| Objective: This thesis was investigated to study the anti-heat stress mechanism of ?-aminobutyric and provide theoretical basis for green, safety animal health products. By adding different concentrations of ?-aminobutyric in the diets of beef cattle, this article define the anti-heat stress function of ?-aminobutyric from some indications, such as physiological and biochemical date, production performance and so on.Then the optimum amount of ?-aminobutyric was determined in fattening period of beef cattle.Methods: The stability in the rumen fluid and release rate in the gut environment of rumen protected GABA(RP-GABA) were obtained by experiment in vitro, and the best one from those three kinds of RP-GABA was screened and employed in the subsequent test designed for anti-heat stress in beef cattle.The results are showed that:(1) The rumen constancy of RP-GABA was evaluated by in vitro test. After cultivation in the rumen fluid for 24 hours, the protection rates of I, II, III RP-GABA were 49.95%, 79.94% and 85.35%.(2) The duodenal disappearance rate of products I, II, III RP-GABA were 88.24%, 77.54% and 89.55% after treated in intestinal fluid for 8 h. Therefor, three products can provide 44.07%, 56.39%, and 76.43% true GABA to the small intestine of ruminants.In this experiment, 30 healthy jinjiang yellow cattle under summer high temperature environment were selected and randomly allotted into five groups(6 per group) in 45 days trial. The treatments were as follows:(l): Control group A: basal diet without GABA,(2): group B: basal diet with 0.85 g/d true GABA,(3): basal diet with 1.7 g/d true GABA,(4): basal diet with 2.55 g/d true GABA,(5): basal diet with 3.4 g/d true GABA. Blood samples were collected from cattle's jugular vein on the 0, 15, 30, and 45 day, serum was separated to determine related blood biochemical, physiological indexes and production performance were recorded and the nutrient digestibility was determined by collecting all dungs.The results are showed that:(1)Compared with the group A, the body temperature and respiratory rate of Group C and Group E decreased significantly on 15 th day(P<0.05); On the 30 th day, the respiratory rate of Group C decreased significantly(P<0.05) while the body temperature had not significant difference. With the degree of heat stress decreased, the temperature and the respiratory rate have no obvious difference in other test day between control group and test group.(2)In addition, the digestibility of crude protein, crude fiber, calcium and phosphorus were improved in treatment groups, whereas the difference was not significant(P> 0.05). The digestibility of crude protein and crude fiber in Group D was higher than other groups, and the digestibility of calcium and phosphorus in Group C was higher than others(P> 0.05).(3)Besides, the average weight gains in experimental groups were increased significantly, especially in groups C(1.7 g/d), its average weight gain increased by 28.30%(P<0.05). The feed conversion ratio decreased by 24.62%(P<0.05) while there were no differences on daily feed intake among all groups(P >0.05).(4)The results of blood biochemical showed that the activity of SOD in treatment groups was higher than that of control group and there is an upward trend; the MDA content of group C, D and E were significantly increased(P<0.05) on the 15 th day.(5)Meanwhile, the contents of serum thyroid hormone(T3 and T4) in treatment groups were increased; the T4 contents in treatment groups were increased significantly(P<0.05) on 15 th day; the T3 contents in group C and D were increased significantly(P<0.05) on 30 th day, and the T4 contents in group B and C were increased significantly(P<0.05) on 30 th day; the contents of serum thyroid hormone(T3 and T4)in treatment groups were significant increased on 45 th day.(6)Furthermore, the levels of the TP?ALB?GLU?ALP were increased during the experiment period. However, the content of BUN?LDH had a downward trend(P> 0.05). |
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