Jurjanz S, Monteils V, Juaneda P, Laurent F
Laboratoire de Sciences Animales, Institut National de la Recherche Agronomique-Ecole Nationale Supérieure d'Agronomique et des Industries Alimentaires (INRA-ENSAIA), Vandoeuvre-lès-Nancy, France.
Lipids. 2004 Jan;39(1):19-24. doi: 10.1007/s11745-004-1196-4.
The impact of starch sources differing in their velocities of ruminal degradation on the milk fat of dairy cows was studied. The animals received diets containing a slowly degradable (potatoes) or rapidly degradable (wheat) starch concentrate (40% of the dry matter) in a total mixed diet. Milk fat was the only animal performance factor affected: Cows produced significantly less milk fat when fed the wheat diet than the potato diet (-3.3 g/kg, -122 g/d; P < 0.05). With the wheat diet, milk fat was poorer in short-chain FA and richer in unsaturated long-chain FA, especially in trans octadecenoic acid (4.4 vs. 2.7% of the total FA, P < 0.05). A very large increase in the isomer trans-10 18:1 (+1.46% of the total FA) was observed. Because no difference in volatile FA concentrations in the rumen was revealed, the increase in trans octadecenoic acids, and particularly the isomer trans-10 18:1, was associated with the larger postprandial drop in ruminal pH with wheat. Similar concentrate levels and FA profiles in both diets indicated that the decrease in milk fat was due to changes in the ruminal environment. Quicker degradation of wheat starch, and hence a greater drop in pH with this diet associated with the absence of any effect on volatile FA, strengthen the hypothesis developed in the literature of enzyme inhibition via increased levels of trans octadecenoic acids, especially the trans-10 isomer. Hence, milk fat can be decreased with rapidly degradable starch sources and not only with high levels of concentrates in the diet or added fat. More detailed work is necessary to elucidate the microorganisms involved and to determine whether metabolic pathways similar to those reported for high-concentrate diets are involved.
研究了瘤胃降解速度不同的淀粉来源对奶牛乳脂的影响。动物采食的全混合日粮中含有缓慢降解（土豆）或快速降解（小麦）的淀粉浓缩物（占干物质的40%）。乳脂是唯一受影响的动物生产性能指标：饲喂小麦日粮的奶牛产奶脂量显著低于饲喂土豆日粮的奶牛（-3.3 g/kg，-122 g/d；P<0.05）。采食小麦日粮时，乳脂中的短链脂肪酸含量较低，不饱和长链脂肪酸含量较高，尤其是反式十八碳烯酸（占总脂肪酸的4.4%对2.7%，P<0.05）。观察到反式-10 18:1异构体大幅增加（占总脂肪酸的+1.46%）。由于瘤胃中挥发性脂肪酸浓度没有差异，反式十八碳烯酸增加，尤其是反式-10 18:1异构体增加，与采食小麦后瘤胃pH值餐后下降幅度较大有关。两种日粮中相似的浓缩物水平和脂肪酸谱表明，乳脂下降是由于瘤胃环境的变化。小麦淀粉降解更快，因此采食该日粮时pH值下降幅度更大，且对挥发性脂肪酸没有任何影响，这强化了文献中提出的通过增加反式十八碳烯酸水平，尤其是反式-10异构体水平来抑制酶活性的假说。因此，快速降解的淀粉来源会降低乳脂，而不仅仅是日粮中高含量的浓缩物或添加脂肪会导致乳脂降低。需要更详细的研究来阐明其中涉及的微生物，并确定是否涉及与高浓缩日粮报道的类似代谢途径。
