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) (Ametaj, Emmanuel, Zebeli, & Dunn, 2009; Dong et al., 2011; Nocek, 1997), a well recognized digestive disorder, which leads to enhanced release of lipopolysaccharide (LPS) in the rumen as well as the lower gut (Dong et al., 2011). The LPS is a cell‐wall component of Gram‐negative bacteria, commonly known as endotoxin. Studies have demonstrated that feeding high‐concentrate diets can trigger an inflammatory response in dairy cows, resulting in increased release of proinflammatory cytokines such as interleukin‐1 (IL‐1), IL‐6, and tumour necrosis factor‐α (TNF‐α) and a rise of the acute phase proteins (APP) such as serum amyloid A (SAA), LPS‐binding protein (LBP), C‐reactive protein (CRP) and haptoglobin (Hp) in blood of dairy cows (Dong et al., 2011). However, there is a lack of evidence to link the inflammatory response directly with LPS because the blood LPS was not always detected under the condition of a high‐concentrate diet (Plaizier, Khafipour, Li, Gozho, & Krause, 2012), although studies have shown that a single intravenous administration of large doses of LPS (≥1 μg LPS/kg body weight, BW) was associated with enhanced plasma concentrations of cytokines, such as TNF‐α, IL‐1, interferon‐γ (IFN‐γ), and APP, such as SAA, LBP, CRP and Hp in dairy cows (Carroll et al., 2009; Werling et al., 1996). It has also been demonstrated that a short‐term (100 min) intravenous infusion of LPS at doses greater than 0.5 μg LPS/kg BW reduced dry matter intake and milk yield in dairy cows (Waldron, Nishida, Nonnecke, & Overton, 2003). Nonetheless, in practical production, dairy cows may oftentimes encounter long‐term and low‐dose LPS exposure when they are fed high‐concentrate diets or subjected to poor hygienic environments. Furthermore, to the best of our knowledge, there are no reports dealing with the effects of LPS infusion on milk fat and protein profiles in dairy cows. Therefore, we hypothesized that if LPS gains entry to the body continuously even at a low‐dose, it might induce an inflammatory response, reduce milk production, and alter milk fatty acid (FA) and amino acid (AA) profiles in dairy cows. The objective of this study was to evaluate the effects of low‐dose infusion of LPS (0.01 μg LPS/kg BW) from Escherichia coli O111:B4 for a time frame of 7 days on inflammatory responses, milk production and milk quality in mid‐lactating Holstein cows.