Litherland N B, Thire S, Beaulieu A D, Reynolds C K, Benson J A, Drackley J K
Department of Animal Sciences, University of Illinois, Urbana 61801, USA.
J Dairy Sci. 2005 Feb;88(2):632-43. doi: 10.3168/jds.S0022-0302(05)72727-2.
Previous experiments from our group have demonstrated that abomasal infusion of unsaturated free fatty acids (FFA) markedly decreases dry matter intake (DMI) in dairy cows. In contrast, experiments from other groups have noted smaller decreases in DMI when unsaturated triglycerides (TG) were infused postruminally. Our hypothesis was that unsaturated FFA would be more potent inhibitors of DMI than an equivalent amount of unsaturated TG. Four Holstein cows in late lactation were used in a single reversal design. Cows were fed a total mixed ration containing (DM basis) 23% alfalfa silage, 23% corn silage, 40.3% ground shelled corn, and 10.5% soybean meal. Two cows received soy FFA (UFA; 0, 200, 400, 600 g/d) and 2 received soy oil (TG) in the same amounts; cows then were switched to the other lipid source. Cows were abomasally infused with each amount for 5-d periods. The daily amount of lipid was pulse-dosed in 4 equal portions at 0600, 1000, 1700, and 2200 h; no emulsifiers were used and there was no sign of digestive disturbance. Both lipid sources linearly decreased DMI, with a significant interaction between lipid source and amount. Slope-ratio analysis indicated that UFA were about 2 times more potent in decreasing DMI than were TG. Decreased DMI led to decreased milk production. Milk fat content was increased linearly by lipid infusion. Milk fat yield decreased markedly for UFA infusion but was relatively unaffected by infusion of TG. Contents of short- and medium-chain fatty acids in milk fat decreased as the amount of either infusate increased. Contents of C(18:2) and C(18:3) in milk fat were increased linearly by abomasal infusion of either fat source; cis-9 C(18:1) was unaffected. Transfer of infused C(18:2) to milk fat was 35.6, 42.5, and 27.8% for 200, 400, and 600 g/d of UFA, and 34.3, 39.6, and 34.0% for respective amounts of TG. Glucagon-like peptide-1 (7-36) amide (GLP-1) concentration in plasma significantly increased as DMI decreased with increasing infusion amount of UFA or TG. Plasma concentration of cholecystokinin-octapeptide (CCK-8) was unaffected by lipid infusion. These results indicate that unsaturated FFA reaching the duodenum are more potent inhibitors of DMI than are unsaturated TG; the effect may be at least partially mediated by GLP-1.
我们团队之前的实验表明，向皱胃灌注不饱和游离脂肪酸（FFA）会显著降低奶牛的干物质摄入量（DMI）。相比之下，其他团队的实验指出，当在瘤胃后灌注不饱和甘油三酯（TG）时，DMI的降低幅度较小。我们的假设是，不饱和FFA对DMI的抑制作用比等量的不饱和TG更强。选用4头处于泌乳后期的荷斯坦奶牛进行单反转设计实验。给奶牛饲喂一种全混合日粮（以干物质计），其中包含23%的苜蓿青贮、23%的玉米青贮、40.3%的去壳玉米粉和10.5%的豆粕。2头奶牛接受大豆FFA（UFA；0、200、400、600 g/天），另外2头奶牛接受等量的大豆油（TG）；之后奶牛更换为另一种脂质来源。每种剂量的脂质均以5天为周期向皱胃灌注。每日脂质剂量在0600、1000、1700和2200时以4等份脉冲给药；未使用乳化剂，且没有消化紊乱的迹象。两种脂质来源均使DMI呈线性下降，脂质来源与剂量之间存在显著交互作用。斜率比分析表明，UFA降低DMI的效力约为TG的2倍。DMI降低导致产奶量下降。脂质灌注使乳脂含量呈线性增加。UFA灌注使乳脂产量显著下降，但TG灌注对其影响相对较小。随着两种灌注物剂量的增加，乳脂中短链和中链脂肪酸的含量降低。向皱胃灌注任何一种脂肪来源均使乳脂中C（18:2）和C（18:3）的含量呈线性增加；顺式-9 C（18:1）不受影响。对于200、400和600 g/天的UFA，灌注的C（18:2）向乳脂的转移率分别为35.6%、42.5%和27.8%，对于相应剂量的TG，转移率分别为34.3%、39.6%和34.0%。随着UFA或TG灌注量增加导致DMI下降，血浆中胰高血糖素样肽-1（7-36）酰胺（GLP-1）浓度显著升高。脂质灌注对血浆中八肽胆囊收缩素（CCK-8）浓度无影响。这些结果表明，到达十二指肠的不饱和FFA对DMI的抑制作用比不饱和TG更强；这种作用可能至少部分由GLP-1介导。
