Hypocalcemia affects almost 50% of all dairy cows. Our laboratory has previously demonstrated that infusions of the serotonin precursor 5-hydroxy-l-tryptophan (5-HTP) increase circulating calcium concentrations in the Holstein transition cow. It is unknown whether feeding a negative DCAD diet alters the relationship between 5-HTP and hypocalcemia. The main objective of this study was to determine whether feeding a negative dietary cation-anion difference (−DCAD) diet before calving in conjunction with 5-HTP treatment could further diminish the magnitude of hypocalcemia at the time of calving. We used a randomized complete block design with a 2 × 2 factorial arrangement. Thirty-one multiparous Holstein cows were fed either a positive (+13 mEq/100 g) or negative (−13 mEq/100 g) DCAD diet 21 d before parturition and were intravenously infused daily with saline or 5-HTP (1 mg/kg) starting 7 d before the estimated date of parturition. Cows were blocked by parity and were randomly assigned to 1 of 4 treatment groups: positive DCAD plus saline, positive DCAD plus 5-HTP, negative DCAD plus saline, and negative DCAD plus 5-HTP, resulting in n = 8 per group. Total calcium (tCa), ionized calcium (iCa), and feed intake were recorded. The iCa was elevated prepartum in the −DCAD/5-HTP group compared with the other treatment groups as well as on d 0 and 1 postpartum. Although differences in tCa were not significant across the pre- or postpartum periods, tCa was numerically higher on d 0 and significantly higher on d 1 in −DCAD/5-HTP cows compared with all other groups. Prepartum the −DCAD/5-HTP treatment group ate less than the other treatment groups; however, postpartum dry matter intake differences were not significant. These findings demonstrate that feeding a −DCAD diet in conjunction with 5-HTP prepartum can increase postpartum circulating iCa concentrations and therefore diminish the magnitude of hypocalcemia at the time of parturition.

低血钙症影响几乎所有奶牛的50％。我们的实验室已先前证明血清素前体5-羟基的是输注升-色氨酸（5-HTP）增加荷斯坦奶牛的循环钙浓度。喂养DCAD饮食阴性是否会改变5-HTP与低血钙之间的关系还不得而知。这项研究的主要目的是确定在产犊前与5-HTP治疗联合饲喂负的饮食阳离子负离子差异（-DCAD）饮食是否可以进一步减少产犊时低钙血症的程度。我们使用2×2析因排列的随机完整块设计。在分娩前21天，对31只多头荷斯坦奶牛饲喂正（+13 mEq / 100 g）或负（−13 mEq / 100 g）DCAD日粮，并每天静脉输注生理盐水或5-HTP（1 mg /公斤）在预计分娩日期前7天开始。母牛被胎次所阻断，被随机分配到4个治疗组中的1个：DCAD阳性加生理盐水，DCAD阳性加5-HTP阳性，DCAD阴性加生理盐水和DCAD加上5-HTP阴性，每组n = 8。记录总钙（tCa），离子钙（iCa）和采食量。与其他治疗组以及产后第0天和第1天相比，−DCAD / 5-HTP组的产前iCa升高。尽管在产前或产后期间tCa的差异不显着，但与所有其他组相比，-DCAD / 5-HTP奶牛的tCa在d 0时数值更高，在d 1时数值更高。产前−DCAD / 5-HTP治疗组的饮食少于其他治疗组；但是，产后干物质摄入差异不显着。