NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle, NSW, Australia.
NSW Department of Primary Industries, Agricultural Research Centre, Trangie, NSW, Australia.
J Anim Sci. 2018 Nov 21;96(11):4859-4867. doi: 10.1093/jas/sky308.
Angus cattle from 2 beef cattle projects on which carbon dioxide production rate (CPR) was measured were used in this study to examine the relationships among BW, DMI, and carbon dioxide traits of beef cattle fed ad libitum on a roughage diet or a grain-based feedlot diet, and to evaluate potential proxies for DMI and feed efficiency. In both projects, the GreenFeed Emission Monitoring system, which provides multiple short-term breath measures of carbon dioxide production, was used as a tool to measure CPR. The data were from 119 Angus heifers over 15 d on a roughage diet and 326 Angus steers over 70 d on a feedlot diet. Mean (±SD) age, BW, and DMI were 372 ± 28 d, 355 ± 37 kg, and 8.1 ± 1.3 kg/d for the heifers, and 554 ± 86 d, 577 ± 69 kg, and 13.3 ± 2.0 kg/d for the steers, respectively. The corresponding mean CPR was 5760 ± 644 g/d for heifers and 8939 ± 1212 g/d for steers. Other traits studied included carbon dioxide yield (CY; CPR/DMI) and intensity (CI; CPR/BW) and 5 forms of residual carbon dioxide production (RCP), which is a measure of actual minus predicted CPR. Feed efficiency traits studied included feed conversion ratio (FCR) and residual feed intake (RFI). The relationship between CPR and DMI, and between CPR and BW was both positive and linear, for the heifers and also for the steers. For the combined heifer and steer datasets, the R2 for the relationship between CPR and BW, and between CPR and DMI was 0.82 and 0.78, respectively. The correlation between CPR and DMI (r = 0.84 for heifers; r = 0.83 for steers) was similar to that between CPR and BW (r = 0.84 for heifers; r = 0.87 for steers). Most of the carbon dioxide traits were significantly (P < 0.05) correlated with one or both feed efficiency traits. One of the RCP traits (RCPMA) was computed by maintaining metabolic BW (M) and average daily gain (A) in the formula for RFI, but substituting the DMI with CPR. The correlation (r = 0.27) between RCPMA and RFI, though significantly different from zero, was not strong enough for its use as proxy for RFI. On the other hand, a strong correlation (r = 0.73) was obtained between the CPR to gain ratio (CGR) and FCR. This indicates that, where DMI is not available, CPR could be used in its place to compute a feed efficiency trait similar to FCR, since the computation of CGR was similar to that for FCR, except that DMI was substituted with CPR in the FCR formula.
本研究利用来自 2 个肉牛项目的安格斯牛（ Angus cattle ），这些项目均对二氧化碳产生速率（CPR）进行了测量，旨在研究自由采食粗饲料或谷物型肥育日粮的肉牛的体重（BW）、采食量（DMI）和二氧化碳特征之间的关系，并评估 DMI 和饲料效率的潜在替代指标。在这两个项目中，都使用了 GreenFeed Emission Monitoring 系统，该系统提供了多种短期二氧化碳产生的测量，作为测量 CPR 的工具。数据来自于 15 天粗饲料日粮的 119 头安格斯小母牛和 70 天谷物型肥育日粮的 326 头安格斯阉牛。小母牛的平均（±SD）年龄、BW 和 DMI 分别为 372 ± 28 d、355 ± 37 kg 和 8.1 ± 1.3 kg/d，阉牛的分别为 554 ± 86 d、577 ± 69 kg 和 13.3 ± 2.0 kg/d。相应的平均 CPR 分别为小母牛的 5760 ± 644 g/d 和阉牛的 8939 ± 1212 g/d。研究的其他特征包括二氧化碳产量（CY；CPR/DMI）和强度（CI；CPR/BW）以及 5 种剩余二氧化碳产生形式（RCP），这是实际与预测 CPR 之间的差值。研究的饲料效率特征包括饲料转化率（FCR）和剩余饲料摄入量（RFI）。CPR 与 DMI 之间以及与 BW 之间的关系在小母牛和阉牛中均呈正线性关系。在小母牛和阉牛的组合数据集上，CPR 与 BW 之间以及与 DMI 之间的关系的 R2 分别为 0.82 和 0.78。CPR 与 DMI 之间的相关性（小母牛的 r = 0.84；阉牛的 r = 0.83）与 CPR 与 BW 之间的相关性（小母牛的 r = 0.84；阉牛的 r = 0.87）相似。大多数二氧化碳特征与一个或两个饲料效率特征显著相关（P < 0.05）。其中一个 RCP 特征（RCPMA）是通过在 RFI 公式中保持代谢 BW（M）和平均日增重（A）来计算的，但用 CPR 替代了 DMI。RCPMA 与 RFI 之间的相关性（r = 0.27）虽然与零显著不同，但还不够强，不能作为 RFI 的替代指标。另一方面，CPR 与增重比（CGR）和 FCR 之间存在很强的相关性（r = 0.73）。这表明，在无法获得 DMI 的情况下，可以使用 CPR 来计算类似于 FCR 的饲料效率特征，因为 CGR 的计算与 FCR 相似，只是在 FCR 公式中用 CPR 替代了 DMI。
