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Wu Lizhuan,Chen Haiyan,Zhang Bin,Li Lili,Xiao Bingnan,Chen Yuguang,Xiao Dingfu,Luo Jiajie,Wu Zongming |
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Abstract:To approach the effects of exogenous metallothionein (Zn-MT) on endocrine hubs of dairy cattles on the low-grade thermal stress, an experiment was conducted with 24 lactating cows, who were randomly allocated to groups A, B, C and D, and supplemented with 0, 6.0, 12.0 and 16.0mg Zn-MT•capita-1, respectively, by intravenous injection. The results showed that: The corrected milk yields in groups B, C and D were higher than those in groups A (P<0.05or P<0.01), the fat percentages of milk was improved significantly (P<0.05). The secretory capacity of INS in control group was lower than in experimental groups, especially in group B in 30d(P<0.01); the secretory capacity of IGF-Ⅰand T3 in groups B, C and D were higher than those in groups A (P<0.05or P<0.01), and in 45d, the same capacity in group C was the highest among all these numbers. The FSH in groups B and C constantly maintained low level, but the range of variation of FSH in group A was 4 times as same as in group C; The secretory capacity of Prog and E2 in experimental groups were higher than those of group A in anaphase (30~45d)(P<0.05); and the PRL in groups B, C and D were higher significantly than those in groups A (P<0.01), and the effect was faint in anaphase (P>0.05). Exogenous Zn-MT had the best effects on the thermoresistance of diary cattle 12.0mg•capita-1 by intravenous injection every 30~45 days. On one hand, the speed of catabolism and quantity of heat production in bodies were reduced by Zn-MT through adjusting secretory volume of endocrine hormone which is related to energy metabolism, on the other hand, to approach the healthful effects of thermoresistance, the gonadal hormones were controlled amplitude of variation, and on the same time, the secretory volume of PRL was improved by Zn-MT, which resulted in physiological status which was varied on balance for diary cattle. |