Tranfer Of Dietary Aflatoxin B1into Milk And Its Effects On Productive Performance And Health In Dairy Cows

In the current dairy farming, dairy cows ingest aflatoxin B1(AFB1)-contaminated feed, which often causes aflatoxin M1(AFMl) contamination in milk and milk products. This study was conducted to investigate:(1) transfer rate of dietary AFB1into milk;(2) Clearance pattern in milk AFM1after removal of AFB1from diet;(3) the effect of AFB1fed on productive performance and healthy condition in dairy cows; and (4) the effect of dietary inclusion of SM on the above-mentioned variables. The experiments and main results obtained are summarized as below.1. Seasonal variation of aflatoxin Bl in feed and aflatoxin Ml in raw milk in Yangtze River Delta region of China (Exp.1)The objective of the study was to evaluate the occurrence of AFB1in total mixed ration (TMR) and AFM1in raw milk from18dairy farms in Yangtze River Delta region in four seasons. A total of60TMR samples were collected with15samples each season, and72milk tank samples were collected with18samples each season. Feed AFB1was tested using HPLC-FLD and milk AFM1was detected using LC-MS/MS method. The differences in the concentration of feed AFB1and milk AFMl among four seasons were analyzed with a one-way ANOVA procedure. With detection limit of0.300μg/kg, AFB1was found to be positive in28TMR samples (46.7%) ranging from0.332to4.040μg/kg. A higher AFB1concentration in TMR was observed in winter than that in spring and autumn (P<0.05), with no difference with summer. Milk AFM1was found to be positive in43milk samples (59.7%) ranging from0.01to0.42μg/L with detection limit of0.01μg/L. The concentration of AFM1in raw milk was significantly higher during the winter (0.123μg/L) than that in other seasons (P<0.05). There was no significant difference among the spring (0.029μg/L), summer (0.032μg/L), and autumn (0.032μg/L)(P>0.05) seasons. These result indicated that there is large variation in the occurrence of feed AFB1and milk AFMl during different seasons. The feed in winter and summer is in high risk for AFB1, while the milk in winter is in high risk for AFM1, suggesting that seasonal factors should be considered for control of aflatoxin in both the feed and milk. 2. Transfer of dietary AFB1to milk AFM1and effect of dietary inclusion of SM in dairy cows (Exp.2)The objectives of this study was to investigate the transfer rate of AFB1from feed to milk and clearance pattern of milk AFM1after termination of dietary AFB1administration, and to evaluate the effects of SM on milk AFM1, plasma biochemical variables and ruminal fermentation of dairy cows fed varying doses of AFB1. Three equal groups of8multiparous Holstein cows in late lactation (DIM=271±29d; Milk yield=21.6±3.1kg/d) were assigned to one of three trials in a crossover design. Cows in Trial1received no aflatoxin, cows in Trial2received20μg of AFB1/kg of diet DM, and cows in Trial3received40μg of AFB1/kg of diet DM. Cows in each trial were assigned to1of2treatments:control or0.25%SM. Each trial consisted of2consecutive periods with pre-trial for4d (d1to4), AFB1challenging for7d (d5toll) and clearing for5d (d12to16). In each period, samples of TMR and milk were collected on d1,2and10to14of each period. Blood samples (10mL) were collected from the coccygeal vein into heparinized vacuum tubes before the morning feeding on d1,11and14. Rumen fluid (50mL) was collected by oral stomach tube2h after the morning feeding on d1and11. Background level of milk AFM1was0.003μg/L. When cows were fed with20or40μg/kg AFB1-contaminated diets, average contents of milk AFM1were0.105and0.209μg/L, respectively, and transfer rates of dietary AFB1into milk were0.56and0.59%, respectively. Milk AFM1could be thoroughly cleared3days after dairy cows were fed AFB1-free diet. Adding SM in the20μg/kg of AFB1-contaminated diet decreased the milk AFM1concentration (0.105vs.0.088μg/L) and the transfer of aflatoxin to milk (0.56vs.0.46%), but they were not affected by addition of SM in the40μg/kg of AFB1-contaminated diet. Addition of SM to the basal diet increased