Effect of pH and level of concentrate in the diet on the production of biohydrogenation intermediates in a dual-flow continuous culture.
Effect of pH and level of concentrate in the diet on the production of biohydrogenation intermediates in a dual-flow continuous culture.
复制标题
DOI：
10.3168/jds.2008-1722
复制
发表时间：
2009-09
影响因子：
3.5
通讯作者：
MC Fuentes;S. Calsamiglia;P. Cardozo;B. Vlaeminck
中科院分区：
文献类型：
--
作者：
MC Fuentes;S. Calsamiglia;P. Cardozo;B. Vlaeminck
饲喂高谷物饲料的奶牛乳脂下降与牛奶中反式-10C(18：1)和反式-10，顺式-12共轭亚油酸(CLA)浓度增加有关。这些脂肪酸(FA)是由于日粮不饱和脂肪酸的瘤胃生物氢化改变而产生的。由于在饲喂高精料时通常会观察到瘤胃pH的降低，因此决定生物氢化途径变化的主要原因尚不清楚。通过连续培养试验，研究了pH值(6.4vs.5.6)和饲料精料比(F：C；70：30F：C和30：70F：C)对瘤胃微生物发酵、出水FA谱和参与脂肪分解和生物氢化过程的细菌DNA浓度的影响。双流连续培养包括2个周期，8d(适应5d，采样3d)，处理采用2×2因子安排。从固体和液体混合流出物中采集样品，用于总氮、氨氮和挥发性脂肪酸浓度的测定，其余样品进行冷冻干燥。干样分析了干物质、灰分、中性和酸性洗涤纤维、FA和嘌呤含量。PH 5.6降低了有机物和纤维的消化率，降低了氨氮浓度和流量，降低了粗蛋白降解率，增加了非氨氮和饲料氮流量。在进料后1h内，pH 5.6降低了C(18：0)、反式-11C(18：1)和顺-9、反式-11CLA的流量，增加了反式-10C(18：1)、C(18：2n-6)、C(18：3n-3)、反式-11、顺-15C(18：2)和反式-10、顺-12CLA的流量。PH 5.6降低了解脂厌氧弧菌(32.7 pg/10 ng总DNA)和纤维分离丁状弧菌疫苗酸亚组(588 pg/10 ng总DNA)的DNA浓度。高精料增加了有机物和纤维的消化率、非氨氮和细菌氮的流动，降低了氨氮的浓度和流动。高精料降低了投喂后1h的反式-11C(18：1)和反式-10C(18：1)，增加了C(18：2n-6)、C(18：3n-3)和反式-10、顺-12CLA的比例。在高精料条件下，饲料中反式-10、顺式-12共轭亚油酸的比例在投喂后1h内的增加幅度小于pH值为5.6时的水平。结果表明，pH是导致反式-10C(18：1)和反式-10、顺-12CLA在出水中积累的主要原因，但饲料中高浓度的精料也会影响反式-10、顺-12CLA的比例。
Milk fat depression in cows fed high-grain diets has been related to an increase in the concentration of trans-10 C(18:1) and trans-10,cis-12 conjugated linoleic acid (CLA) in milk. These fatty acids (FA) are produced as a result of the alteration in rumen biohydrogenation of dietary unsaturated FA. Because a reduction in ruminal pH is usually observed when high-concentrate diets are fed, the main cause that determines the alteration in the biohydrogenation pathways is not clear. The effect of pH (6.4 vs. 5.6) and dietary forage to concentrate ratios (F:C; 70:30 F:C vs. 30:70 F:C) on rumen microbial fermentation, effluent FA profile, and DNA concentration of bacteria involved in lipolysis and biohydrogenation processes were investigated in a continuous culture trial. The dual-flow continuous culture consisted of 2 periods of 8 d (5 d for adaptation and 3 d for sampling), with a 2 x 2 factorial arrangement of treatments. Samples from solid and liquid mixed effluents were taken for determination of total N, ammonia-N, and volatile fatty acid concentrations, and the remainder of the sample was lyophilized. Dry samples were analyzed for dry matter, ash, neutral and acid detergent fiber, FA, and purine contents. The pH 5.6 reduced organic matter and fiber digestibility, ammonia-N concentration and flow, and crude protein degradation, and increased nonammonia and dietary N flows. The pH 5.6 decreased the flow of C(18:0), trans-11 C(18:1) and cis-9, trans-11 CLA, and increased the flow of trans-10 C(18:1), C(18:2n-6), C(18:3n-3), trans-11,cis-15 C(18:2) and trans-10,cis-12 CLA in the 1 h after feeding effluent. The pH 5.6 reduced Anaerovibrio lipolytica (32.7 vs. 72.1 pg/10 ng of total DNA) and Butyrivibrio fibrisolvens vaccenic acid subgroup (588 vs. 1,394 pg/10 ng of total DNA) DNA concentrations. The high-concentrate diet increased organic matter and fiber digestibility, nonammonia and bacterial N flows, and reduced ammonia-N concentration and flow. The high-concentrate diet reduced trans-11 C(18:1) and trans-10 C(18:1), and increased C(18:2n-6), C(18:3n-3) and trans-10,cis-12 CLA proportions in the 1 h after feeding effluent. The increase observed in trans-10,cis-12 CLA proportion in the 1 h after feeding effluent due to the high-concentrate diet was smaller that that observed at pH 5.6. Results indicate that the pH is the main cause of the accumulation of trans-10 C(18:1) and trans-10, cis-12 CLA in the effluent, but the trans-10,cis-12 CLA proportion can be also affected by high levels of concentrate in the diet.