Short communication: Glucose infusion into early postpartum cows defines an upper physiological set point for blood glucose and causes rapid and reversible changes in blood hormones and metabolites

Abstract

Low blood glucose concentrations after calving are associated with infertility in postpartum dairy cows perhaps because glucose is a master regulator of hormones and metabolites that control reproductive processes. The hypothesis was that low blood glucose postpartum is caused by inadequate glucose entry rate relative to whole-body demand as opposed to the alternative possibility that postpartum cows have a lower regulatory set point for blood glucose. Eight early postpartum (10 to 25 d) dairy cows (5 Holstein and 3 Guernsey) were jugular catheterized. During the first 24 h, cows were infused with physiological saline at 83.3 mL/h. After 24 h, the infusion solution was switched to 50% dextrose that was infused at a rate of 41.7 mL/h (total daily glucose dose=500 g). On d 3 and d 4, the rate of glucose infusion was increased to 83.3 mL/h (daily dose=1,000 g) and 125 mL/h (daily dose=1,500 g), respectively. On d 5, physiological saline was infused at 83.3 mL/h. Blood was sampled hourly through a second jugular catheter (contralateral side) and analyzed for glucose, nonesterified fatty acids, β-hydroxybutyrate, insulin-like growth factor 1, and insulin. Blood glucose concentrations on d 1 (saline infusion) averaged 53.4±1.7 mg/dL. Blood glucose concentrations increased on d 2 when cows were infused with 500 g/d and increased further on d 3 when cows were infused with 1,000g of glucose/d. Increasing the infusion rate to 1,500 g/d on d 4 did not cause a further increase in blood glucose concentrations. Based on a segmented regression analysis, the upper physiological set point for blood glucose was 72.1 mg/dL. Both insulin and insulin-like growth factor 1 concentrations increased in response to glucose infusion and decreased when cows were infused with saline on d 5. Serum nonesterified fatty acids and β-hydroxybutyrate concentrations decreased in response to glucose infusion and rebounded upward on d 5 (saline infusion). In conclusion, early postpartum cows had circulating blood glucose concentrations that were well below the upper set point defined in this study (72.1 mg/dL). Infusing approximately 1,000 g of glucose daily increased blood glucose to the physiological set point and rapidly changed the hormonal and metabolic profile that typifies postpartum cows. The inability of the early postpartum cow to achieve an adequate entry rate for glucose relative to whole-body demand is a possible mechanism that links postpartum physiology and nutrition to reproduction in dairy cows.

Hyperglycaemia in transition dairy cows: Effects of lactational stage and conjugated linoleic acid supplementation on glucose metabolism and turnover

“…Confirming earlier findings of Kahn and Flier (2000), De Koster et al (2015) concluded that the inhibiting effect of insulin on lipolysis occurs at much lower concentrations than the stimulatory effect of insulin on glucose clearance. Lucy et al (2013) further suggest an insulin-independent effect of exogenous glucose on the glucosefatty acid cycle as observed earlier by Hue and Taegtmeyer (2009).…”

“…Lucy et al. () further suggest an insulin‐independent effect of exogenous glucose on the glucose–fatty acid cycle as observed earlier by Hue and Taegtmeyer (). At the low basal concentrations of insulin after parturition, however, lipolysis is not inhibited resulting in elevated free fatty acid concentrations in plasma supporting the metabolic priority of the mammary gland.…”

“…No differences between CLA and CON were detected. Although not during hyperglycaemic clamps and not always in transition cows, numerous studies showed the decline in plasma fatty acids and BHB after glucose application (as bolus or continuous intravenous infusion and abomasal infusion; e.g., Treacher, Baird, & Young, ; Jaakson et al., ; Lucy, Escalante, Keisler, Lamberson, & Mathew, ; De Koster et al., ). In non‐lactating cows, Vieira et al.…”

Changes in serum metabolic hormone levels after glucose infusion during lactation cycles in Holstein cows

“…Other researchers also mentioned acute decreases in circulating IGF-1 in response to increases in insulin or glucose. 15 It may be suggested that glucose had the obvious effect on metabolism of this hormone in dairy cows. Damptey et al showed that IGF-1 concentration was positively correlated with insulin (r=0.377; P<0.001) and glucose (r=0.249; P<0.05).…”

“…14 Insulin like growth factor-1 (IGF-1) also considered as a metabolic hormone that bind to insulin receptors and has a key role in metabolism of glucose in high producing dairy cows. 15 Since the cows have several metabolic sates whit disproportions between energy input and output, the aim of the present study was to reveal the effect of glucose, as an energy source, on metabolic hormones levels at each state. Hence, the changing pattern of thyroid hormones, cortisol and IGF-1 was followed after bolus intravenous glucose administration in high producing Holstein dairy cows at different metabolic states and these changes were compared together.…”