van de Braak A E, van't Klooster A T, Malestein A
Res Vet Sci. 1987 Jan;42(1):101-8.
The influence of a deficient magnesium supply during the dry period on the ability of dairy cows to mobilise calcium at parturition was investigated. The daily rations pre-partum consisted of 6 kg grass hay, and 4 kg concentrates containing either 1.58 per cent magnesium (HMg) or 0.22 per cent magnesium (LMg). Nine cows of parity one to six received the LMg diet and 10 cows of parity one to seven the HMg diet. Both rations provided 1.40 times maintenance on an energy basis and contained 4 per cent potassium in the dry matter. Throughout the dry period the mean concentration of magnesium in the plasma of the LMg group was significantly lower than in the HMg group and at parturition the mean plasma concentrations were 0.65 mmol litre-1 and 1.16 mmol litre-1, respectively. After parturition two cows in the LMg group showed clinical signs of hypocalcaemia but none of the HMg group did so. Cows of the LMg group had a lower mean rate of calcium mobilisation (0.27 mmol min-1) than those of the HMg group (0.34 mmol min-1) but the difference could not be explained by differences in bone turnover as reflected by urinary hydroxyproline excretion. Such a reduced rate of calcium mobilisation may be a contributory factor in the high incidence of milk fever in some herds fed inadequate magnesium in the dry period.
研究了干奶期镁供应不足对奶牛分娩时动员钙能力的影响。产前日粮每日由6千克禾本科干草和4千克精饲料组成，精饲料含镁量分别为1.58%（高镁组，HMg）或0.22%（低镁组，LMg）。9头一胎至六胎的奶牛采食低镁日粮，10头一胎至七胎的奶牛采食高镁日粮。两种日粮在能量方面均提供维持需要量的1.40倍，干物质中含钾4%。在整个干奶期，低镁组奶牛血浆镁的平均浓度显著低于高镁组，分娩时血浆平均浓度分别为0.65毫摩尔/升和1.16毫摩尔/升。产后，低镁组有2头奶牛出现低钙血症的临床症状，而高镁组无此现象。低镁组奶牛的平均钙动员速率（0.27毫摩尔/分钟）低于高镁组（0.34毫摩尔/分钟），但这种差异无法用尿羟脯氨酸排泄所反映的骨转换差异来解释。这种钙动员速率降低可能是某些在干奶期饲喂镁不足的牛群中乳热发病率高的一个促成因素。
