Natural Resources Institute Finland (Luke), Tietotie 4, 31600 Jokioinen, Finland.
Natural Resources Institute Finland (Luke), Tietotie 4, 31600 Jokioinen, Finland.
Animal. 2024 May;18(5):101146. doi: 10.1016/j.animal.2024.101146. Epub 2024 Mar 27.
Feed utilization efficiency is an important trait in dairy production playing a significant role in reducing feed costs and lowering methane emission. One of the metrics used to measure feed efficiency in dairy cows is residual feed intake (RFI). This metric requires routine measurement of feed intake. Since there is a positive high correlation between heat production and carbon dioxide (CO) production on the one hand and heat production and efficiency on the other hand, residual carbon dioxide (RCO) might be a useful metric to improve feed efficiency. The objectives of this study were to model the trajectories of RCO and RFI as well as to estimate their repeatabilities and correlations at different stages of lactation. Daily CO output and feed intake were recorded from 46 primiparous Nordic Red dairy cows using two Greenfeed Emissions Monitoring™ systems from 2 to 305 days in milk (DIM). Edited data comprised 5 995 daily averages. To calculate predicted values of CO and DM intake (DMI), prediction models were developed by fitting multiple regression models to observations. Subsequently, RCO and RFI were calculated by subtracting predicted values of CO and DMI from their corresponding actual observations. A random regression bivariate model was fitted to estimate repeatabilities and animal correlations within lactation at different DIMs between RCO and RFI traits. The model fitted included fixed effects of year-month of recording, lactation month, fixed regressions as well as random regressions for the animal effect. The residual variance was considered to be heterogeneous. Repeatabilities and animal correlations of RCO and RFI between selected DIM (for every 30 DIM i.e., 6, 36,…, 246 and 276) were calculated. Repeatability of RCO was high at the beginning of lactation (0.72 at DIM 6) and decreased around the peak of milk production (0.27 at DIM 96) and again increased gradually toward the end of lactation. Similarly, RFI also had high repeatability at the beginning (0.86 at DIM 6); however, it decreased in mid-lactation (0.37 at DIM 156) and then increased toward the end of lactation. Animal correlations between RCO and RFI were moderate to high on the same DIM and ranged from 0.37 to 0.88. Overall, we found that animals with higher CO production than expected also consume more DMI than expected, but the moderate correlation between RCO and RFI found in this study calls for more research to assess the potential of RCO to become a new feed efficiency metric.
饲料利用效率是奶牛生产中的一个重要性状，它在降低饲料成本和减少甲烷排放方面起着重要作用。衡量奶牛饲料效率的一个指标是剩余采食量（RFI）。该指标需要常规测量饲料摄入量。由于一方面产热和二氧化碳（CO）的产生与效率之间存在正相关，另一方面产热和 CO 的产生之间存在正相关，因此剩余 CO（RCO）可能是提高饲料效率的有用指标。本研究的目的是建立 RCO 和 RFI 的轨迹模型，并估计其在泌乳不同阶段的重复性和相关性。使用两个 Greenfeed Emissions Monitoring™系统从 2 至 305 天泌乳日（DIM）记录了 46 头北欧红牛初产奶牛的每日 CO 产量和饲料摄入量。经过编辑的数据包含 5995 个每日平均值。为了计算 CO 和干物质采食量（DMI）的预测值，通过拟合多个回归模型对观测值进行了预测模型的开发。随后，通过从相应的实际观测值中减去 CO 和 DMI 的预测值来计算 RCO 和 RFI。通过在不同的 DIM 之间（每隔 30 DIM，即 6、36、…、246 和 276）拟合随机回归二元模型，来估计 RCO 和 RFI 性状在泌乳期内的重复性和动物相关性。模型中包含了记录的年-月、泌乳月、固定回归以及动物效应的随机回归等固定效应。残差方差被认为是异质的。选择的 DIM（每隔 30 DIM，即 6、36、…、246 和 276）的 RCO 和 RFI 的重复性和动物相关性进行了计算。RCO 的重复性在泌乳早期较高（DIM 6 时为 0.72），在产奶高峰期附近降低（DIM 96 时为 0.27），并在泌乳后期逐渐升高。同样，RFI 在泌乳早期也具有较高的重复性（DIM 6 时为 0.86）；然而，它在泌乳中期下降（DIM 156 时为 0.37），然后在泌乳后期升高。在同一 DIM 上，RCO 和 RFI 之间的动物相关性为中等至高度，范围为 0.37 至 0.88。总的来说，我们发现 CO 产生量高于预期的动物也会消耗比预期更多的 DMI，但本研究中发现的 RCO 和 RFI 之间的中等相关性需要进一步研究，以评估 RCO 成为新的饲料效率指标的潜力。
