| The objective of the study was to evaluate the effects of DCAD [Dietary Cation-Anion Difference; (Na++K+)-(Cl-+S2-) mEq/kg DM] on the metabolic parameters and performance of cows during different physiological period through separately supplementing anionic salts and cationic salts in the diets of cows during dry period and early lactating period.The first part was to ascertain the effects of negative DCAD on the metabolic parameters, health status and postpartum milk performance. Sixteen healthy Chinese Holstein cows in dry period were randomly allocated to two diets (n=8) with DCAD values separately of +138.40mEq/kg DM and -240.79mEq/kg DM. The diets were feed till the cows'parturition at the 21th day before parturition. The results showed that: (1) Decreased DCAD could effectively to reduce hypocalcemia of dairy cows. Decreasing DCAD improved clearly dairy cows'serum P (P=0.0004), decreased clearly parathyroid hormone (P=0.0191) before parturition 7 days; improved obviously serum Mg (P=0.0118) and serum P (P=0.0262), and still clearly made parathyroid hormone (P=0.0101) lower than control group at the parturition day; still clearly made serum P (P=0.0100) higher than control group, and decreased predominantly alkaline phosphatase (P=0.0350) after parturition 7 days. (2) Decreasing DCAD reduced the incidence of disease, and was benefit to dairy cows'health. (3) Compared with the control group, it were both increased for trial group dairy cows'4% fat corrected milk of the 2nd and 3rd (P=0.0388 vs. P=0.0250), and decreasing DCAD could decreased somatic cell counts and improve milk composition, such as fat rate, protein rate, lactose rate and total solid, and so on (P>0.05). Adjusting DCAD was -240.79mEq/kg DM to dry cows could effectively meliorate dairy cows'health and increase milk performance. The second part was to ascertain the effects of positive DCAD on heat-stress (THI>72) early-lactating dairy cows'blood acid-base balance, physiological & biochemical items and milk performance. Thirty-six early-lactating Chinese Holstein dairy cows were randomly allocated to three diets (n=12) with DCAD values separately of +130.49 (Control), +251.54 (Treatmentâ… ) and +383.87 (Treatmentâ…¡). (1) Increasing DCAD swelled obviously blood cushion and transport O2 ability of dairy cows. Blood pH (P=0.0408) and blood base excess (P=0.0447) increased predominantly via increased DCAD. Increasing DCAD did not effect distinctly on the other blood gas items (P>0.05). (2) Increasing DCAD could effectively reduce heat-stress of dairy cows. Increasing DCAD had significantly reduced blood urea nitrogen (P=0.0013) and creatine kinase (P=0.0202), increased total protein (P<.0001) and albumin (P<.0001) in serum of dairy cows, but blood lactose (P=0.0644) increased linearly with DCAD increased. (3) Increasing aptly DCAD affected milk production significantly. 4% fat-corrected milk (P=0.0362) ofâ… group andâ…¡group increased 11.0% and 5.1% respectively compare with the control group. Adjusting DCAD was +251.54mEq/kg DM to early-lactating dairy cows could reduce dairy cows'heat stress, and improve the milk performance. |
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