Abstract
PurposeThe mechanism underlying the decline in milk quality during periods of feeding high-concentrate diets to dairy ruminants is not well documented. The aim of this study was to investigate the metabolic changes in the liver that contribute to the input of substrate precursors to the mammary gland after feeding a high-concentrate diet to lactating goats for a long period.Experimental DesignEight mid-lactating goats with rumen cannulas were randomly assigned to two groups. For 9 weeks, the treatment group was fed a high-concentrate diet (60% concentrate of dry matter, HC) and the control group was fed a low-concentrate diet (40% concentrate of dry matter, LC). Ruminal fluid, plasma, and liver tissues were sampled, microarray techniques and real-time polymerase chain reaction were used to evaluate metabolic parameters and gene expression in liver.ResultsFeeding a 60%-concentrate diet for 9 weeks resulted in a significant decrease in rumen pH. Changes in fat and protein content also occurred, which negatively affected milk quality. Plasma levels of leptin (p = 0.058), non-esterified fatty acid (p = 0.071), and glucose (p = 0.014) increased markedly in HC group. Plasma cortisol concentration was significantly elevated in the treatment group (p<0.05). Expression of the glucocorticoid receptor protein gene was significantly down-regulated (p<0.05) in the liver. The expression of genes for interleukin 1β, serum amyloid A, C-reactive protein, and haptoglobin mRNA was significantly increased (p<0.05) in the HC group. GeneRelNet analysis showed that gene expression involved in inflammatory responses and the metabolism of lipids, protein, and carbohydrate were significantly altered by feeding a high-concentrate diet for 9 weeks.ConclusionsActivation of the acute phase response and the inflammatory response may contribute to nutrient partitioning and re-distribution of energy in the liver, and ultimately lead to a decline in milk quality.
Highlights
Dairy ruminants are often fed a high-concentrate diet to meet the energy requirements of high milk production
GeneRelNet analysis showed that gene expression involved in inflammatory responses and the metabolism of lipids, protein, and carbohydrate were significantly altered by feeding a high-concentrate diet for 9 weeks
Activation of the acute phase response and the inflammatory response may contribute to nutrient partitioning and re-distribution of energy in the liver, and lead to a decline in milk quality
Summary
Dairy ruminants are often fed a high-concentrate diet to meet the energy requirements of high milk production. Metabolic disorders such as subacute ruminal acidosis (SARA) can result from feeding excessive amounts of high proportions of fermentable concentrate and forage with low physically effective fiber [1]. SARA is a common digestive disorder in most dairy herds. Production costs from SARA have been estimated to be as high as $1.12 per cow per day [7]. In the regions shortage of high quality forage and lack of reasonable feeding management practices prevents dairy cows from achieving their genetic potential for milk production
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