Department of Dairy Science, University of Wisconsin, Madison, WI 53706, USA.
J Anim Sci. 2013 May;91(5):2243-53. doi: 10.2527/jas.2012-5169. Epub 2013 Mar 5.
The objectives of this study were 1) to determine the level of lauric acid (LA) addition to the diet necessary to effectively suppress ruminal protozoa (RP) to the extent observed when a single dose was given directly into the rumen, 2) to assess LA effects on production and ruminal metabolism, and 3) to determine the time needed for RP to reestablish themselves after LA is withdrawn from the diet of lactating dairy cows. In Exp. 1, 2 Holstein cows fitted with ruminal cannulae were used in a split-plot design pilot study. Both cows consumed the same level of LA, starting with 0 g/d and increasing to 129, 270, and 438 g/d mixed into the diet. Diets were fed as total mixed ration (TMR) and contained (DM basis) 30% corn silage, 30% alfalfa silage, and 40% concentrate. Lauric acid intake linearly decreased DMI (P = 0.03), RP numbers (P < 0.01), ruminal acetate molar proportion (P = 0.03), and ruminal ammonia concentration (P = 0.03). Lauric acid intake linearly increased ruminal valerate molar proportion (P = 0.02). A quadratic response of LA consumption was observed on total ruminal VFA concentration (P < 0.01) and propionate molar proportion (P < 0.01), with maximum responses at 270 g/d of LA intake. A quadratic response of LA consumption was also observed on total ruminal free amino acid (TAA) concentration (P < 0.01), with minimum concentration at 270 g/d of LA intake. After withdrawing the greatest LA dose from the diet, RP returned to their original numbers in 12 d. In Exp. 2, 48 multiparous Holstein cows (8 with ruminal cannulae) were blocked by days in milk into 12 blocks of 4 cows (2 blocks of cannulated cows) and randomly assigned within replicated 4 × 4 Latin squares to balanced dietary treatment sequences. Diets were fed as TMR and contained (DM basis) 36% corn silage, 29% alfalfa silage, and 35% concentrate, and LA intake levels were 0, 220, 404, and 543 g/d mixed in the TMR. In Exp. 2, LA linearly reduced RP (P < 0.01), ruminal ammonia (P < 0.01), and total free AA concentration (P < 0.01); however, dietary LA also linearly decreased DM intake (P < 0.01). Intake of LA linearly reduced ruminal total VFA concentration (P < 0.01); DM, OM, NDF, and CP digestibility (P < 0.01); and milk production and milk components (P < 0.01). Therefore, LA does not appear to be a feasible RP suppressant for feeding in practical diets.
1）确定饮食中添加月桂酸（LA）的水平，以有效抑制反刍动物瘤胃原虫（RP），使其达到单次直接向瘤胃内添加时观察到的水平；2）评估 LA 对生产和瘤胃代谢的影响；3）确定在泌乳奶牛日粮中去除 LA 后 RP 重新建立所需的时间。在实验 1 中，2 头安装瘤胃瘘管的荷斯坦奶牛采用裂区设计进行了初步研究。这 2 头奶牛均以 0 g/d 的起始水平摄入 LA，然后逐渐增加至 129、270 和 438 g/d 混合在日粮中。日粮作为全混合日粮（TMR），含有（DM 基础）30%玉米青贮、30%苜蓿青贮和 40%精料。LA 摄入量线性降低了干物质采食量（P = 0.03）、RP 数量（P < 0.01）、瘤胃乙酸摩尔比例（P = 0.03）和瘤胃氨浓度（P = 0.03）。LA 摄入量线性增加了瘤胃戊酸摩尔比例（P = 0.02）。LA 消耗的二次反应观察到总瘤胃 VFA 浓度（P < 0.01）和丙酸摩尔比例（P < 0.01），LA 摄入量最大的响应在 270 g/d。LA 消耗的二次反应也观察到总瘤胃游离氨基酸（TAA）浓度（P < 0.01），LA 摄入量最低时为 270 g/d。从日粮中去除最大剂量的 LA 后，RP 在 12 天内恢复到原来的数量。在实验 2 中，48 头经产荷斯坦奶牛（8 头带有瘤胃瘘管）根据泌乳天数分为 12 个 4 头的块（2 个带有瘤胃瘘管的块），并在重复的 4 × 4 拉丁方内随机分配到平衡的日粮处理序列中。日粮作为 TMR，含有（DM 基础）36%玉米青贮、29%苜蓿青贮和 35%精料，LA 摄入量分别为 0、220、404 和 543 g/d 混合在 TMR 中。在实验 2 中，LA 线性降低 RP（P < 0.01）、瘤胃氨（P < 0.01）和总游离 AA 浓度（P < 0.01）；然而，日粮中的 LA 也线性降低了干物质采食量（P < 0.01）。LA 的摄入线性降低了瘤胃总 VFA 浓度（P < 0.01）；DM、OM、NDF 和 CP 消化率（P < 0.01）；和牛奶产量和牛奶成分（P < 0.01）。因此，LA 似乎不是一种可行的 RP 抑制剂，不能在实际日粮中添加。
