Residual feed intake (RFI) is defined as the difference between the actual and expected feed intake required to support animal maintenance and growth. Thus, a cow with a low RFI can obtain nutrients for maintenance and growth from a reduced amount of feed compared with a cow with a high RFI. Variation in RFI is underpinned by a combination of factors, including genetics, metabolism, thermoregulation and body composition; hypothalamic-pituitary-adrenal (HPA) axis responsiveness is also a possible contributor. Responses to 3 metabolic challenges were measured in lactating and nonlactating dairy cattle. Sixteen Holstein Friesian cows with phenotypic RFI measurements that were obtained during the growth period (188–220 d old) were grouped as either low-calfhood RFI (n = 8) or high-calfhood RFI (n = 8). An ACTH (2 µg/kg of body weight), insulin (0.12 U/kg), and epinephrine (a low dose of 0.1 µg/kg and a high dose of 1.6 µg/kg of epinephrine) challenge were each conducted during both midlactation (122 ± 23.4 d in milk) and the nonlactating period (dry period; approximately 38 d after cessation of milking). Cows were housed in metabolism stalls for the challenges and were fed a diet of alfalfa cubes ad libitum for at least 10 d before the experiment (lactating cows also were offered a total of 6 kg of dry matter/d of crushed wheat grain plus minerals fed as 3 kg of dry matter at each milking) and were fasted for 12 h before the challenges. The efficiency of conversion of feed into milk (the ratio of feed consumed to milk produced over the 7 d before the experiment) during midlactation was better (lower) in low-calfhood RFI cows, although dry matter intake did not differ between RFI groups. Low-calfhood RFI cows exhibited a lower plasma cortisol response to the ACTH challenge than high-calfhood RFI cows, particularly in midlactation (−15%). The low-calfhood RFI cows had a greater plasma insulin-like growth factor-1 response to the insulin challenge and plasma fatty acid response to epinephrine compared with the high-calfhood RFI cows. These data suggest that high-calfhood RFI cows exhibit a more responsive HPA axis. As divergence in RFI measured during growth is retained (although reduced) during lactation, it is possible that energy is used to respond to HPA axis activation at the expense of production in high-calfhood RFI dairy cattle during lactation and contributes to a decrease in overall feed use efficiency.

剩余饲料摄入量（RFI）定义为支持动物维持和生长所需的实际和预期饲料摄入量之差。因此，与具有高RFI的母牛相比，具有低RFI的母牛可以从减少的饲料量中获得维持和生长所需的营养。RFI的变化受多种因素的影响，包括遗传，代谢，体温调节和身体组成。下丘脑-垂体-肾上腺（HPA）轴反应性也是可能的原因。在哺乳期和非哺乳期的奶牛中，对3种代谢挑战的反应进行了测量。在生长期间（188-220 d龄）获得的具有表型RFI测量值的16头荷斯坦黑白花奶牛被归类为低犊牛RFI（n = 8）或高犊牛RFI（n = 8）。ACTH（2 µg / kg体重），胰岛素（0。在哺乳中期（牛奶中122±23.4 d）和非哺乳期（干燥）分别进行肾上腺素（低剂量的0.1 µg / kg和高剂量的1.6μg/ kg的肾上腺素）攻击。时间；停止挤奶后约38 d）。在实验之前，将母牛关在新陈代谢的小棚里，并随意喂饲紫花苜蓿块至少10 d（也向哺乳的母牛每天提供6千克干物质/粉碎的小麦籽粒和矿物质饲料） （每次挤奶3公斤干物质），并在攻击前禁食12小时。在低犊牛期RFI奶牛的泌乳期，饲料转化为牛奶的效率（实验前7天消耗的饲料与产奶的比例）更好（更低），尽管RFI组之间的​​干物质摄入量没有差异。与高等级RFI奶牛相比，低等级RFI奶牛对ACTH挑战的血浆皮质醇响应更低，尤其是在哺乳期（-15％）。与高等级RFI奶牛相比，低等级RFI奶牛对胰岛素激发的血浆胰岛素样生长因子-1响应更高，对肾上腺素的血浆脂肪酸响应更高。这些数据表明高犊牛RFI奶牛表现出更敏感的HPA轴。由于泌乳过程中生长过程中RFI的差异得以保留（尽管有所降低），因此有可能利用能量来响应HPA轴的激活，而牺牲了泌乳过程中高品位RFI奶牛的生产，并导致总体下降饲料利用效率。特别是在哺乳期（-15％）。与高等级RFI奶牛相比，低等级RFI奶牛对胰岛素激发的血浆胰岛素样生长因子-1响应更高，对肾上腺素的血浆脂肪酸响应更高。这些数据表明高犊牛RFI奶牛表现出更敏感的HPA轴。由于泌乳过程中生长过程中RFI的差异得以保留（尽管有所降低），因此有可能利用能量来响应HPA轴的激活，而牺牲了泌乳过程中高品位RFI奶牛的生产，并导致总体下降饲料利用效率。特别是在哺乳期（-15％）。与高等级RFI奶牛相比，低等级RFI奶牛对胰岛素激发的血浆胰岛素样生长因子-1响应更高，对肾上腺素的血浆脂肪酸响应更高。这些数据表明高犊牛RFI奶牛表现出更敏感的HPA轴。由于泌乳过程中生长过程中RFI的差异得以保留（尽管有所降低），因此有可能利用能量来响应HPA轴的激活，而牺牲了泌乳过程中高品位RFI奶牛的生产，并导致总体下降饲料利用效率。这些数据表明高犊牛RFI奶牛表现出更敏感的HPA轴。由于泌乳过程中生长过程中RFI的差异得以保留（尽管有所降低），因此有可能利用能量来响应HPA轴的激活，而以泌乳期间高品位RFI奶牛的生产为代价，这会导致总体上的下降饲料利用效率。这些数据表明高犊牛RFI奶牛表现出更敏感的HPA轴。由于泌乳过程中生长过程中RFI的差异得以保留（尽管有所降低），因此有可能利用能量来响应HPA轴的激活，而牺牲了泌乳过程中高品位RFI奶牛的生产，并导致总体下降饲料利用效率。