Effects Of Exogenous Metallothionein On Several Reproductive Hormones Regulation And Mechanism Of Dairy Cattle

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-â… (IGF-â… )concentration in group B increased significantly compared with group A(P<0.05);T₃ and IGF-â… concentration 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-â… concentration 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-â… in serum of dairy cattle,and presented time-and dose-dependent fashion.