Kristensen N B, Sehested J, Jensen S K, Vestergaard M
Department of Animal Health, Welfare and Nutrition, Faculty of Agricultural Sciences, University of Aarhus, DK-8830 Tjele, Denmark.
J Dairy Sci. 2007 Sep;90(9):4346-55. doi: 10.3168/jds.2006-885.
The aim of the present experiment was to test the hypothesis that a barley-based concentrate would induce an acidic ruminal environment in young calves and that increased milk allowance would alleviate this condition. Eight Holstein calves ruminally cannulated at d 7 +/- 1 of age were used to study the effect of variation in barley-based starter concentrate intake induced by 4 different milk allowances (3.10, 4.84, 6.60, and 8.34 kg of milk replacer/d; 123 g of dry matter/kg of milk) on the ruminal environment, blood variables, and fore-stomach development from wk 2 to 5 of age. Twelve ruminal fluid samples were collected during a weekly 24-h sampling in 4 consecutive weeks. Blood samples were collected by venipuncture between 1200 and 1300 h on ruminal sampling days. Rumen papillae development and visceral organ mass were recorded at slaughter. A linear treatment x week effect was observed for concentrate intake, with the calves fed the lowest milk allowance having the fastest increase in concentrate intake whereby these calves reached the same ME intake in wk 5 compared with calves with the highest milk allowance. Effects on ruminal variables were dominated by week of sampling, with minor differences among treatments. Ruminal pH was below 5.5 for 5 to 13 h/d and all calves with concentrate intake above 20 g of dry matter/d were observed to have a daily ruminal pH minimum at pH 5.5 or lower. The ruminal concentration of total volatile fatty acids (VFA) increased from 71 to 133 +/- 9 mmol/L in wk 2 to 5 and was characterized by a relatively high molar proportion of propionate, increasing from 34 to 40 mol/100 mol of VFA in wk 2 to 5. In addition, the presence of ethanol and propanol as well as numerous VFA esters points to a ruminal environment with a relatively high hydrogen pressure. Plasma glucose and insulin responded to the highest milk allowance in wk 2 to 4. Plasma VFA and ketone bodies increased with the lowest milk allowance in wk 4 to 5. At slaughter, empty wet weights of the rumen + reticulum and omasum as well as mass of digesta in these compartments were found to decrease linearly and perirenal fat was found to increase linearly with milk allowance, indicating that the milk allowance changed the body composition of the calves. Lengths of ruminal papillae in the atrium and ventral ruminal sac were not affected by treatment. We concluded that the ruminal environment of young calves fed a barley-based starter concentrate was characterized by a low ruminal pH and high VFA concentration regardless of the milk allowance.
以大麦为基础的精饲料会在犊牛幼崽中诱导酸性瘤胃环境，而增加牛奶供应量会缓解这种状况。选用8头在7±1日龄时安装了瘤胃瘘管的荷斯坦犊牛，研究4种不同牛奶供应量（3.10、4.84、6.60和8.34千克代乳粉/天；123克干物质/千克牛奶）引起的基于大麦的起始精饲料摄入量变化，对2至5周龄犊牛瘤胃环境、血液指标和前胃发育的影响。在连续4周内，每周进行一次24小时采样，期间采集12份瘤胃液样本。在瘤胃采样日的12:00至13:00之间通过静脉穿刺采集血样。在屠宰时记录瘤胃乳头发育情况和内脏器官质量。观察到精饲料摄入量存在线性处理×周效应，即牛奶供应量最低的犊牛精饲料摄入量增加最快，到第5周时，这些犊牛与牛奶供应量最高的犊牛达到相同的代谢能摄入量。对瘤胃变量的影响主要受采样周数的影响，各处理之间差异较小。瘤胃pH值每天有5至13小时低于5.5，所有精饲料摄入量超过20克干物质/天的犊牛，其瘤胃pH值每日最低值均在5.5或更低。瘤胃中总挥发性脂肪酸（VFA）浓度在第2至5周从71增加到133±9毫摩尔/升，其特点是丙酸的摩尔比例相对较高，从第2至5周的34摩尔/100摩尔VFA增加到40摩尔/100摩尔VFA。此外，乙醇、丙醇以及多种VFA酯的存在表明瘤胃环境具有相对较高的氢气压力。血浆葡萄糖和胰岛素在第2至4周对最高牛奶供应量有反应。血浆VFA和酮体在第4至5周随着最低牛奶供应量而增加。在屠宰时，发现瘤胃+网胃和瓣胃的空湿重以及这些腔室中的食糜质量随牛奶供应量呈线性下降，而肾周脂肪随牛奶供应量呈线性增加，这表明牛奶供应量改变了犊牛的身体组成。瘤胃心房和瘤胃腹囊的瘤胃乳头长度不受处理影响。我们得出结论，无论牛奶供应量如何，以大麦为基础的起始精饲料喂养的犊牛瘤胃环境的特点是瘤胃pH值低和VFA浓度高。
