Veterinary Physiology, Vetsuisse Faculty, University of Bern, 3012 Bern, Switzerland.
Veterinary Physiology, Vetsuisse Faculty, University of Bern, 3012 Bern, Switzerland.
Animal. 2021 Jul;15(7):100306. doi: 10.1016/j.animal.2021.100306. Epub 2021 Jun 25.
Short-term imbalances of dietary nutrients occur during natural fluctuations in roughage quality (e.g. on pasture) or temporal shortages of supplementary feed components. In contrast to a deficiency, macronutrients (i.e. carbohydrates, proteins, lipids) beyond the adequate supply with other nutrients may, for instance, alter milk composition, increase BW or result in a greater excretion of nitrogen. Especially dairy cows with a moderate performance, in mid- or late lactation, or in extensive farming systems may be exposed to imbalanced rations. A better understanding of metabolic and endocrine responses depending on macronutrient supply may help to precisely feed dairy cows. The present study investigated short-term metabolic and endocrine responses to different levels of concentrates formulated to particularly provide one major macronutrient source (carbohydrates, proteins or lipids). Based on parity number, lactational stage, milk yield and BW, nine mid-lactating cows (211 ± 19 days in milk) were grouped into three blocks of three animals each. Concentrates (aminogenic: rich in CP and nitrogen sources; glucogenic: high content of carbohydrates and glucogenic precursors; lipogenic: high lipid content) were fed in addition to hay in a factorial arrangement at increasing levels from 2.5 to 7.5 kg/d during 9 d. Milk yield, BW and feed intake were recorded daily. Blood and milk were sampled every 3 d at the end of each concentrate level. Milk fat, protein, lactose and urea contents were determined. In blood, concentrations of various metabolites, endocrine factors and enzyme activities (e.g. glucose, non-esterified fatty acids (NEFAs), β-hydroxybutyrate, urea, cholesterol, triglycerides, insulin, glucagon, aspartate aminotransferase (ASAT), gamma-glutamyltransferase (GGT) and glutamate dehydrogenase activity (GLDH)) were measured. Milk yield, milk composition and BW were not affected by type and level of concentrates. Feed intake increased in cows with greater amounts of the aminogenic and lipogenic concentrate compared with the glucogenic concentrate. Milk and plasma urea concentrations were elevated in the aminogenic and to a lesser extent in the lipogenic treatment compared with the glucogenic treatment. Glucose concentrations in plasma were not affected by treatments, whereas insulin and glucagon increased, and NEFA concentrations decreased only in cows fed 7.5 kg/d aminogenic concentrate compared with the glucogenic and lipogenic treatment. Activities of ASAT, GGT and GLDH as well as the total antioxidant capacity were not affected by diets. In conclusion, immediate metabolic and endocrine responses were observed due to the short-term dietary changes. Particularly, a surplus of nitrogen supply via the aminogenic diet affected metabolic responses and stimulated insulin and glucagon secretion.
短期的饮食营养不平衡会发生在粗饲料质量的自然波动（例如在牧场上）或补充饲料成分的暂时短缺时。与缺乏不同，超过其他营养素充足供应的大量营养素（即碳水化合物、蛋白质、脂质）可能会改变牛奶成分、增加体重或导致更多的氮排泄。特别是处于中等性能、泌乳中期或后期或在广泛养殖系统中的奶牛可能会接触到不平衡的日粮。更好地了解代谢和内分泌对大量营养素供应的反应可能有助于更精确地喂养奶牛。本研究调查了不同水平的浓缩物对短期代谢和内分泌反应的影响，这些浓缩物专门提供一种主要的大量营养素来源（碳水化合物、蛋白质或脂质）。根据胎次数、泌乳阶段、产奶量和体重，将 9 头泌乳中期奶牛（泌乳 211±19 天）分为 3 个 3 头动物的块，每个块。在干草之外，以因子设计方式添加精料，从 2.5 至 7.5kg/d 逐步增加水平，持续 9 天。每天记录产奶量、体重和采食量。在每个浓缩物水平结束时每 3 天采集一次血液和牛奶样本。测定牛奶脂肪、蛋白质、乳糖和尿素含量。血液中各种代谢物、内分泌因子和酶活性（如葡萄糖、非酯化脂肪酸（NEFA）、β-羟丁酸、尿素、胆固醇、甘油三酯、胰岛素、胰高血糖素、天冬氨酸氨基转移酶（ASAT）、γ-谷氨酰转移酶（GGT）和谷氨酸脱氢酶活性（GLDH））的浓度。浓缩物的类型和水平对产奶量、牛奶成分和体重没有影响。与葡萄糖相比，摄入更多的氨基和脂类浓缩物的奶牛采食量增加。与葡萄糖处理相比，氨基和脂类处理组的牛奶和血浆尿素浓度升高，而氨基处理组的浓度升高较小。处理组对血浆葡萄糖浓度没有影响，而胰岛素和胰高血糖素增加，只有摄入 7.5kg/d 氨基浓缩物的奶牛的 NEFA 浓度降低与葡萄糖和脂类处理相比。天冬氨酸氨基转移酶、GGT 和 GLDH 的活性以及总抗氧化能力不受饮食影响。总之，由于短期饮食变化，观察到了即时的代谢和内分泌反应。特别是，通过氨基饮食过量供应氮会影响代谢反应并刺激胰岛素和胰高血糖素的分泌。
