Department of Animal Sciences, University of Florida, Gainesville 32608.
Department of Animal Sciences, University of Florida, Gainesville 32608.
J Dairy Sci. 2022 Apr;105(4):3090-3101. doi: 10.3168/jds.2021-20995. Epub 2022 Feb 3.
The objective of this study was to evaluate the effects of replacing magnesium oxide (MgO) with calcium-magnesium carbonate [CaMg(CO)] on ruminal fermentation with or without the addition of sodium bicarbonate (NaHCO). Eight fermentors of a dual-flow continuous-culture system were distributed in a replicated (2) 4 × 4 Latin square design in a 2 × 2 factorial arrangement of treatments (magnesium sources × NaHCO). The treatments tested were 0.21% MgO [MgO; dry matter (DM) basis; 144.8 mEq of dietary cation-anion difference (DCAD)]; 0.21% MgO + 0.50% NaHCO (MgO+NaHCO; DM basis; 205.6 mEq of DCAD); 1.00% CaMg(CO) [CaMg(CO); DM basis; 144.8 mEq of DCAD]; and 1.00% CaMg(CO) + 0.50% NaHCO [CaMg(CO)+NaHCO; DM basis; 205.6 mEq of DCAD]. Diets were formulated to have a total of 0.28% of Mg (DM basis). The experiment consisted of 40 d, which was divided into 4 periods of 10 d each, where 7 d were used for adaptation and 3 d for sampling to determine pH, volatile fatty acids (VFA), ammonia (NH-N), lactate, mineral solubility, N metabolism, and nutrient digestibility. The effects of Mg source [MgO vs. CaMg(CO)], NaHCO (with vs. without), and the interaction were tested with the MIXED procedure of SAS version 9.4 (SAS Institute). There was no Mg source × NaHCO interaction in the pH variables and mineral solubility, and Mg sources evaluated did not affect the variables related to ruminal pH and solubility of Mg. On the other hand, the inclusion of NaHCO increased the pH daily average, independent of Mg source, which led to a reduced time that pH was below 5.8 and decreased area under the curve. Total VFA and lactate concentration were similar among treatments regardless of NaHCO and Mg source; however, the molar proportion of isobutyrate and NH-N concentration were lower in diets with CaMg(CO) compared with MgO. Moreover, NaHCO inclusion increased NH-N, total daily NH-N flow, isobutyrate concentration, and acid detergent fiber digestibility. Our results showed that CaMg(CO) leads to a lower NH-N concentration and isobutyrate proportion. Therefore, because most of the tested variables were not significantly different between MgO and CaMg(CO) when combined or not with NaHCO, CaMg(CO) can be a viable alternative source to replace MgO in dairy cow diets without affecting mineral solubility, ruminal pH, nutrient digestibility, total VFA, and the main ruminal VFA. Although Mg sources are known to have an alkalizing effect, NaHCO inclusion in diets with Mg supplementation allowed an increase in ruminal pH, as well as an increase in isobutyrate and NH-N flow.
本研究旨在评估用钙镁碳酸盐[CaMg(CO)]代替氧化镁（MgO）对添加或不添加碳酸氢钠（NaHCO）的瘤胃发酵的影响。在一个重复（2）4×4 拉丁方设计的 2×2 因子处理安排中，8 个双流量连续培养系统发酵罐分布在一个双流量连续培养系统中（镁源×NaHCO）。试验处理为 0.21%MgO[MgO；干物质（DM）基础；144.8 毫当量的日粮阳离子-阴离子差（DCAD）]；0.21%MgO+0.50%NaHCO（MgO+NaHCO；DM 基础；205.6 毫当量的 DCAD）；1.00%CaMg(CO)[CaMg(CO)；DM 基础；144.8 毫当量的 DCAD]；和 1.00%CaMg(CO)+0.50%NaHCO[CaMg(CO)+NaHCO；DM 基础；205.6 毫当量的 DCAD]。日粮的镁含量设定为 0.28%（DM 基础）。试验分为 40 天，分为 4 个 10 天的时期，其中 7 天用于适应，3 天用于采样，以确定 pH 值、挥发性脂肪酸（VFA）、氨（NH-N）、乳酸、矿物质溶解度、氮代谢和养分消化率。用 SAS 版本 9.4（SAS 研究所）的 MIXED 程序检验镁源[MgO 与 CaMg(CO)]、NaHCO（有与无）和交互作用的影响。在 pH 值变量和矿物质溶解度方面，没有发现镁源×碳酸氢钠的互作，所评价的镁源对与瘤胃 pH 值和镁溶解度相关的变量没有影响。另一方面，无论镁源如何，添加 NaHCO 都能使每日 pH 值平均值升高，这导致 pH 值低于 5.8 的时间减少，曲线下面积减少。无论是否添加 NaHCO 和镁源，总 VFA 和乳酸浓度在处理间均相似；然而，与 MgO 相比，用 CaMg(CO)时，异丁酸和 NH-N 浓度的摩尔比例较低。此外，添加 NaHCO 增加了 NH-N、总日 NH-N 流量、异丁酸浓度和酸性洗涤剂纤维消化率。我们的结果表明，CaMg(CO)可降低 NH-N 浓度和异丁酸比例。因此，由于在添加或不添加 NaHCO 时，MgO 和 CaMg(CO)之间的大多数测试变量均无显著差异，因此 CaMg(CO)可作为奶牛日粮中替代 MgO 的可行来源，而不会影响矿物质溶解度、瘤胃 pH 值、养分消化率、总 VFA 和主要瘤胃 VFA。虽然镁源已知具有碱化作用，但在添加镁的日粮中添加 NaHCO 可增加瘤胃 pH 值，并增加异丁酸和 NH-N 流量。
