降低。总之,在高PA饮食中,与其他处理相比,乙酸盐和棉籽的加入增加了乳脂产量。高PA中的CON饮食增加乳脂肪产量的程度与低PA中的AC和CSAC相同,表明PA对于启动乳TG合成很重要。平衡从头FA底物和预先形成的FA的供应对于增加乳脂甘油三酯的合成和乳脂产量是重要的。
The objective of our study was to evaluate the effect of altering the dietary supply of acetate, palmitic acid (PA), and cottonseed on the yields of milk components and milk fatty acids (FA) in lactating dairy cows. Thirty-two multiparous Holstein cows (133 ± 57 d in milk, 50.5 ± 7.2 kg/d milk) were used in a 4 × 4 Latin square split plot design with a 2 × 2 factorial arrangement of subplot treatments. Cows were blocked by energy-corrected milk (ECM) yield and allocated to a main plot receiving a basal diet (n = 16) with no supplemental PA (Low PA) or a basal diet (n = 16) with 1.5% inclusion of a FA supplement containing ~85% PA (High PA). In each main plot, the following subplots of treatment diets were fed in a Latin square arrangement consisting of 14-d periods: 1) a control diet (CON), 2) the control diet supplemented with 3% sodium acetate (AC), 3) the control diet supplemented with 12% whole cottonseed (CS), and 4) the control diet supplemented with 3% sodium acetate and 12% whole cottonseed (CS+AC). The PA supplement and sodium acetate replaced soyhulls, and whole cottonseed replaced cottonseed hulls and meal. All diets were balanced for 30% neutral detergent fiber (NDF), 23% forage NDF, 28% starch, and 17% crude protein (CP). Sources of FA were classified as de novo (<16 carbons), mixed (16-carbon), and preformed (>16 carbons). The statistical model included the random effect of cow nested within basal diet and fixed effect of period, basal diet, acetate, cottonseed, and their interactions. Three-way interactions among basal diet, acetate, and cottonseed were observed for the yields of milk fat, 3.5% fat-corrected milk (FCM), and the molar yields of de novo FA, mixed FA, and preformed FA. In the Low PA diets, AC and CS+AC increased the yields of milk fat and FCM compared with CON and CS, whereas, in the High PA diets, CS+AC increased the yields of milk fat and FCM compared with the other treatments and AC increased milk fat yield compared with CON and CS. Compared with Low PA, High PA increased milk fat content, mixed FA yield, and tended to increase C4:0 yield. Diets containing acetate increased DMI and the yields of milk fat, ECM, FCM, de novo FA, mixed FA, and preformed FA compared with diets without acetate. Diets containing cottonseed increased the yields of milk and preformed FA, tended to increase the yields of FCM and protein, and decreased DMI and the yields of de novo FA and mixed FA compared with diets without cottonseed. In summary, in high PA diets, the inclusion of acetate plus cottonseed increased milk fat yield compared with the other treatments. The CON diet in High PA increased milk fat yield to the same extent as AC and CS+AC in Low PA suggesting PA is important for initiating milk TG synthesis. Balancing the supply of de novo FA substrates and preformed FA is important for increasing the synthesis of milk fat triglycerides and milk fat production.