Farmer C G, Cochran R C, Nagaraja T G, Titgemeyer E C, Johnson D E, Wickersham T A
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66505, USA.
J Anim Sci. 2004 Mar;82(3):895-903. doi: 10.2527/2004.823895x.
The effect of altering supplementation frequency on host N balance and key N transactions in the ruminal ecosystem were monitored. Four ruminally fistulated beef steers (BW = 513 kg; SEM = 6.5) were used in a 2 x 2 crossover design with two periods and two supplementation frequency treatments. Supplementation frequencies were 2 and 7 d/wk. Steers were fed tallgrass prairie hay (73.1% NDF, 5.3% CP) ad libitum. Supplement (42% CP; DM basis) was fed at 0.36% BW/d to steers supplemented 7 d/wk. Steers supplemented 2 d/wk received the same amount of supplement per week, but it was equally split among the two supplementation events. Steers supplemented 7 d/wk had higher forage (P < 0.02) and total digestible OM intake (P < 0.06), total N intake, fecal N excretion, and N retention. Although both supplementation frequencies were characterized by positive N balance, the decrease in N retention in the steers supplemented 2 d/wk was due to higher (P < 0.01) urinary N loss. Ruminal fluid was sampled at 0, 2, 4, 6, 12, 24, 48, and 72 h after supplementation beginning on a day when both treatments were supplemented. Frequency x hour interactions (P < 0.02) were observed for ruminal N metabolism criteria. Counts of peptide- and AA-fermenting bacteria peaked at 2 h and returned to nadir by 12 h for steers supplemented 7 d/wk. Steers supplemented 2 d/wk peaked at 6 h with a greater population and returned to nadir at 48 h. Ruminal ammonia concentrations followed a similar trend. Specific activity of ammonia production was lower (P < or = 0.05) immediately after supplementation for steers supplemented 2 d/wk, but by 12 h was the same as for 7 d/wk steers. Ruminal peptides and free AA peaked at 2 h for steers supplemented 2 d/wk and were generally higher (P < or = 0.05) during the first 6 h compared with steers supplemented 7 d/wk. Total VFA concentration was not different (P = 0.35) due to supplementation frequency. Frequency x hour interactions (P < 0.01) were observed for all molar proportions of VFA. The molar proportion of acetate and acetate:propionate ratio were lower (P < 0.01) and the molar proportions of propionate and butyrate were higher for steers supplemented 2 d/wk from 4 h to 24 h. In conclusion, forage use and N balance improved with supplementation 7 d/wk, but supplementation 2 d/wk was associated with some desirable shifts in select ruminal events that may contribute to moderating potential negative impacts of supplementing infrequently.
监测了改变补饲频率对宿主氮平衡及瘤胃生态系统中关键氮代谢的影响。选用4头瘤胃造瘘的肉牛（体重=513千克；标准误=6.5），采用2×2交叉设计，分为两个阶段和两种补饲频率处理。补饲频率分别为每周2次和每周7次。肉牛自由采食高草草原干草（中性洗涤纤维含量73.1%，粗蛋白含量5.3%）。每周补饲7次的肉牛，补饲量为体重的0.36%/天（以42%粗蛋白、干物质计）。每周补饲2次的肉牛每周补饲量相同，但分两次等量补饲。每周补饲7次的肉牛，其牧草采食量（P<0.02）、总可消化有机物摄入量（P<0.06）、总氮摄入量、粪便氮排泄量和氮保留量均较高。虽然两种补饲频率下氮平衡均为正值，但每周补饲2次的肉牛氮保留量降低是由于尿氮损失较高（P<0.01）。在两种处理都进行补饲的一天，补饲开始后0、2、4、6、12、24、48和72小时采集瘤胃液。观察到瘤胃氮代谢指标存在频率×小时交互作用（P<0.02）。对于每周补饲7次的肉牛，肽和氨基酸发酵细菌数量在2小时达到峰值，12小时降至最低点。每周补饲2次的肉牛在6小时达到峰值，数量更多，48小时降至最低点。瘤胃氨浓度呈现类似趋势。每周补饲2次的肉牛补饲后立即氨产生的比活性较低（P≤0.05），但到12小时与每周补饲7次的肉牛相同。每周补饲2次的肉牛瘤胃肽和游离氨基酸在2小时达到峰值，在前6小时总体上高于（P≤0.05）每周补饲7次的肉牛。补饲频率对总挥发性脂肪酸浓度无显著影响（P=0.35）。观察到挥发性脂肪酸所有摩尔比例均存在频率×小时交互作用（P<0.01）。从4小时到24小时，每周补饲2次的肉牛乙酸摩尔比例和乙酸:丙酸比值较低（P<0.01），丙酸和丁酸摩尔比例较高。总之，每周补饲7次可提高牧草利用率和氮平衡，但每周补饲2次会使某些瘤胃事件发生一些有益变化，这可能有助于减轻不频繁补饲的潜在负面影响。
