Studies On Antioxidation Of α-Lipoic Acid In The Transition Cow

The transition or periparturient period, from 3 weeks before to 3 weeks after parturition, is a stressful time for dairy cows. During the transition period, immunosuppression commonly occurs and cows exhibit great susceptibility to a number of diseases. Most infectious diseases and metabolic disorders occur during this time. Along with a gradual decline in dry matter intake (DMI) that starts 2-3 weeks prepartum, an abrupt increase in nutrient demand with initiation of lactation results in negative energy balance and extensive mobilization of body fat. Dairy cows undergo substantial metabolic and physiological adaptations during the transition from pregnancy to lactation. An imbalance between increased production of reactive oxygen species (ROS) and the availability of antioxidant defense needed to reduce ROS accumulation during the periparturient period may expose cows to increased oxidative stress. There are nows several more recent studies to support the concept that oxidative stress is asignificant underlying factor to dysfunctional host immune and inflammatory responses that can increase the susceptibility of dairy cows during the transition period. The objective of this study was to compare changes of serum enzyme with liver function, fat metabolic parameters and lipid peroxidation in the transition cow, and investigated antioxidation of lipoic acid in the transition cow and assessed the safety of a-lipoic acid in dairy cows, so that to provide a theoretical basis for application of a-lipoic acid in the transition cow.Experiment 1. Serum concentrations of trace elements and oxidative status at different physiological stages in dairy cowsCalves (3-4 month old), replacement heifers, late-lactation cows, cows during one month before calving and after calving were selected for this study. Serum concentrations of selenium, zinc, iron, copper and manganese in dairy cows were determined. The following parameters indicative of the oxidative status were also measured in serum: glutathione peroxidase (GSH-Px) activity, superoxide dismutase (SOD) activity, catalase (CAT) activity and malondialdehyde (MDA) content. Compared with replacement heifers and mature cows, the lowest serum concentrations of trace elements in calves were found except zinc content (P<0.05 or P<0.01). There were no significant differences for serum concentrations of trace elements among replacement heifers and mature cows (P>0.05). A significantly decrease in the concentration of selenium of serum was observed at late-lactation cows and cows during one month before calving. Although serum concentrations of copper and manganese tended to be decreased for cows during one month after calving, there was no difference compared with cows during one month before calving (P>0.05). Oxidative status of serum in dairy cows was not related to age. Our results confirmed the characteristic metabolic changes associated with late pregnancy and early lactation. Activities of GSH-Px, SOD, CAT and MDA level in serum were the highest around calving. Results suggest that the concentrations of trace elements and oxicative status of serum in calves were the lowest, and there were indicatoins for an imblance in those parameters during one month before calving and early lactation.Exiperient 2. Changes in fat metobilism, liver function and lipid peroxidation of the transition cowThirty Holstein dairy cows at 30d before calving were selected for this study. Serum samples were collected at 30,20,10,5d before calving, Od calving and at 5,10,15,20d after calving. Fat metoblism (concentrations of GT, Chol, NEFA, HDL and LDL), liver enzyme activities (AKP, LDH, ALT and AST activities), and lipid peroxidation (GSH-Px, SOD and CAT activities, MDA content) in serum were measured. The result show that:①Concentrations of serum TG had a declining trend from 30d prepartum and decresed sharply on the day of calving. Concentration of Chol had a declining trend before calving and then increasing after calving. NEFA concentrations increased at calving, reaching peak level on day 5 postcalving and started to decrease thereafter. Concentrations of serum HDL and LDL decreased slightly in the prepartum period and increased gradually postcalving.