Two studies were designed to evaluate the relative bioavailability of l-carnitine delivered by different methods in dairy cattle. In experiment 1, 4 Holstein heifers were used in a split-plot design to compare ruminally or abomasally infused l-carnitine. The study included 2 main-plot periods, with infusion routes allocated in a crossover design. Within main-plot periods, each of 3 subplot periods consisted of 4-d infusions separated with 4-d rest periods. Subplot treatments were infusion of 1, 3, and 6 g of l-carnitine/d in conjunction with 6 g/d of arabinogalactan given in consideration of eventual product manufacturing. Doses increased within a period to minimize carryover risk. Treatments were solubilized in 4 L of water and delivered in two 10-h infusions daily. Blood was collected before the start of infusion period and on d 4 of each infusion period to obtain baseline and treatment l-carnitine concentrations. There was a dose × route interaction and route effect for increases in plasma carnitine above baseline, with increases above baseline being greater across all dose levels when infused abomasally compared with ruminally. Results demonstrated superior relative bioavailability of l-carnitine when ruminal exposure was physically bypassed. In experiment 2, 56 lactating Holstein cows (143 ± 72 d in milk) were used in 2 cohorts in randomized complete block designs (blocked by parity and milk production) to evaluate 2 rumen-protected products compared with crystalline l-carnitine. Treatments were (1) control, (2) 3 g/d of crystalline l-carnitine (crystalline), (3) 6 g/d of crystalline, (4) 5 g/d of 40COAT (40% coating, 60% l-carnitine), (5) 10 g/d of 40COAT, (6) 7.5 g/d of 60COAT (60% coating, 40% l-carnitine), and (7) 15 g/d of 60COAT. Treatments were top-dressed to diets twice daily. Each cohort used 14-d and included a 6-d baseline measurement period with the final 2 d used for data and sample collection, and an 8-d treatment period with the final 2 d used for data and sample collection. Plasma, urine, and milk samples were analyzed for l-carnitine. Crystalline and 40COAT linearly increased plasma l-carnitine, and 60COAT tended to linearly increase plasma l-carnitine. Total excretion (milk + urine) of l-carnitine averaged 1.52 ± 0.04 g/d in controls, increased linearly with crystalline and 40COAT, and increased quadratically with 60COAT. Crystalline increased plasma l-carnitine and l-carnitine excretion more than 40COAT and 60COAT. In conclusion, preventing ruminal degradation of l-carnitine increased delivery of bioavailable carnitine to cattle, but effective ruminal protection and postruminal bioavailability is challenging.

两项研究旨在评估的相对生物利用度升在奶牛不同的方法传递肉碱。在实验1中，4头荷斯坦母牛在裂区设计用于比较瘤胃或输注皱胃升肉碱。该研究包括2个主要情节时期，并在交叉设计中分配了输液途径。在主图周期内，3个子图周期中的每个周期均由4 d输液和4 d静息期分隔而成。子图处理是输注1、3和6 g的l-肉碱/ d结合6 g / d的阿拉伯半乳聚糖考虑到最终产品的生产。一定时间内增加剂量，以最大程度地减少结转风险。将治疗剂溶于4 L水中，每天两次输注10小时。在输液期开始之前和每个输液期的第4天收集血液，以获得基线和治疗中的1-肉碱浓度。血浆肉碱水平高于基线时，存在剂量×途径相互作用和途径效应，与反刍动物相比，在所有剂量水平上，高于所有剂量水平的基线时肉碱的增加幅度更大。结果表明，l具有较高的相对生物利用度-肉碱绕过瘤胃暴露时的-肉碱。在实验2中，56泌乳荷斯坦奶牛（143±72 d在牛奶）在随机化完全区组设计（阻断奇偶校验和产奶量）与结晶相比，评价2瘤胃-被保护的产品2组群中使用升肉碱。处理为（1）对照，（2）3克/结晶的d升肉碱（结晶），（3）6克结晶/ d，（4）5克/ 40COAT的d（40％涂层，60％升-肉碱），（5）10克/天的40COAT，（6）7.5克/天的60COAT（60％涂层，40％l-肉碱），以及（7）15克/天的60COAT。每天两次对饮食进行追肥。每个队列使用14天，包括6天基线测量期，最后2天用于数据和样本收集，以及8天治疗期，最后2天用于数据和样本收集。血浆，尿液和牛奶样本进行了分析升肉碱。结晶和40COAT线性增加血浆升肉碱，和60COAT趋于线性增加等离子体升肉碱。的总排泄（牛奶+尿）升肉碱平均1.52±0.04克/ d在对照中，用结晶和40COAT线性增加，并用二次方60COAT增加。结晶增加血浆升肉碱和升-肉碱排泄超过40COAT和60COAT。总之，预防的瘤胃降解升肉碱提高生物利用度交货肉碱牛，但有效的瘤胃保护和瘤胃生物利用度是一个挑战。