Abstract
To meet the nutrition requirements of lactation, dairy cows are usually fed a high concentrate diet (HC). However, high-grain feeding causes subacute ruminal acidosis (SARA), a metabolic disorder that causes milk protein depression. This study aimed to investigate the effect of lipopolysaccharide (LPS) released in the rumen on inflammatory gene expression and casein synthesis in mammary glands of lactating dairy cows fed a HC diet. We found that milk protein was significantly decreased in the HC group after 15 weeks of feeding. Overall, LPS concentrations in the rumen fluid, lacteal artery and vein were increased in the HC group. Transcriptome microarray was used to evaluate alterations in the signaling pathway in mammary glands. Signaling pathways involved in inflammatory responses were activated, whereas those involved in protein synthesis were inhibited in the HC group. mRNA expression involved in inflammatory responses, including that of TLR4, NF-кB and pro-inflammatory genes, was increased in the HC group, while αs1-casein (CSN1S1), β-casein (CSN2), mTOR and S6K gene expression were decreased. Moreover, protein expression was consistent with the corresponding gene expression. After feeding with an HC diet, LPS derived from the rumen increased inflammatory gene expression and inhibited casein synthesis in the mammary glands of lactating dairy cows fed a HC diet.
Highlights
Dairy cows are often fed a high concentrate diet (HC) to meet the nutritional demands of lactation
Signaling pathways involved in inflammatory responses were activated, whereas those involved in protein synthesis were inhibited in the HC group. mRNA expression involved in inflammatory responses, including that of TLR4, NF-кB and pro-inflammatory genes, was increased in the HC group, while αs1-casein (CSN1S1), β-casein (CSN2), mTOR and S6K gene expression were decreased
In www.impactjournals.com/oncotarget addition, the results showed that 45 signaling pathways were inhibited >2-fold in the HC group compared with the low concentrate diet (LC) group (Figure 3B), of which protein processing in the endoplasmic reticulum and the phosphatidylinositol 3-kinase (PI3K)-AKT1-mTOR signaling pathway were involved in protein synthesis
Summary
Dairy cows are often fed a high concentrate diet (HC) to meet the nutritional demands of lactation. The long-term overfeeding of cattle with a diet rich in concentrate results in a metabolic disorder termed subacute ruminal acidosis (SARA), in which the rumen pH falls below 5.6 for more than 3 hours per day [1]. 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 [6]. LPS can be translocated into the bloodstream from the digestive tract [7] and enter the mammary gland, initiating inflammatory responses that result in reduced productivity of the animal [8, 9]
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