②LDH and AST activities were the higest at day 5 before calving and the day of calving, respectively. ALT and AKP activities did not differ signifiantly at any stage.③) CAT and GSH-Px activities showed a declining trend in the prepartum period and increased at the day of calving followed by a decrease. SOD activity had increasing trend from day -30 to 0 and started to decrease thereafter.④MDA content increased from day 5 precalving and decreased from day 5 postcalving. In conclusion, dairy cows seem to undergo extensive mobilization of body fat and an imbalance in the oxidative status in the transition period, and liver function is impaired because of hepatic lipidosis.Experiment 3. Effect ofα-lipoic acid on oxidative status in the transition cowForty-eight Holstein dairy cows at 20d before calving were divided into four groups. GroupⅠwas control. GroupⅡtoⅣwere fed withα-lipoic acid (3,5 or 8g/d) for 50 days, respectively. Serum glutathione peroxidase (GSH-Px) activity, superoxide dismutase (SOD) activity, catalase (CAT) activity and malondialdehyde (MDA) content were measured. Serum GSH-Px, SOD activities were significantly higher between days 20 or 40 to days 50 in groupⅢandⅣthan in control group, respectively (P<0.05 or P<0.01). Serum CAT activities were significantly higher on days 30 in groupⅡand days 30,40 and 50 in groupⅢandⅣwhen compared with control group (P<0.05). Serum MDA concentrations were markedly reduced on days 40 in groupⅢand days 50 in groupⅣwhen compared with control group (P<0.05). Our results suggest thatα-lipoic acid supplementation can improve antioxidant capacity in the transition cow.Experiment 4. Effect ofα-lipoic acid on fat metabolic parameters and liver enzyme activities in the transition cowForty-eight Holstein dairy cows at 20d before calving were divided into four groups. GroupⅠwas control. GroupⅡtoⅣwere fed withα-lipoic acid (3,5 or 8g/d) for 50 days, respectively. Blood samples were collected before the beginning of supplementation and at intervals of 10 days after supplementation. The following parameters indicative of fat metabolism and liver enzyme activities were measured in serum:triglyceride (TG), cholesterol (Chol), nonesterified fatty acid (NEFA), high-density lipoprotein (HDL), low-density lipoprotein (LDL) and alkaline phosphatase (AKP),γ-glutamyl transferase (γ-GT), lactate dehydrogenase (LDH), alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Serum fat metabolic parameters were decreased by a-lipoic acid treatment, but only serum NEFA concentrations were significantly changed on days 30 in groupⅣwhen compared with control group (P<0.05). Serum AST activities were significantly lower on days 30 in groupⅡ,ⅢandⅣthan in control group (P<0.05 or P<0.01). There were no significant differences in other parameters between the treated groups and the control. Our results suggest thatα-lipoic acid supplementation can improve fat metabolism and protect liver function in the transition cow.Experiment 5. Safety evaluation ofα-lipoic acid in dairy cowsIn order to test the toxicity of a-lipoic acid (ALA), in an acute toxicity study, three Holstein dairy cows were dosed at 50g ALA and another three Holstein dairy cows were dosed at 100g ALA, respectively. In an subchronic study, cows were subjected to oral adminstration of 10g ALA for 15 days. The result show that:①Administration of ALA to dairy cows at doses of 50g by oral gavage was without adverse effects. No clinical signs of toxicity were apparent within one week of dosing and biochemical values were normal.②In the dairy cows dosed at 100g ALA, clincal signs of toxicity were apparent within 3 h of dosing and died during the 7 h post-dosing observation period.③Adminstration of 10g ALA for 15 days to dairy cows did not adverse effects. Serum SOD, CAT activities were significantly higher from 9d in treatment group than in control group, respectively (P<0.05). MDA concentrations were markedly reduced on days 12 in treatment group when compared with control group (P<0.05). There were no significant differences between the treated animals and control animals to clincal chemistry parameters. Results suggest that the no-observated adverse effect level (NOAEL) is considered to be≤50g (77～100mg/kg bw) and absolute lethal dose (LD100) is considered to be 100g (154～200mg/kg bw) in Holstein dairy cows. However, ALA dose as a biological antioxidant in dairy cows is below 10g/d (15～20mg/kg bw/d).