| This study investigated the effects of hydroxy-analogue of selenomethionine(HMSeBA)or selenium yeast(SY)on the selenium(Se)concentration in serum and milk,performance and antioxidant capacity of Holstein dairy cows in the mid-lactation period.The purpose is to provide scientific basis for the application of HMSeBA and SY in dairy cow industry.The specific research contents are as follows:Experiment 1:This study aimed to investigate the effects of HMSeBA on selenium(Se)concentration in serum and milk,performance and antioxidant capacity of dairy cows;compared to the inorganic source,sodium selenite(SS).Eight multiparous Holstein dairy cows were housed in environmental chambers.The trial was divided into 3 continuous periods: covariate period(9 d),adaptation period(28 d),and heat stress period(9 d).During the covariate and adaptation periods,all cows were housed under thermal neutral(TN)conditions.During the heat stress period,all cows were exposed to cyclical heat stress condition to establish oxdative stress model.There were 2 treatments: SS supplementation(0.3mg Se/kg DM)or HMSeBA supplementation(0.3mg Se/kg DM).All cows were fed SS during the covariate period,and dietary treatments were implemented during the adaptation and heat stress periods.The results are as follows:(1)Compared with SS control,cows fed with HMSeBA had higher total Se concentrations in serum and milk,and total Se milk: serum concentration ratio(P<0.05).(2)During the heat stress period,supplementation with HMSeBA tended to increase milk yield(P<0.1)and decreased milk fat content(P<0.05).There were no significant treatment effects on other parameters of performance(P>0.05).(3)There were no significant treatment effects on blood biochemistry(P>0.05),except for a lower alanine aminotransferase activity(P<0.05)in the HMSeBA treatment.(4)Glutathione peroxidase and superoxide dismutase activity did not differ between treatments(P>0.05),but cows supplemented with HMSeBA had higher total antioxidant capacity(P<0.05),and lower malondialdehyde,hydrogen peroxide,and nitric oxide concentrations in serum(P<0.05);compared to SS-supplemented controls.Experiment 2 : The purpose of this experiment was to explore the effects of dietary SY supplementation on the Se concentration in serum and milk,performance and antioxidant capacity of dairy cows.Thirty-six Chinese Holstein cows with similar parity,lactation day,and milk yield were randomly assigned to three groups of 12 in each group according to a completely randomized design,.The level of Se in each group was 0(control),0.5 mg/kg DM and 5 mg/kg DM.The pre-test period is 14 d and the trial period is 56 d.The results are as follows:(1)Se content in serum and milk were increased linearly and quadraticly with increase of SY supplementation(P<0.01,P<0.01).(2)Dry matter intake,milk yield and milk composition were not affected by the supplementation of SY(P>0.05),but the somatic cell counts decreased linearly with the increase level of SY(P<0.05).(3)Cholinesterase activity decreased linearly with increase level of SY(P< 0.01),but other serum biochemical indicators were not affected by the supplemtation of SY(P>0.05).(4)With the increase of SY supplementation,glutathione peroxidase activity(P< 0.01)and total antioxidant capacity(P<0.01)increased linearly and malondialdehyde content tended to increase linearly(P<0.1).Superoxide dismutase activity(P>0.05)was not affected by supplementation of SY(P>0.05).In summary,the supplementation of 0.3 mg/kg DM HMSeBA can more effectively increase the concentration of Se in serum and milk and the antioxidant capacity of dairy cows compared to the same dose of SS,and the milk yield can be improved to some extent under oxidative stress condition.The mid-lactation dairy cows had a tolerance to 5 mg/kg DM SY,and compared with 0,0.5 mg/kg DM SY,the Se concentration in milk and antioxidative capacity were significantly increased. |
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