Effects Of Dietary Fat And Energy Density On Oxidative Stress And Lactation Performance In Dairy Cows, In The Absence Or Presence Of Antioxidant

Dietary fat is susceptible to oxidation during any stage of processing, storage and feeding. Lipid oxidation also often occurs in animal body when the production of free radicals exceeds the capacity of antioxidant system. This study contained three parts including five experiments. In the first part, the stability of different ingredients rich in fat was evaluated, in the absence or presence of antioxidant (AOX) (Expt.1). To evaluate the potential oxidation of lipid in dairy cows, the lipid metabolism character and its correlation to anti-oxidative status was investigated in Chinese Holstein cows (Expt.2). Then, in the second part, two types of fatty acids that differ in stability and saturated degree were selected to evaluate their effects on performance and anti-oxidative status in high lactating cows, in the absence or presence of antioxidant (AOX) (Expt.3). An in vitro gas test trial was carried out to investigate the effect of different rumen inert fatty acids with a dietary antioxidant on rumen fermentation, anti-oxidative status and microflora (Expt.4). In the last part, two pre-partum diets with different energy density were formulated to study the effect of energy level on lipid metabolism and anti-oxidative status, in the absence or presence of AOX (Expt. 5).Part one:Evaluation of stability in the diets rich in fat and lipid oxidation in dairy cows (Expt.1 and 2).In Expt.1, Ingredients that rich in fat were selected and mixed with 0 or 500 ppm antioxidant (AOX). Peroxide values (POV) in the room temperature were determined by active oxygen method (AOM), and induction time was determined by ML OXIPRESTM at 100℃. The POV value in the whole seed was lower, ranging from 0.67meq/kg in extruded soybean to 2.27meq/kg in DDGS. Addition of AOX decreased the POV by 32 to 68% based on the ingredients. However, the POV was higher in unsaturated calcium salt of long chain fatty acids, compared with saturated fatty acid (33.13 vs 4.53 meq/kg), while the induction time showed the opposite results. The AOX could improve the stability of unsaturated calcium salt of long chain fatty acids by 3 times, but only 50% improvement was found in saturated fatty acid. The stability of cotton seed with AOX was 7-8 times of that without AOX. It is indicated that AOX could improve the stability of the diets, especially when polyunsaturated fatty acids were included in the diets.The objective of Expt.2 was to evaluate the potential oxidation of lipid in dairy cows. The lipid metabolism and its correlation to oxidative status were investigated in Chinese Holstein cows during transition period. Ten cows with similar parity, expected calving date, and body condition score were selected and blood samples collected weekly by coccygeal vein from-3 to 3 weeks relative to calving. Another ten cows in late-lactating were selected as control. The concentration of plasma glucose was higher in transition cows, compared to late-lactating cows. After calving, plasma glucose decreased to a lower level, compared to that at calving and prepartum (2.58 at 1 week postpartum vs 3.83 mmol/L at calving). The nonesterified fatty acid (NEFA) peaked 1 week postpartum, significantly higher than that in prepartum and control cows. Similar to the control, plasma triglyceride postpartum was lower than that prepartum. Activity of superoxide dismutase (SOD) in transition cows was lower than late-lactating cows, especially 0 and 1 week relative to calving. Meanwhile, malondialchehyche (MDA) reached to the highest level 1 week postpartum, contrasting with activity of antisuperoxide anion free radical (ASAFR), which decreased to the lowest level. Concentration of NEFA was related to most of anti-oxidative parameters (R= 0.74,-0.61 and-0.56 for MDA, ASAFR and TAOC, respectively). In summary, transition cows are susceptible to oxidative stress, indicated by lower SOD and ASAFR activity after calving. The increased requirement to glucose during the initial step of lactation cows will make cows mobilize adipose tissues. The oxidative status may have a close relationship with lipid metabolism.Part two:Effect of diets supplemented with fatty acids of different degrees of saturation, in the absence or presence of AOX, on lactation performance and rumen fermentation in dairy cows (Expt.3 and 4).The objective of Expt.3 was to evaluate the effect of diets supplemented with fatty acids of different degrees of saturation, in the absence or presence of AOX, on lactation performance of dairy cow. Calcium salt of long-chain fatty acids was supplemented as a source of lower saturation fatty acid (LS,53.9% SFA), and palmitic acid was supplemented as the higher saturation fatty acid source (HS,88.6% SFA). The AOX was added at 0.025% in the ration. Neither fatty acid type nor AOX supplementation showed significant effect on dry matter intake (DMI) during the study. Compared with those in HS, yield of milk and 4% FCM were lower in the LS-fed cows. Milk fat and milk protein concentrations were not affected by fatty acid type or AOX supplementation. Adding AOX increased the yield of milk and 4% FCM in the LS-fed cows, but did not affect those fed HS. Plasma SOD activity was significantly