Animal Nutrition Group, Department of Animal Sciences, Wageningen University, PO Box 338, 6700 AH Wageningen, the Netherlands.
J Dairy Sci. 2012 Mar;95(3):1472-83. doi: 10.3168/jds.2011-4701.
The variation in maturity at harvest during grain filling has a major effect on the carbohydrate composition (starch:NDF ratio) and fatty acid (FA) content of corn silages, and can alter the FA composition of milk fat in dairy cows. This study evaluated the effect of silage corn (cv. Atrium) harvested and ensiled at targeted DM contents of 300, 340, 380, and 420 g/kg of fresh weight and fed to dairy cows in combination with a highly degradable carbohydrate (HC) or low-degradable carbohydrate concentrate, on the nutrient intake, milk yield, and composition of milk and milk fat. Sixty-four multiparous Holstein-Friesian dairy cows in their first week of lactation were assigned to the 8 dietary treatments according to a randomized complete block design. The 8 dietary treatments consisted of a factorial combination of the 4 corn silages and the 2 concentrates. Corn silages were offered ad libitum as part of a basal forage mixture, whereas the concentrates were given at the rate of 8.5 kg of DM/cow per day during the 15-wk experimental period. Dry matter, crude protein, and energy intakes did not differ across the corn silages. However, the intake of starch increased, and those of NDF and C18:3n-3 decreased with increasing maturation. Milk yield and composition were not different across the corn silages. Yield (kg/d) of milk, protein, and lactose was higher for low-degradable carbohydrate compared with HC concentrate-fed groups. Increasing maturity of corn silages decreased the content of C18:3n-3 and total n-3 and increased the n-6:n-3 ratio in milk fat. Concentrate type significantly altered the composition of all trans FA, except C18:2 trans-9,12. Inclusion of the HC concentrate in the diets increased the contents of all C18:1 trans isomers, C18:2 cis-9,trans-11, and C18:2 trans-10,cis-12 conjugated linoleic acid in milk fat. Milk fat composition was strongly influenced by the stage of lactation (wk 3 to 10). The content of all even short- and medium-chain FA changed with lactation, except C8:0 and C10:0. The content of C12:0, C14:0, and C16:0 and total saturated FA increased and the content of C18:0, C18:1 cis total, and total cis monounsaturated FA decreased with lactation. Maturity of the corn silages at harvest did not affect the production performance of dairy cows, but resulted in a decreased content of C18:3n-3, total n-3, and an increased n-6:n-3 ratio in the milk fat of dairy cows.
在谷物灌浆期间收获时的成熟度变化对玉米青贮饲料的碳水化合物组成（淀粉：NDF 比）和脂肪酸（FA）含量有重大影响，并可以改变奶牛乳脂中的 FA 组成。本研究评估了青贮玉米（cv. Atrium）在目标 DM 含量为 300、340、380 和 420 g/kg 鲜重下收获和青贮，并与高可降解碳水化合物（HC）或低可降解碳水化合物浓缩物组合，对奶牛的营养摄入、产奶量以及牛奶和乳脂的组成的影响。64 头处于泌乳第一周的荷斯坦-弗里生奶牛根据随机完全区组设计分配到 8 种日粮处理中。8 种日粮处理是由 4 种玉米青贮和 2 种浓缩物的因子组合而成。玉米青贮作为基础饲草混合物的一部分自由采食，而浓缩物在 15 周实验期间每天以 8.5kgDM/奶牛的速度给予。在玉米青贮中，干物质、粗蛋白和能量的摄入量没有差异。然而，随着成熟度的增加，淀粉的摄入量增加，NDF 和 C18:3n-3 的摄入量减少。玉米青贮对牛奶产量和组成没有影响。低可降解碳水化合物组的产奶量（kg/d）、蛋白和乳糖较高。玉米青贮成熟度的增加降低了乳脂中 C18:3n-3 和总 n-3 的含量，并增加了 n-6:n-3 比值。浓缩物类型显著改变了所有反式 FA 的组成，除了 C18:2 trans-9,12。在日粮中添加 HC 浓缩物增加了乳脂中所有 C18:1 反式异构体、C18:2 cis-9,trans-11 和 C18:2 trans-10,cis-12 共轭亚油酸的含量。乳脂组成受泌乳阶段（第 3 周到第 10 周）的强烈影响。所有偶数短链和中链 FA 的含量都随着泌乳而变化，除了 C8:0 和 C10:0。C12:0、C14:0 和 C16:0 的含量以及总饱和 FA 增加，C18:0、C18:1 cis 总量和总顺式单不饱和 FA 减少。玉米青贮在收获时的成熟度并不影响奶牛的生产性能，但导致奶牛乳脂中的 C18:3n-3、总 n-3 和 n-6:n-3 比值降低。
