Dairy cows are often fed high concentrate diet (HC) to meet the nutritional demands of lactation.However, overfeeding cattle with a diet rich in concentrate for long-term results in a metabolic disorder termed subacute ruminal acidosis (SARA).One consequence of SARA is the depression of milk quality and quantity and previous studies indicated SARA reduced milk protein production.The rumen contains gram-negative bacteria, of which lipopolysaccharide (LPS) is an important cell wall component.Feeding cattle with HC decreases the rumen pH level causing gram-negative bacteria to be lysed in the rumen and releasing free endogenous LPS.LPS can then translocate into the bloodstream from the digestive tract and enter the mammary gland, initiating inflammatory responses that result in reduced productivity of the animal.The present study was conducted to investigate the effects of endogenous LPS released in the rumen on inflammatory responses and casein synthesis in mammary glands of lactating dairy cows fed HC.Eight lactating Holstein cows [(455 ± 28)kg live weight] fitted with a rumen fistula were randomly divided into two groups.