overall ruminal concentrations of volatile fatty acid (VFA,99.6vs.94.2mM, P<0.05), microbial cell protein (MCP,3.3vs.2.9mg/mL, P<0.05) and carboxymethy cellulase (CMCase) activity (0.34vs.0.26U, P<0.05). Adding SM in the20μg/kg of AFB1-contaminated diet increased the total VFA concentration (99.8vs.93.4mM, P<0.05), MCP level (3.2vs.2.7mg/mL, P<0.05) and CMCase activity (0.28vs.0.22U, P=0.07), but they were not affected by addition of SM in the40μg/kg of AFB1-contaminated diet. Adding SM to basal or AFB1-contaminated diets at0.25%(DM basis) had no effect on lactation performance, liver function and humoral immunity, but significantly decreased indicators of body oxidative stress. From the results obtained in this experiment, it is concluded that transfer rate of dietary AFB1 into milk AFM1ranged from0.46to0.59%and milk AFM1can be cleaned within3d; adding SM did not affect milk yield and compositon of dairy cows in late lactation, but decreased milk AFM1concentration and improved healthy condition in dairy cows fed the diet contaminated with20μg/kg AFB1.3. Effects of long-term challenge of AFB1on productive performance and healthy condition in dairy cows (Exp.3)The objective of the study was to evaluate produtive performance and healthy condition in dairy cows exposed to long-term challenge of AFB1, and to study the effect of SM inclusion. Forty dairy cows were blocked into4groups based on days in milk (33±7; mean±SD) and milk production (33.9±3.1kg; mean±SD), and were randomLy assigned to1of4treatments in a2×2factorial arrangements with AFB1(0or20μg/kgDM) and SM (0or0.25%of DM) as main factors. The experiment lasted for9weeks, with the first week for adaptation. Milk yield and milk composition were recorded weekly, and plasma biochemical variables and ruminal fermentation were analyzed in the first and the last week of the experiment. Milk AFM1was analyzed by HPLC-MS/MS. Variables of data were analyzed using the mixed procedure of SAS. Dry matter intake, milk yield, contents of milk protein and milk fat, and linear somatic cell count averaged23.9kg/d,35.5kg/d,2.9%,3.6%, and5.1, respectively, and were not affected (P>0.05) by either AFB1or SM addtion. Addition of SM in AFB1-contaminated diet significantly reduced (P<0.01) milk AFM1concentration (0.191vs.0.134μg/L) and transfer rates of dietary AFB1into milk AFM1(1.38vs.0.89%). Compared to the cows fed non-AFB1diet, Dairy cows fed AFB1-contaminated diet had lower level of superoxide dismutase activity, total antioxidative capacity, glutathione peroxidase, IgG and IgA (P<0.05), and higher level of malondialdehyde in plasma (P<0.05). Inclusion of SM into diets increased the plasma superoxide dismutase activity, total antioxidant capacity, and IgG, but decreased malondialdehyde (P<0.05). Neither AFB1nor SM affected the plasma levels of alanine transaminase, aspartate aminotransferase, total bilirubin, and alkaline phosphatase and IgM (P>0.05). The AFB1did not affect ruminal fermentation parameters, except for decreasing CMCase activity. However, addition of SM increased the level of ammonia-N, MCP, VFA and CMCase and decreased the pH value, but the individual VFA proportion, and other ruminal enzyme activity were not influenced by SM. It is indicated from this experiment that transfer rate of dietary AFB1into milk was higher than that for late-lactation cows; adding SM did not affect milk yield and compositon of dairy cows in early to mid lactation, but decreased milk AFM1level and improved adverse healty condition in dary cows exposed to long-term challenge of AFB1.In Summary, seasonal difference in TMR AFB1and milk AFM1should be considered for the safe milk production in the dairy farms of Yangtze River Delta region. The transfer rate of dietary AFB1into milk AFM1ranged from0.89to1.38%or0.46to0.59%in early-to-mid-or late lactating dairy cows, respectively. The AFM1can be cleaned within3d from the milk of dairy cow receiving an AFB1-contaminated diet. Adding SM or AFB1did not affect milk yield and compostion, while SM addtion decreased the transfer rate and improved healty condition in dairy cows.