The Effects Of Dietary Cation-Anion Balance On Ruminal Metabolism And Lactating Performance Of Dairy Cows During Heat Stress

The objective of the study was to evaluate the effects of DCAB [Dietary Cation-Anion Balance; DCAB=(Na++K++0.15Mg2++0.15Ca2+)–(Cl-+0.6S2-+0.5P1.8-); mEq/100g DM] on the metabolic parameters and performance of cows during different physiological period through separately supplementing cationic salts in the diets of cows during early lactating period and midanaphase period.The main proposal was to search the best level of DCAB corespandence with different productive condition.and the dissertation was described in the following 4 sections.Experiment 1: The objectives of this part was to determine the effects of DCAB on the rumen fermentation. The in vitro culture were conducted using substrates, by level 20, 25, 30, 40mEq/100gDM of DCAB in culture medium, respectively. The results indicated that, Increasing DCAB could increased pH and osmotic pressure and improved cation-cnion balance, could increased bacterial protein production and decreased protozoa protein production as well. But could not changed fermentation pattern of rumen. Compared to control group, no significant difference was observed in ruminal concentration of VFA(P>0.05). Aerogenic accumulation was ascendant and experimental groups were significantly higher than control group as the addition of DCAB increasing. (P<0.01).Experiment 2: Increasing DCAB on fiber enzyme and cellulose degradation were studied in this part, and the level of DCAB in culture media were the same as the experiment one. Molecular biology techniques were used to study the effects of DCAB on bacteroide succinogenes, ruminococcus albus and ruminococcus flavefaciens. The results showed that, increasing DCAB could increased the activity of carboxymethyl cellulose significantly, filter paper cellulose enzyme and xylanase emzyme. And the activity of filter paper cellulose enzyme and carboxymethyl cellulose were highest in C group. It was also observed that, xylanase activity was highest in D group. Increasing DCAB could significantly increased the populations of bacteroide succinogenes and ruminococcus albus and ruminococcus flavefaciens (P<0.05). The population of bacteroide succinogenes of C group was extremely higher than that of the control group (P<0.01). The population of ruminococcus albus of C group was higher than the control group (P<0.05). Group D had the higest population of ruminococcus flavefacien(sP<0.05). Increased cellulose degradability was accompanied by increasing DCAB within certain limits.Experiment 3: Eeffets of dietary cation-naion balnaee on blood acid-base balance, nitrogen balance and production performance of early lactating dairy cows was studied in this part.The experiment was conduced with 12 cows in early lactating cows to study the effect of dietary eation-anion balance (DCAB) on production performance of Chinese Holstein cows as to determine the best levels of DCAB. They were divided four groups randomly: Group A (DCAB with 20mEq/100gDM), Group B (25mEq/100gDM), Group C (30mEq/100gDM, Group D (40mEq/100gDM). The duration of experiment was 21 days. The result indicated as follow: Increasing DCAB swelled obviously blood cushion and transport O2 ability of dairy cows. Blood pH and blood HCO3- increased predominantly via increased DCAB(P<0.05).The group B has significant effect on TCO2 and blood base excess compare with the group A(P<0.05).Increasing DCAB did not effect distinctly on the other blood gas items(P>0.05).Increasing DCAB swelled obviously glucose blood and urea nitrogen of dairy cows within a bounds. The increased DCAB affected production performance as well. The milk yield of group B,C increased significantly with7.12%,5.58% compared to A(P<0.05), But it had no significant effect on protein of milk, fat of milk and total solid(P > 0.05). The production performance, nitrogen balance and ADF, NDF digestibility were the best when DCAB was 25mEkq/100g DM .Experiment 4: Eeffets of dietary cation-naion balnaee on blood acid-base balance, nitrogen balance and production performance of midanaphase dairy cows was studied in this paper.The experiment was conduced with 12 cows in metaphase cows to study the effect of dietary eation-anion balance (DCAB) and to determine the best levels of DCAB. The level of DCAB in culture media were the same as the experiment three. The result indicated as follow: Increasing DCAB swelled obviously blood cushion and transport O2 ability of dairy cows. Blood pH and blood HCO3- increased predominantly via increased DCAB(P<0.05). The group C has significant effect on TCO2 and blood base excess compare with the group A(P<0.01).Increasing DCAB did not effect distinctly on the other blood gas items(P>0.05).The increased DCAB could affected production performance but it had no significant effect.The production performance, nitrogen balance, ADF and NDF digestibility were the best when DCAB was approximately in 30 mEkq/g DM mEq/100g DM.