Golder H M, Celi P, Rabiee A R, Lean I J
Dairy Science Group, Faculty of Veterinary Science, The University of Sydney, Camden, New South Wales, Australia 2570; SBScibus, Camden, New South Wales, Australia 2570.
Dairy Science Group, Faculty of Veterinary Science, The University of Sydney, Camden, New South Wales, Australia 2570; Melbourne School of Land and Environment, The University of Melbourne, Parkville, Victoria, Australia, 3052.
J Dairy Sci. 2014 Feb;97(2):985-1004. doi: 10.3168/jds.2013-7166. Epub 2013 Nov 7.
We evaluated the effect of feed additives on the risk of ruminal acidosis in Holstein heifers (n = 40) fed starch and fructose in a challenge study. Heifers were randomly allocated to feed additive groups (n = 8 heifers/group): (1) control (no additives); (2) virginiamycin (VM); (3) monensin + tylosin (MT); (4) monensin + live yeast (MLY); and (5) sodium bicarbonate + magnesium oxide (BUF). Heifers were fed 2.5% of body weight (BW) dry matter intake (DMI) per day of a total mixed ration (62:38 forage:concentrate) and feed additives for a 20-d adaptation period. Fructose (0.1% of BW/d) was included for the last 10d of the adaptation period. On d 21, heifers were fed to target a DMI of 1.0% of BW of wheat, fructose at 0.2% of BW, and their feed additives. Rumen fluid samples obtained by stomach tube and blood samples were collected weekly as well as during a 3.6-h period on challenge day (d 21). Virginiamycin and BUF groups maintained a consistently high DMI across the 20-d adaptation period. The MLY heifers had low DMI of the challenge ration. Average daily gain and feed conversion ratio were not affected by feed additives. All rumen and plasma measures changed weekly over adaptation and over the challenge sampling period with the exception of rumen total lactate and histamine concentrations, plasma oxidative stress index, and ceruloplasmin. Substantial within- and between-group variation was observed in rumen and plasma profiles at challenge sampling. No significant group changes were observed in rumen total volatile fatty acids, propionate, acetate-to-propionate ratio, isobutyrate, caproate, isovalerate, total lactate, d- and l-lactate, and pH measures on challenge day. Acetate concentration was increased in the BUF and control groups on challenge day. Butyrate concentration was lower in the MLY and MT groups compared with other groups at challenge. Valerate concentrations were lowest in the control, VM, and BUF groups and lactate concentrations were numerically lower in the MLY, VM, and BUF groups. Total lactate concentrations were >10mM for each group throughout the challenge. Ammonia concentrations were lower in the MLY and MT groups. Histamine concentrations were decreased in MLY and increased in the VM and BUF groups. Plasma oxidative stress measures were not influenced by feed additives weekly or on challenge day, except for an increase in biological antioxidant potential in the control, VM, and MT groups on challenge day. Despite the large within-animal variation, all feed additives modified rumen function and may influence the risk of acidosis by different mechanisms; however, none stabilized the rumen in all heifers.
在一项挑战研究中，我们评估了饲料添加剂对饲喂淀粉和果糖的荷斯坦小母牛（n = 40）瘤胃酸中毒风险的影响。小母牛被随机分配到饲料添加剂组（每组n = 8头小母牛）：（1）对照组（无添加剂）；（2）维吉尼亚霉素（VM）；（3）莫能菌素+泰乐菌素（MT）；（4）莫能菌素+活酵母（MLY）；以及（5）碳酸氢钠+氧化镁（BUF）。小母牛每天按体重（BW）的2.5%摄入全混合日粮（粗饲料：精饲料为62:38）和饲料添加剂，为期20天的适应期。在适应期的最后10天添加果糖（0.1%BW/d）。在第21天，给小母牛饲喂目标采食量为体重1.0%的小麦、0.2%BW的果糖以及它们的饲料添加剂。通过胃管采集瘤胃液样本和血液样本，每周采集一次，在挑战日（第21天）还在3.6小时内采集。在整个20天的适应期内，维吉尼亚霉素组和BUF组的干物质采食量（DMI）一直保持较高水平。MLY组小母牛对挑战日粮的采食量较低。平均日增重和饲料转化率不受饲料添加剂影响。除了瘤胃总乳酸和组胺浓度、血浆氧化应激指数和铜蓝蛋白外，所有瘤胃和血浆指标在适应期和挑战采样期每周都有变化。在挑战采样时，瘤胃和血浆指标在组内和组间均观察到显著差异。在挑战日，瘤胃总挥发性脂肪酸、丙酸、乙酸与丙酸比值、异丁酸、己酸、异戊酸、总乳酸、d-和l-乳酸以及pH值测量方面未观察到显著的组间变化。在挑战日，BUF组和对照组的乙酸浓度升高。与其他组相比，在挑战时MLY组和MT组的丁酸浓度较低。戊酸浓度在对照组、VM组和BUF组中最低，乳酸浓度在MLY组、VM组和BUF组中在数值上较低。在整个挑战过程中，每组的总乳酸浓度均>10mM。MLY组和MT组的氨浓度较低。MLY组的组胺浓度降低，VM组和BUF组的组胺浓度升高。除了在挑战日对照组、VM组和MT组的生物抗氧化潜力增加外，饲料添加剂在每周或挑战日对血浆氧化应激指标均无影响。尽管动物个体差异较大，但所有饲料添加剂均改变了瘤胃功能，并可能通过不同机制影响酸中毒风险；然而，没有一种添加剂能使所有小母牛的瘤胃稳定。
