Each year in Australia, 53% of lamb mortalities are attributed to dystocia, with subclinical maternal calcium deficiencies likely contributing to dystocia rates. A negative dietary cation and anion difference (DCAD) diet has increased circulating calcium in sheep. Therefore, this study aimed to investigate the effects of supplementing twin-bearing, grazing ewes with a negative DCAD partial mixed ration (PMR) during late gestation on ewe calcium and magnesium concentrations and subsequent lamb growth and survival. On day 120 of gestation (dG), blood samples were collected from 115 twin-bearing Merino ewes and analyzed for glucose, ketone bodies, pH, ionized calcium, and serum calcium and magnesium. On dG 130, ewes were moved into lambing paddocks and placed in the following 2 treatment groups; ewes receiving a positive DCAD PMR (DCAD = 287 mEq/kg DM; n = 58) and ewes receiving a negative DCAD PMR (DCAD = −125 mEq/kg DM; n = 57) fed as a PMR. On dG 140, a blood and urine sample were collected. The urine was tested for pH. Pasture samples were taken on dG 133 and 149 and tested for DCAD and mineral content. When a lamb was 6 to 18 h old, survival, vigor score, liveweight (LW), rectal temperature, blood glucose, and body morphology were recorded. At 10 d of age, lamb LW and survival were recorded and a milk sample was collected from ewes. At 44 d of age, lamb LW and survival were recorded. The DCAD of the pastures across the 6 paddocks ranged from 598 to 893 mEq/kg DM. There were no differences in lamb survival, weight, or viability at any timepoint (P > 0.05). There were no differences in mineral status, metabolic state, or acid–base balance between the positive and negative DCAD-supplemented ewes (P > 0.05) during supplementation (dG 140). Supplementing a negative DCAD diet to ewes grazing pasture during late gestation did not improve lamb survival. The blood and urine pH of the negative DCAD-supplemented ewes indicated a mild metabolic acidosis was not reached due to the high DCAD of the pastures. Further research needs to take careful consideration of the DCAD of pasture when designing a negative DCAD supplement in order for it to be effective.

中文翻译：

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在妊娠晚期放牧的双胞胎美利奴母羊吃草时，日粮阳离子和阴离子差异的阴性补充不会影响羔羊的生长或存活


在澳大利亚，每年 53% 的羔羊死亡率归因于难产，亚临床母体钙缺乏可能导致难产率。负日粮阳离子和阴离子差异 （DCAD） 日粮增加了绵羊的循环钙。因此，本研究旨在探讨在妊娠晚期用负 DCAD 部分混合日粮 （PMR） 补充双胞胎放牧母羊对母羊钙和镁浓度以及随后的羔羊生长和存活的影响。在妊娠第 120 天 （dG），从 115 只双胞胎美利奴母羊身上采集血样，并分析葡萄糖、酮体、pH 值、离子钙以及血清钙和镁。在 dG 130 上，将母羊转移到产羔围场并分为以下 2 个处理组;接受 DCAD PMR 阳性（DCAD = 287 mEq/kg DM;n = 58）的母羊和接受 DCAD PMR 阴性（DCAD = −125 mEq/kg DM;n = 57）的母羊作为 PMR 饲喂。在 dG 140 上，收集血液和尿液样本。检测尿液的 pH 值。在 dG 133 和 149 上采集牧场样本，并检测 DCAD 和矿物质含量。当羔羊 6 至 18 h 龄时，记录存活率、活力评分、活重 （LW）、直肠温度、血糖和体型学。在 10 d 龄时，记录羔羊 LW 和存活率，并从母羊收集牛奶样本。在 44 日龄时，记录羔羊 LW 和存活率。6 个围场牧场的 DCAD 范围为 598 至 893 mmol/kg 干物质。羔羊存活率、体重或存活率在任何时间点均无差异 （P > 0.05）。补充 DCAD 的阳性和阴性母羊 （P > 0.05） 在补充期间 （dG 140） 的矿物质状态、代谢状态或酸碱平衡没有差异。 在妊娠晚期向放牧牧场的母羊补充阴性 DCAD 饮食并没有提高羔羊的存活率。补充 DCAD 阴性的母羊的血液和尿液 pH 值表明，由于牧场的高 DCAD，没有达到轻度代谢性酸中毒。进一步的研究在设计阴性 DCAD 补充剂时需要仔细考虑牧场的 DCAD，以使其有效。