Endocrine and metabolic responses of high producing Holstein dairy cows to glucose tolerance test based on the stage of lactation

Helping the high producing dairy cows to diminish negative energy balance can improve their metabolism. Glucose administration by supplying energy source may alter metabolic responses of dairy cows to prevent metabolic disorders. Hence, the aim of the present study was to evaluate the metabolic responses of dairy cows to bolus intravenous glucose administration via assessing the circulating metabolic biomarkers. Twenty five multiparous Holstein dairy cows were divided into 5 equal groups containing early, mid and late lactations, far-off and close-up dry periods. All cows received dextrose 50% intravenously at 500 mg/kg, 10 ml/kg/hour. Blood samples were collected from all animals prior to and I, 2, 3 and 4 h after dextrose 50% infusion and sera were separated to determine glucose, insulin, beta-hydroxy butyric acid (BHBA), non-esterified fatty acid (NEFA), lipid profile, thyroid hormones, cortisol and insulin like growth factor-1. The rapid and significant increase in patterns of glucose and insulin concentrations was seen in early and mid lactation and close-up dry cows after glucose administration. Despite the increased levels of insulin in early and mid lactation and close-up dry cows, glucose concentrations were not decreased near the base line levels at 4th hour. The significant decrease in patterns of NEFA and BHBA was seen in early and mid lactation and close-up dry cows after glucose administration. The significant decrease and increase in patterns of triiodothyronine (T3) and thyroxine (T4) concentrations were detected in all studied animals, respectively. IGF-1 was significantly decreased following glucose infusion in mid- and late lactations and far-off dry groups. As a conclusion, bolus intravenous glucose infusion could influence the metabolism of high producing Holstein dairy cows. The metabolic responses to glucose indicated that glucose is an important direct controller of metabolic interactions in high producing Holstein dairy cows during different metabolic states. (C) 2015 Elsevier B.V. All rights reserved.