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Reducing dietary cation-anion difference increased gastrointestinal calcium binding proteins-D9k expression level of transition goats for plasma calcium absorption
The mechanism why reducing dietary cation-anion difference (DCAD, mEq/kg DM) could prevent hypocalcemia in transition dairy cows remains unclear. Calcium binding protein-9kDa (CaBP-D9k) was the main biological factor highly associated with Ca absorption in the gastrointestinal tract (GIT; rumen, reticulum, omasum, abomasum, jejunum, ileum, colon, cecum, and rectum). This study was conducted to clarify the mechanism by investigating the influence of varying DCAD level on CaBP-D9k expression level in GIT and plasma Ca concentration of transition goats, which had similar anatomy and metabolic process relative to dairy cows. Twenty-seven transition goats were randomly allocated to 1 of 3 treatments and were fed 1 of 3 diets with varying DCAD levels: +300 (HD), +150 (CON), and -50 (LD), respectively. Goats were bled on d 10 before lambing, d 0 for lambing, and d 3 after lambing to determine plasma ions contents; and were slaughtered to detect the CaBP-D9k expression level, respectively. Dry matter intake was unaffected by DCAD treatments (P>0.05). Urine pH was reduced with decreasing DCAD level (P<0.05). The LD diet level induced higher plasma Cl- and Ca2+ concentrations relative to CON and HD diets (P<0.05). Greater CaBP-D9k mRNA expression level was observed in whole GIT of LD-fed goats except for ileum, cecum, and rectum compared with goats in 2 other groups (P<0.05). Moreover, feeding LD diet moderated the decline of CaBP-D9k mRNA expression level in abomasum, jejunum and colon after lambing (P<0.05). In conclusion, reducing DCAD could up-regulate CaBP-D9k expression level in stomach, proximal intestine and colon, which was accompanied with higher plasma Ca concentration for transition goats. This result would be the possible mechanism of low DCAD enhancing blood Ca homeostasis during periparturient period to prevent hypocalcemia of transition dairy animals.
Keywords:
dietary cation-anion difference; calcium binding protein-9kDa; transition goats