Department of Animal Science, University of Nebraska-Lincoln, Lincoln 68583.
Department of Biological Systems Engineering, University of Nebraska-Lincoln, Lincoln 68583.
J Dairy Sci. 2021 Jan;104(1):346-356. doi: 10.3168/jds.2020-18976. Epub 2020 Nov 12.
Heat production (HP) represents a major energy cost in lactating dairy cows. Better understanding of factors that affect HP will improve our understanding of energy metabolism. Our objective was to derive models to explain variation in HP of lactating Jersey cows. Individual animal-period data from 9 studies (n = 293) were used. The data set included cows with a wide range (min to max) in days in milk (44-410) and milk yield (7.8-43.0 kg/d). Diets included corn silage as the predominate forage source, but diets varied (min to max on DM basis) in crude protein (CP; 15.2-19.5%), neutral detergent fiber (NDF; 35.5-43.0%), starch (16.2-31.1%), and crude fat (2.2 to 6.4%) contents. Average HP was (mean ± standard deviation) 22.1 ± 2.86 Mcal/d, or 28.1 ± 3.70% of gross energy intake. Eight models were fit to explain variation in HP: (1) dry matter intake (DMI; INT); (2) milk fat, protein, and lactose yield (MILKCOMP); (3) INT and milk yield (INT+MY); (4) INT and MILKCOMP/DMI (INT+MILKCOMP); (5) mass of digested NDF, CP, and starch (DIG); (6) INT and digested energy (INT+DE); (7) INT and NDF, CP, and starch digestibility (INT+DIG); or (8) INT+MILKCOMP model plus urinary N excretion (INT+MILKCOMP+UN). For all HP models, metabolic body weight was included. All models were derived via a backward elimination approach and included the random effects of study, cow, and period within block within study. The INT models adequately explained variation in HP with a nonrandom effect-adjusted concordance correlation coefficient of 0.84. Similar adjusted concordance correlation coefficients (0.79-0.85) were observed for other HP models. The HP associated with milk protein yield and supply of digestible protein was greater than other milk production and nutrient digestibility variables. The HP associated with urinary N excretion was 5.32. Overall, HP can be adequately predicted from metabolic body weight and DMI. Milk component yield, nutrient digestibility, or urinary N excretion explained similar variation as DMI. Coefficients for milk protein and protein digestion suggest that digestion and metabolism of protein and synthesis of milk protein contribute substantially to HP of a dairy cow.
产热量（HP）是泌乳奶牛的主要能量消耗。更好地了解影响 HP 的因素将有助于我们了解能量代谢。我们的目的是建立模型来解释泽西泌乳奶牛 HP 的变化。使用了 9 项研究（n=293）的个体动物-时期数据。该数据集包括产奶天数（44-410）和产奶量（7.8-43.0kg/d）差异较大的奶牛。日粮以玉米青贮料为主要粗饲料来源，但日粮（干物质基础上）的粗蛋白（CP；15.2-19.5%）、中性洗涤纤维（NDF；35.5-43.0%）、淀粉（16.2-31.1%）和粗脂肪（2.2-6.4%）含量存在差异。平均 HP 为（平均值±标准差）22.1±2.86Mcal/d，或总摄入能量的 28.1±3.70%。拟合了 8 个模型来解释 HP 的变化：（1）干物质采食量（DMI；INT）；（2）乳脂、乳蛋白和乳糖产量（MILKCOMP）；（3）DMI 和产奶量（INT+MY）；（4）DMI 和 MILKCOMP/DMI（INT+MILKCOMP）；（5）可消化 NDF、CP 和淀粉的质量（DIG）；（6）DMI 和消化能（INT+DE）；（7）DMI 和 NDF、CP 和淀粉消化率（INT+DIG）；或（8）INT+MILKCOMP 模型加尿氮排泄（INT+MILKCOMP+UN）。对于所有 HP 模型，代谢体重均包含在内。所有模型均通过后向消去法得出，并包含研究、牛和试验内块内周期的随机效应。INT 模型可以很好地解释 HP 的变化，非随机效应调整后的一致性相关系数为 0.84。其他 HP 模型也观察到了类似的调整后一致性相关系数（0.79-0.85）。与其他牛奶生产和营养消化变量相比，与牛奶蛋白产量和可消化蛋白供应相关的 HP 更大。与尿氮排泄相关的 HP 为 5.32。总的来说，HP 可以通过代谢体重和 DMI 进行充分预测。乳成分产量、养分消化率或尿氮排泄与 DMI 解释了相似的变化。牛奶蛋白和蛋白质消化的系数表明，蛋白质的消化和代谢以及牛奶蛋白的合成对奶牛的 HP 有很大贡献。