lower, plasma glucose tended to be lower, and plasma MD A was higher in the LS-fed animals, compared with those fed HS. Addition of AOX decreased both plasma NEFA and H2O2 contents and increased TAOC activity across the fatty acid types. Composition of C12:0, C18:0, cis-9 C18:1, trans-11 C18:1, C18:2, C20:5 and C22:6 in the erythrocyte membrane was higher, while C14:0, C16:0 and C16:1 was lower for cows fed diets supplemented with LS, compared with those with HS. Addition of AOX increased C14:0, C14:1 and C16:1 and decreased C18:0, cis-9 C18:1, C20:5 and C22:6-composition in the erythrocyte membrane. Cows fed LS had higher cis-9 C18:1 and trans-10, cis-12 C18:2 in milk at the expense of C18:0, whereas AOX addition increased milk cis-9 C18:1 at the expense of milk C12:0, C16:0, and trans-10, cis-12 C18:2. It is inferred that dietary inclusion of unsaturated fatty acids resulted in inferior lactation performance. Whereas, these negative effects may be partially alleviated by the addition of antioxidant.Experiment 4 was carried out to evaluate the effect of LS and HS supplementation on rumen fermentation in vitro, in the absence or presence of AOX. The experiment was carried out in a 2×2 factorial design, with fatty acids type as one factor and AOX as another one. Fermentation patterns and anti-oxidative status were not affected by different fatty acids supplementation. Supplementation of LS significantly increased the populations of protozoa relative to total bacterial 16S rDNA, but showed negative effect on fibrobacter succinogenes. Addition of AOX significantly increased gas production at 24h incubation. Molar proportion of propionate tended to increase at the expense of acetate due to AOX addition. AOX tended to decrease MDA value and increase SOD activity. An interaction between AOX and fat type was observed on ruminococcus flavefaciens and ruminococcus albus. Inclusion of AOX increased these two bacteria in LS group, but not in HS. It is concluded that unsaturated fatty acids inclusion in the diets may result in inferior effect on cellulolytic bacteria in the rumen, while these negative effects may be partially alleviated by the addition of antioxidant.Part three:Effect of energy density prepartum on performance and anti-oxidative status in transition cows, in the absence or presence of antioxidant (Expt.5)In Expt.5, a 2 x 2 factorial design trial was conducted to evaluate the effect of dietary antioxidant and energy density on performance and anti-oxidative status in transition cows. Forty cows were randomly allocated to 4 dietary treatments. High or low energy density diets prepartum (1.43 or 1.28 Mcal NEL/kg DM, respectively) were formulated with or without AOX (0 or 5 g/d per cow). These diets were fed to cows for 21 days pre-partum. During the post-partum period, all cows were fed the same lactation diets, and AOX treatment followed as for the pre-partum period. Feeding a high energy diet depressed the DMI, milk yield, and 4% FCM of cows. However, AOX inclusion in the diet improved the milk and 4% FCM yields. There was an interaction of energy density by AOX on milk protein, milk fat and total solids contents. Feeding a high energy diet pre-partum significantly increased plasma glucose andβ-hydroxybutyrate (P＜0.05), whereas dietary AOX significantly decreased plasmaβ-hydroxybutyrate value during the transition period (P<0.05) There were also interactions between time and treatment for plasma glutathione peroxidase activity and MDA content during the study. Cows fed high energy diets pre-partum had higher plasma glutathione peroxidase activity 3 days prior to parturition, compared with those on low energy diets. Inclusion of AOX in diets' decreased plasma glutathione peroxidase activity in cows 3 and 10 days pre-partum. Addition of AOX significantly decreased MDA values at calving (P＜0.05). Energy density induced marginal changes in fatty acid composition in the erythrocyte membrane 3 days post-partum, while AOX only significantly increased cis-9, trans-11 C18:2 conjugated linoleic acid composition. The increase in fluidity of the erythrocyte membrane was only observed in the high energy treatment. The above results indicated that feeding low energy density prepertum could improve the postpartum DMI and lactation performance. The addition of AOX is beneficial to the lactation performance by improving the lipid metabolism and antioxidative status.In summary, both the fat in the diet and lipid in the body are potentially oxidized, which could induce oxidative stress in dairy cows. The oxidative status may have a close relationship with energy metabolism. Feeding unsaturated fatty acids may result in inferior lactation performance, which is associated with inferior effect on rumen cellulolytic bacteria. Whereas, these negative effects may be partially alleviated by the addition of AOX. The effect of AOX depends on types of fatty acids. When unsaturated fatty acids were included in the diets, a significant benefit is shown by addition of AOX, but this is not the case with saturated fatty acid inclusion. A diet containing high energy density pre-partum may negatively affect the anti-oxidative status, DMI and subsequent performance. Addition of AOX may improve the anti-oxidative status and lipid metabolism, eventually resulting in improved lactation performance.