| This experiment was conducted with 15 cows in early lactation, 15 cows in midlactation to study the effect of dietary cation-anion balance (DCAB) on production performance, blood physiololgical and biochemical parameters of Chinese Holstein heat-stressed lactating cows in different lactating period as to determine the best level of DCAB in different lactating period and to explain the mechanism of its effects preliminatily.15 cows in early lactation and 15 cows in midlactation were selected respectively in two replictated 3x3 Latin squar design, and were assigned randomly into 3 groups each with 5 replicates to study the effects of dietary cation-anion balance(DCAB) on performance, blood biochemical parameters. Treatments involved the control group A (basal diet: with a DCAB of 83 meq/kg DM), B (with a DCAB of 275 meq/kg DM), C (with a DCAB of 325 meq/kg DM) in early lactation; the control group A'(with a DCAB of 77 meq/kg DM) , B'(with a DCAB of 175meq/kgDM) , C'(with a DCAB of 325 meq/kg DM) in midlactation. The main results showed as follows: (1) DCAB remarkably influenced the blood gas parameters. The blood pH of B and C groups increased significantly compared with the control group (PO.05) , the content of B group was extremely significandt (PO.01) in early lactation; the influnces of DCAB on blool pH of B' and C' groups were not significant compared with the control group. Increased DCABcaused a increase in HCO3" and total CO2 (Tco2) concentrations in blood, furthermore the HCCV and Tco2 concentrations of the B group in early lactation was significant compared with the control group, and it had no significant difference with the other groups. Increased DCAB reduced partial pressure of carbon dioxide (Pco2) in blood significantly (P<0.05) . Partial pressure of xoygen (Po2) and xoygen saturation^ 50 M ?53 ftDCAB(SATo2) concentrations in blood increased with increased DCAB. Po2 and SATo2 in blood of B group and C group in early lactation increased 3.26% (PO.05) and 0.55%(PO.05), 0 and 0.13% respectively compared with the control group; the content of P2 and SATO2 in blood of B' group and C' group in midlactation increased 5% (PO.05) and2.46% (PO.05 ), 4.2% (PO.05) and 1.65% (P>0.05) respectively compared with the control group. Increased DCAB caused a increase in actual base excess (ABE) and standatd bicaronate (SBC) in blood. (2) Lutropin (LHX 3,5,3'-triiodethyronine (T3X thyroxine (T4), hydrocortisone (COR) in blood serum were unaffected by diet. Blood serum estradiol (E2) concetration increased linearly with DCAB, the content of B group and C group in early lactation increased 1.49 times (PO.01) and 2.14 times (PO.01) respectively compared with the control group; the content of B' group and C' group in midlactation increased 24.29 (P>0.05 ) and 39.32% (PX).05). Increased DCAB decreased creatine kinase ( CK) in serum significantly, compared with the control group the content of B group and C group in early lactation reduced 29.1% (PO.01) and 25.2% (PO.01) respectively; the content of B' group and C' group in midlactation reduced 13.14%(P>0.05 ) and 9.01 % ( P>0.05), but they were of no significant difference. Increased DCAB had no significant effects on alkaline phosphatase (ALP) and glutamic-pyruvic transaminase enzyme (GTP) in serum. Urea nitrogen of blood serum was affected by diet, increased DCAB reduced urea nitrogen . The content of urea nitrogen of B' group in early lactation was significant compared with the control group, but it had no significant difference with the other groups. Blood sugar, serum protein, serum albumin increased a little, but there was no significant difference among them. (3) Increased DCAB affected production performance significantly. The mild yield and 4% fat corrected milk yield of Band C group in early lactation increased 10% (PO.05) and 10.1% (PO.05), 3.9% (P>0.05) and 3.0% (P>0.05) compared with the control group respectively; The mild yield and the 4% fat corrected mild yield of B' group and C' group in midlactation increased 6.6% (P>0.05) and...
|
PDF Full Text Request