Synergy Effects Of Lowering Dietary Cation-anion Difference With V_D And Mg Supplementation On Hypocalcemia Prevention

Reducing dietary cation-anion difference?dietary cation-anion difference,DCAD; mmol/kg DM? has been a common way to increase blood calcium content and then prevent hypocalcemia. 1,25-?OH?₂D₃ is the biologically active form of V_D,Mg is an important factor in regulating PTH secretion. Both of them are controller for dietary Ca absorption. In this paper, goats were used as experimental animals to evaluate the effects of lowering DCAD with V_D or Mg supplementation on hypocalcemia prevention. Three trials were carried out in the study.Part 1 was conducted to examine the effects of varying DCAD diets on acid-base balance, plasma calcium homeostasis and its regulatory metabolites levels, and performance of goats. Eighteen healthy female goats, which had similar good body condition and weight, were select as experimental animals and were randomly divided into 3 blocks of 6 goats. Levels of DCAD for control, treatment 1, and treatment 2were 120,-25, and-170, respectively. The trial duration last 40 d including 10-d prefeeding and 30-d trial phases. Nutrients digestibility; urine acid-base balance; and plasma levels of Ca²⁺, P, PTH, CT, 1,25-?OH?₂VD₃, VDR, CaBP-D9 k, and TRPV6 were detected. The results showed that:?1? Treatment 1 had the quickest feed intake speed and consumed the highest DMI level, indicating significant difference over control and treatment 2?P<0.05?. Nutrients digestibility of DM, EE, and NDF were higher in control over treatment 2?P<0.05?. Treatment 2 resulted in lower digestibility of CP and ADF than control and treatment 1?P<0.05?.?2? Urine pH was found to be gradually decreased within the decreasing of DCAD levels?P<0.05?, and there was a significant association between urine pH and DCAD?R2=0.7439, P<0.05?.?3? Plasma Ca for treatment 2 was higher than control?P<0.05?. Decreasing the levels of DCAD in variation of plasma P, PTH, 1,25-?OH?₂VD₃ level?P>0.05?, but significantly decreased CT?P<0.05?.?4? Plasma levels of VDR, CaBP-D9 k, TRPV6 were found gradually increased with the order of control, treatment 1, and treatment 2.Goats fed treatment 2 had higher plasma VDR and CaBP-D9 k content than that of control?P<0.05?.?5? There was a significant correlation between plasma Ca, VDRand CaBP-D9 k, and between plasma VDR and CaBP-D9k?P<0.001?. The above results indicated that reducing DCAD could acidify goats' fluid acid-base balance,increased the concentration of calmodulin?VDR, CaBP-D9k? in plasma, reduced the content of plasma CT, improved the level of blood calcium and then prevent hypocalcemia.The work in part 2 was aimed at evaluate the effects of low DCAD plus V_D on plasma levels of Ca and modulators-related with Ca, and growth performance for goats. The trial was carried out by random block design. Eighteen pregnant goats,with similar age and body weight, were randomly divided into 3 groups of 6 goats:control, treatment 1, and treatment 2. The DCAD level for goats was 200,-150,-150,respectively. Anion salts?MgCl2·6H2O? was added in treatment 1 to reduce DCAD level, V_D were added in treatment 2. Duration for the experiment was 40 d including10-d prefeeding and 30-d trial phases. Dry matter intake, daily gain weight, and ratio of feed to gain?F/G?; plasma concentrations of Ca, P, PTH, CT, 1,25-?OH?₂VD₃, VDR,and CaBP-D9 k were measured. The results showed that:?1? Urine pH values in treatment 1 and treatment 2 was remarkably lower than that of control?P<0.05?.?2?The 2 treatment diets resulted in no significant difference for the growth performance measurements DMI, ADG, and F/G?P>0.05?.?3? Plasma Ca and 1,25-?OH?₂VD₃levels were increased for treatment 2 relative to control and treatment 1?P<0.05?,while no significant difference between control and treatment 1?P>0.05?. Plasma P and PTH levels showed no difference among 3 treatments?P>0.05?, plasma CT was tended to reduce in treatment 2 over treatment 1?P<0.1?.?4? The combination of anion salts and V_D for treatment 2 resulted in higher plasma VDR, CaBP-D9 k and TRPV6 than that of control?P<0.05?. It was indicated that feeding low DCAD plus V_D could further improve the content of regulatory factors of blood Ca, including1,25-?OH?₂VD₃, VDR, CaBP-D9 k, TRPV6, which would be beneficial to maintenance the balance of blood Ca.The objective of part 3 was to analyze the effect of low DCAD with Mg?MgO?on nutrition digestibility, rumen fermentation, and plasma levels of Ca and its modulators of goats. Six healthy goats were allocated to 2×3 cross-over designaccording to their similar age and body weight. Goats were assigned to ontrol and treatmen with 3 individual goats, respectively. Experimental last 30 days including 2phases. Each phase last for 15 days with 14-day adaptation and 1-day sampling duration. Nutrients digestibility; urine pH; plasma levels of Ca, Mg, 1,25-?OH?₂VD₃,PMCA1 b, VDR, CaBP-D9 k, and PTH; and rumen pH, NH3-N, buffering capacity,cellulases?microcrystalline cellulose, carboxymethyl cellulose, xylanase, and cellobiase? activity, and VFA levels were measured in the trial. The results were shown as follows,?1? Goats fed treatment diet had reduced DM, EE, CP, NDF, and Ash digestibility; among which DM and EE reaching significant difference?P<0.05?.?2? Addition of anion salts and MgO resulted in no difference for ruminal pH, NH3-N concentration and VFA level?P>0.05?. Ruminal buffering capacity in treatment was higher than that of control?P<0.05?. Cellobiase activity for treatment was higher compared with control?P<0.05?, whereas there was no difference for microcrystalline cellulose, carboxymethyl cellulose, and xylanase for 2 groups?P>0.05?.?3? The concentration of Ca²⁺, Mg²⁺, 1,25-?OH?₂VD₃, PMCA1 b in plasma were increased after adding anion salts and Mg?P<0.05?. There was no significant difference for plasma VDR, CaBP-D9 k, PTH between 2 groups?P>0.05?. It was suggested that adding anion salts and Mg reduced nutrients digestibility, but improve rumen environment and enhance blood Ca level, therefore, was beneficial to maintenance of blood Ca.In conclusion, feeding low DCAD plus with V_D and Mg supplementation could further improve blood Ca and part of Ca-related with modulators?VDR, CaBP-D9 k,1,25-?OH?₂VD₃, TRPV6? levels. This is more effective to maintain blood Ca homeostasis and then for hypocalcemia prevention. Mg supplementation had not side effect on rumen fermentation.