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To explore the effect of exogenous metallothionein（MT） on several reproductive hormones regulation and mechanism of dairy cattle,an experiment with 6×4 randomized complete block design was conducted with 24 lactating cows,treatments A,B,C and D were supplemented with 0,4.0,8.0 and 12.0 mg Zn-MT·capita-1,respectively,by intravenous injection.The results showed follows:serum prolactin（PRL） in groups B,C and D,estradiol（C） levels in groups B and C were significantly higher than those in control group（group A）（P<0.05） on the 15th day after injection.Simultaneity,serum follicle stimulating hormone（FSH） in group B was significantly higher than groups A,C and D（P<0.05）,but groups C and D lower than that in group A,and the difference was not significant（P>0.05）.At the same time,butterfat percentage increased 0.42 percent in group D compared with the first day（P<0.05）.Serum FSH in group B was significantly higher than groups A,C and D（P<0.05） on the 30th day after injection,but groups C and D less than group A（P>0.05）.However,the serum insulin（INS）,progesterone（Prog）, triiodothyronine（T3） and insulin-like growth factor-Ⅰ（IGF-Ⅰ）concentration in group B increased significantly compared with group A（P<0.05）;T3 and IGF-Ⅰconcentration was significantly higher than group A（P<0.05）;MT content in milk in groups C and D increased 1.26 and 0.52 times compared with group A（P<0.05）;serum E2 in group D were significantly higher than those in group A（P<0.05）;serum Prog and milk fat percentage increased significantly compared with the first day（P<0.05）.Serum Prog in group B was significantly higher than the first day and group A（P<0.05）,and T3 concentration in group B was significantly higher than group A on the 45th day after injection（P<0.05）.Furthermore,T3,IGF-Ⅰconcentration and milk fat percentages in group C increased significantly compared with group A（P<0.05）;E2 levels in group D increased significantly compared with group A（P<0.05）;Serum Prog level and butterfat percentage in group D increased significantly compared with the first day（P<0.05）.In addition,milk protein rate in groups B,C and D increased significantly compared with the first day（P<0.05）;total fat correct milk yield of groups B,C and D were 3351.6,3369.6 and 3377.7 kg,respectively,increased 223.1,251.1 and 259.2 kg compared with group A（3118.5 kg,P<0.05）.In conclusion,exogenous bovine MT with 4.0 mg·capita-1 group had the best effect of the several reproductive hormones regulation in 1-30 days after injection,but 8 mg and 12 mg·capita-1 group in 16-45 days after injection.All of these suggested that exogenous bovine MT should be a physiologically active substance to control some of the reproductive hormone secretion and release to improve milk yield and its quality,and maintain high level of the PRL,E2,T3,INS and IGF-Ⅰin serum of dairy cattle,and presented time-and dose-dependent fashion.
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