The objective was to evaluate the effect of the Holstein genotype (North American Holstein vs. New Zealand Holstein; NAH vs. NZH, respectively) in a pasture-based system on heat production (HP), energy partitioning between maintenance and production (milk and tissue) and energy efficiency during two different stages of lactation. Twenty-eight Holstein dairy cows (14 cows of each genotype) with similar calving date (May 5, 2018 ± 23 days) were managed in a pasture-based system and supplemented with one third of the predicted total dry matter intake as concentrate. Heat production, retained energy in milk and tissue, metabolizable energy intake (MEI) and the proportion of MEI retained in milk + tissue (RE/MEI) were measured at 115 and 192 ± 19 days in milk and residual HP was estimated by the difference between measured HP and predicted HP based on NRC (2001) model according to body weight, body condition score and milk production. The NAH cows were 60 ± 15 kg heavier and produced 4.7 ± 1.0 kg/d more milk with lower percentages of fat and protein than NZH cows. However, there were no differences in fat or protein yield per day between genotypes. Metabolizable energy intake, retained energy in milk and tissue, HP and RE/MEI were not different between genotypes at 115 days in milk. Nevertheless, at 192 days in milk the MEI, HP and residual HP were lower in NZH than NAH, whereas RE/MEI was not different when both genotypes were managed under a pasture-based system with one third of the consumed diet as concentrate. The capacity of NZH cows to maintain the same RE/MEI than NAH cows at 192 days in milk despite of the lower MEI, was due to a lower metabolizable energy requirement for maintenance (853 vs. 729 kJ/body weight^0.75 per day for NAH and NZH, respectively). Indeed, the lower energy requirement for maintenance in NZH was associated with a lower fasting heat production since k_l were not different between genotypes. Thus, NZH cows could have a lower proportion of their body as protein mass or a lower relative mass of the internal organs involved with digestive and circulatory functions. However, further investigation is necessary to understand the differences in maintenance energy requirements between the Holstein genotypes.

目的是评估牧场系统中霍尔斯坦基因型（分别为北美霍尔斯坦与新西兰霍尔斯坦；NAH 与 NZH）对热量产生（HP），能量在维持和生产之间分配的影响（牛奶和组织和泌乳两个不同阶段的能量效率。在基于牧场的系统中管理了28头产犊日期相似（2018年5月5日±23天）的荷斯坦奶牛（每种基因型14头奶牛），并补充了预计总干物质摄入量的三分之一作为浓缩物。热量产生，牛奶和组织中的保留能量，代谢能摄入量（MEI）以及牛奶+组织中保留的MEI的比例（RE / MEI）分别在115和192±19天时在牛奶中进行测量，并根据体重，身体状况评分和产奶量，根据NRC（2001）模型根据测得的HP与预测的HP之间的差异估算残留HP。NAH奶牛比NZH奶牛重60±15公斤，日产量增加4.7±1.0公斤/天，脂肪和蛋白质百分比降低。但是，基因型之间每天的脂肪或蛋白质产量没有差异。牛奶中115天的基因型之间，代谢能摄入，牛奶和组织中的残留能量，HP和RE / MEI并无差异。然而，在牛奶中192天时，NZH中的MEI，HP和残留HP低于NAH，而当两种基因型都在基于牧场的系统中进行管理，且食用饮食的三分之一作为浓缩物时，RE / MEI并无差异。与。NAH和NZH分别为729 kJ /体重，每天^0.75）。的确，由于基因型之间的k _l没有差异，因此在NZH中维持较低的能量需求与较低的空腹热量产生有关。因此，NZH奶牛的体内蛋白质含量可能较低，而与消化和循环功能有关的内脏的相对质量可能较低。然而，有必要进一步研究以了解荷斯坦基因型之间维持能量需求的差异。