Effect of anionic Supplements and dietary anion-cation balance of dry cows on invitro Ruminal Fermentation properties

Differences between specific anions and cations have a greater contribution to the physiological performance of animals than their individual effect. The difference between cations and anions in milliequivalents of the diet is referred to as the cation-anion difference or the anion-cation balance (Razzaghi 2009). DCAD manipulation by altering blood buffering capacity, improves milk production in dairy cow (Sanchez 2003). Feeding diets with low DCAD during the Prepartum period is a practical nutritional strategy to increase blood calcium and produce more milk Postpartum. Diets containing low DCAD increased the concentration of hydrogen ions in the blood, resulting in mild acidosis and increased calcium absorption (Moore et al 2000). Decreasing DCAD by feeding anionic salts lowers blood pH and increases the binding of parathyroid hormone to the parathyroid hormone receptor on bone, intestinal, and kidney cells (Goff 2004). However, feeding anionic salts reduces prenatal feed intake due to its bitterness; but it improves postpartum calcium metabolism (Golfert et al 2010). One way to activate postpartum calcium homeostasis is to use DCAD-negative diets in the Prepartum period. Nutrition High-anion diets, commonly known as "anion-salt diets," have been used to prevent milk fever for the past 40 years. One possible reason is that dietary metabolic acidosis increases the tissue response to parathyroid hormone. Therefore, the aim of this experiment was to investigate the effect of anion source type and anion and cation balance on rumen fermentation parameters in dry cows invitro.

This study was done at the Research Farm and laboratories of the Department of Animal Sciences, Faculty of Agriculture, in University of Birjand, using the ruminal fluid of two dry Holstein cows with ruminal fistula. In order to investigate the effect of source and dietary anion-cation difference (DCAD) of dry cow's diet on gas production parameters, ammonia nitrogen concentration(N-NH3), rumen pH and dry matter digestibility in in vitro condition. Basal diet was prepared based on the requirements of dry cows. In the next step, concentrations of calcium, sodium, potassium, magnesium, chlorine, phosphorus and sulfur in the basal diet were determined by atomic absorption spectroscopy and the DCAD of the basal diet was calculated. After this, the anionic salts of calcium sulfate hemihydrates, sulfuric acid, phosphoric acid and monobasic ammonium phosphate were added as a percentage of the diet in solution form to the base diet with a sampler to reach the desired anion-cation balance. The factorial experiment conducted in a completely randomized design with 12 treatments and 15 replications. Anionic salts of calcium sulfate hemihydrates, sulfuric acid, phosphoric acid, ammonium phosphate monobasic and different DCAD levels (-56.6, -11.33 and -17.0 meq/100gDM) were used. Each treatment was including a DCAD level and a sulfur and phosphorus source that balanced according to each element ratio in table of requirements. In the next step, the gas from fermentation was measured based on the modified method of Bloomel et al. (1997). The produced gas pressure was recorded at times of 2, 4, 6, 8, 12, 24, 36, 48, 72, 96 and 120 hours from the beginning of incubation. The data were plotted against time and analyzed using the exponential Schofield model (P = v (1-exp (-k (t)))) in the NLIN procedure of SAS software. At times of 12, 24, 48 and 72 hours after incubation, three vials of each replicate were removed from incubator and after recording gas production, immediately after opening the cap, the pH of each vial was measured Using a digital pH meter (Metrohm 727 pH lab). In order to determine the concentration of ammonia nitrogen after centrifugation of the contents of each vial, 5 ml of clear supernatant was removed from it and combined with 333 μl of 3 N hydrochloric acid and then stored at -20 ° C. Phenol and hypochlorite reagents were used to measure ammonia nitrogen and the adsorption was read by ELISA at 650 nm (Bradrick and Kang, 1980). In order to determine the rumen digestibility of the dry matter, the residues obtained from each vial were oven dried in 60 ° C for 48 hours.

The results showed that the effects of experimental treatments on gas production parameters, rumen pH and ammonia nitrogen concentration were significantly different at different incubation times (p <0.05). The highest gas production potential per fermentable substrate is related to Treatment containing DCAD level of -5.66, which is supplied from two sources of phosphoric acid and sulfuric acid. As expected, the total gas production at 120 hours of incubation and also gas production at t0.5 is related to this treatment. The fermentation rate and time to reach half of the gas production potential in this treatment is average. Therefore, it can be concluded that this treatment has been able to provide suitable ruminal buffering conditions for microorganisms due to good results in DM digestibility too. The highest area below the pH curve of ruminal fluid was related to treatment with DCAD of -5.66, which was obtained from ammonium phosphate and sulfuric acid sources. The lowest level below the pH curve of ruminal fluid is related to the treatment containing DCAD -11.33, which is provided from sources of phosphoric acid and sulfuric acid. The highest ammonia nitrogen production is related to the treatment containing the anion-cation balance of 170 with two sources of sulfuric acid and phosphoric acid. Ammonia nitrogen is strongly influenced by the breakdown of crude dietary protein by microorganisms and the breakdown of the microbial population due to nitrogen recycling under adverse conditions. On the other hand, because the dry matter digestibility has increased at this time and in this treatment, this increase is probably related to the breakdown of feed crude protein due to improved fermentation conditions. In general, the use of phosphoric acid and sulfuric acid sources with the anion-cation balance of -5.66 meq/100gDM improved the gas production parameters, the rumen pH curve under area, and the ammonia nitrogen concentration.