Department of Population Health and Reproduction, School of Veterinary Medicine, University of California Davis, 95616.
Department of Population Health and Reproduction, School of Veterinary Medicine, University of California Davis, 95616.
J Dairy Sci. 2020 Dec;103(12):11762-11768. doi: 10.3168/jds.2020-18655. Epub 2020 Oct 9.
Although incidence of clinical hypocalcemia in postpartum dairy cows is low in US dairies, subclinical hypocalcemia after calving is common and has been associated with metabolic and infectious disease. It is widespread farm practice to feed a diet rich in anions to prepartum dairy cattle to support calcium homeostasis. However, this diet is typically discontinued at parturition, when calcium needs are still high. The objective of this trial was to determine the effects of extending metabolic acidification into the first 3 d of lactation in multiparous Holstein cows with the use of magnesium chloride (MgCl) hexahydrate drenches on blood ionized calcium concentrations. Adult Holstein cows at a commercial dairy in their second or higher lactation, with a urine pH of 6.8 or less on the day of calving, were randomly assigned to either treatment or control groups, resulting in 13 cows in the treatment group and 14 cows in the control group. Treatment cows received 480 g of oral MgCl hexahydrate once daily for 3 d for continued acidification starting on the day of calving, whereas cows in the control group received no treatment. Urine pH was measured daily for 5 d, starting on the day of calving (0 DIM), to assess acidification status; blood was collected on day of calving (0 DIM), 2 DIM, and 4 DIM and analyzed for ionized calcium concentrations. Differences in blood ionized calcium and urine pH over time were compared using longitudinal data analysis. Urine pH was lower in treatment cows compared with control cows at 1, 2, and 3 DIM. Blood ionized calcium concentrations were different from baseline, taken at enrollment (0 DIM) and at 2 and 4 DIM in both treatment and control cows. However, no difference was detectable between treatment and control cows at 2 or 4 DIM with respect to blood ionized calcium concentrations. Oral supplementation with MgCl hexahydrate resulted in the desired acidification of urine pH in the treatment group, similar to feeding of an anionic close-up diet. Continued acidification of dairy cows until 2 DIM did not result in clinically meaningful higher blood calcium concentrations compared with controls, and further research is needed, to identify physiological reasons for this finding.
尽管美国奶牛场产后临床低钙血症的发病率较低，但产后亚临床低钙血症很常见，并与代谢和传染性疾病有关。在围产前期给奶牛饲喂富含阴离子的日粮以维持钙稳态是广泛的农场实践。然而，这种日粮通常在分娩时停止，此时钙的需求仍然很高。本试验的目的是确定在产犊后第 1 至 3 天用六水氯化镁（MgCl）灌服来延长代谢酸化对经产荷斯坦奶牛血液离子钙浓度的影响。在商业奶牛场处于第二泌乳期或更高泌乳期的成年荷斯坦奶牛，在产犊当天尿液 pH 值低于 6.8，随机分为处理组或对照组，处理组 13 头奶牛，对照组 14 头奶牛。处理组奶牛从产犊当天开始每天口服 480 g 六水氯化镁，连续酸化 3 天，而对照组奶牛不接受任何治疗。从产犊当天（0 DIM）开始，每天测量尿液 pH 值，连续 5 天，以评估酸化状态；在产犊当天（0 DIM）、第 2 天和第 4 天采集血液并分析离子钙浓度。使用纵向数据分析比较血液离子钙和尿液 pH 值随时间的差异。与对照组相比，处理组奶牛在第 1、2 和 3 天的尿液 pH 值较低。处理组和对照组奶牛的血液离子钙浓度与基线（纳入时，0 DIM）和第 2 天和第 4 天不同。然而，处理组和对照组奶牛在第 2 天或第 4 天的血液离子钙浓度没有差异。六水氯化镁的口服补充使处理组尿液 pH 值达到预期的酸化，类似于阴离子接近日粮的喂养。与对照组相比，奶牛持续酸化至第 2 天并没有导致血液中钙浓度有临床意义的升高，需要进一步研究以确定这一发现的生理原因。
