Effects Of Continuous Low Dose Infusion Of Lipopolysaccharide On Inflammatory Responses, Milk Production And Milk Quality In Dairy Cows

In dairy industry, it is a common practice to feed dairy cattle diets with a high proportion of concentrate in order to raise milk yield. However, these diets are associated with the high incidence of subacute ruminal acidosis(SARA), which leads to enhanced release of lipopolysaccharide(LPS) in the rumen as well as the lower gut. And then it will cause a series of interrelated reactions, such as resulting pro-inflammatory, mastitis, laminitis etc. accordingly affecting the performance of the animal. This study mainly simulated the real conditions of high proportion of concentrate or poor hygienic environments in the large-scale production of dairy cows, to evaluate the effects on inflammatory responses, milk production and milk quality in mid-lactating Holstein cows.Eight clinically healthy, second-parity Holstein cows, with a body weight(BW) of 554±19 kg in mid-lactation, were randomly allocated to 1 of the 2 treatments, according to a randomized block design. The 4 cows assigned to intravenous saline(9 g/L Na Cl) infusion constituted the control group. The other 4 cows received LPS infusion(Escherichia coli O111:B4) with the dose of 0.01μg LPS/kg BW. The experiment lasted 7 days for approximately 6 hours each day. The clinical symptoms and milk production performance were observed. Milk samples were analyzed for conventional components, fat acids and amino acids. And jugular vein and mammary vein plasma samples were analyzed for concentrations of cytokines, acute phase proteins(APPs) and LPS. The results were as follows:(1) The body temperature of the cows extremely significantly increased(p=0.0039) after being infused with 0.01 μg/kg BW LPS. And the respiratory rate showed a rising trend(P<0.10).(2) Compared with control, the dry matter intake(DMI) of the treatment group was highly significantly decreased(P<0.01), and the milk yield and milk protein content were significantly reduced(P<0.05). Furthermore, the LPS concentration of milk was significantly higher(P<0.05) than that of control. According to the correlation analysis, the performance of milk production(milk yield, 4% FCM milk, milk fat yield and milk protein yield) was negative correlated with LPS-infusion. Among them, 4% FCM milk was significantly negative correlated with the LPS-infusion(r=-0.4274, P<0.05), and milk yield was highly significantly negative correlated with the LPS-infusion(r=-0.7331,P<0.01).(3) LPS-infused affected the concentrations of interleukin 1β(IL-1β)(P<0.05), and the concentrations of C-reactive protein(CRP), Haptoglobin(Hp), LPS-binding protein(LBP), and serum amyloid protein(SAA) were markedly increased(P<0.01) after LPS infusion, which showed that the continuous and low dose of LPS induced the acute phase response and the changes of cytokines.(4) The content of C17:1 among the odd- and branched-chain fat acids was extremely significantly reduced after being LPS-infused(P<0.01). The contents of C18:0, C18:1n9(trans) and C18:2n6(trans) from C18 saturated and unsaturated fat acids were also decreased after the infusion(P<0.05). In addition, the contents of amino acids in milk also had a great change. The contents of Met, Tyr, Thr, Ser and Pro were decreased, the contents of Phe, Val, Glu, Gly, Lys and total amino acids were significantly decreased(P<0.05), and the contents of ILe, Arg, Leu, Asp and Ala were highly significantly decreased(P<0.01).Results suggest that the lactating dairy cows infused with LPS at a physiological concentration, increased the body temperature, decreased feed intake and reduced the milk yield. And the milk quality as well as the chemical composition of milk fat and milk protein were also changed. After being infused with LPS, the LPS contents of the jugular vein and mammary vein were increased, and the content of LPS in the milk was also increased. Moreover, the concentrations of IL-1β and APPs(CRP, Hp, LBP and SAA) were increased in the blood.