| The dairy industry is one of the important development industry in our country, but also is an important strategic industries to improve the diet, the level of development of the dairy industry is not only an important symbol of a national agricultural development level, but also an important indicator of the national people’s living standards. Due to the lack of high-quality roughage, concentrated feed is often extensive used to meet the needs of the animal body’s nutrition, but high concentrate diet causes rumen abnormal fermentation, severe cases may occurrence the Acute ruminal acidosis (ARA), chronic cases may occurrence the Subacute ruminal acidosis (SARA), especially the latter, due to the high incidence and subclinical, may cause enormous economic losses to production.Histamine is a kind of self-body active substances and trace amounts of histamine is not harmful to body under normal physiological conditions. When the rumen occurs abnormal fermentation will produce large amounts of histamine which is degraded in the liver, when high levels of histamine in the peripheral blood, causing a variety of diseases, such as mastitis, laminitis and so on, these diseases will reduce the production capacity of the cows. In addition, most of the dairy farms use the dietary levels which concentrate-roughage ration is between 4:6 and 6:4 in our country, so research pH changes and the formation of histamine in the rumen and histamine metabolism in the liver have great academic values and practical value under the dietary forage to concentrate-roughage ratio of 4:6 and 6:4.Test I Setting up a method for determination of histamine concentration in the rumen fluid and blood. Histamine was determined by RP-HPLC and UV detector in this test, samples were extracted by 0.5mol·L-1 hydrochloric acid, then pre-column derivatization with dansyl chloride, the chromatogram column was Agilent ZORBAX 80A Extend-C18 (4.6 mm×250 mm,5μm), mobile phase A was acetonitrile and mobile phase B was 0.1% ammonium acetate, using gradient elution, mobile phase ratio was A:B=80:20, rate was 1.0ml/min, the injection volume was 20μL, Column temperature was 30℃, detection wavelength was 254nm, resulted standard curve:y=0.0008x+0.0568, R2= 0.9997, linear range:0.1μmol·L-1 to 100μmol·L-1, detection limit:0.015μmol·L-1, recovery rate:95.45%, therefore, the success of setting up a method for determination of histamine concentration in the rumen fluid and blood.Test Ⅱ Effects of dietary forage ratio on the pH values and histamine generated in the rumen.4 dairy goats which were fitted with rumen fistula used for crossover experiment, fed dietary forage to concentrate-roughage ratio of 4:6 and 6:4 respectively by two periods which has equal energy and nitrogen. Three weeks for one period, then on 21 days rumen fluid samples were respectively collected before feeding and after feeding on 2, 4,6 and 8 h. The results showed that:(1) The rumen fluid pH of dairy goats which were fed dietary forage to concentrate ratio of 4:6 was lower than that of the ratio of 4:6, the decline rate and magnitude of the pH value which were fed the high-concentrate greater than the low-concentrate diet. (2) The rumen fluid pH values of dairy goats which were fed forage to concentrate-roughage ratio of 6:4 below 6 for six hours, suggested that the dairy goats may have occurred SARA. (3) The rumen fluid histamine content of dairy goats which were fed forage to concentrate ratio of 6:4 was higher than that of the ratio of 4:6(P<0.01), suggestive of histamine may promote the occurrence and development of SARA.Test Ⅲ Effects of dietary forage ratio on histamine metabolism in liver.4 dairy goats which were fitted with portal vein catheterization and hepatic vein catheterization used for experiment, feeding cycles and the sampling time the same as the second experiment. The results showed that:(1) Histamine concentrations of venous blood tended to increase which was fed by the high concentrate diet, it reveals high concentrate diet increased the content of histamine in the blood. (2) The histamine concentration in the portal vein was higher than the concentration of histamine in the hepatic vein (P<0.05), this showed that the liver had the ability to clear the histamine. (3) The liver clearance rate of dairy goats which was fed the high concentrate diet was higher than that of fed low concentrate diet, but the difference was not significant.Test IV Effects of dietary forage ratio on the expression of histamine receptor mRNA in liver.6 dairy goats used for crossover trial, feeding cycles and the sampling time the same as the second experiment. The results showed that:(1) Histamine receptor H1 may play a dominant role of histamine metabolism in the liver of dairy goats. (2) The expression rate of histamine receptor H1 under fed the high concentrate diet was higher than that of low concentrate diet, but the difference was not significant.In summary, feeding high concentrate diets may lead to SARA occurred on dairy goats, histamine content in the rumen was significantly increased, histamine concentration in the blood and the expression rate of the histamine receptor H1 have the tendency of increase, the liver clearance rate of dairy goats was not significantly increased in our current dietary levels. The elevated histamine concentration may play an important role to promote the occurrence and development of SARA. |
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