Glucose, insulin, and feed restriction challenges reveal altered glucose and insulin dynamics in Temperamental steers
Temperamental cattle are behaviorally, physiologically, and immunologically different than Calm cattle. Recently the dramatic metabolic differences between Temperamental and Calm cattle have been elucidated; Temperamental cattle appear to maintain greater concentrations of NEFAs when compared to Calm cattle, which may influence other metabolic parameters including glucose and insulin. The objective of this study was to determine whether temperament influences cattle’s metabolic responses to a glucose tolerance test (GTT), insulin sensitivity test (IST) and feed restriction (FR). Angus-cross steers (16 Calm and 15 Temperamental; 216±6 kg BW) were selected based on weaning Temperament Score. On d1 steers were moved into indoor individual stanchions to allow measurement of feed intake. Feed and water was provided ad libitum from d1-7. On d6 steers were fitted with indwelling rectal temperature probes and jugular catheters, and were returned to individual stanchions. At 0900h on d7 steers received the GTT (0.5 mL/kg BW of a 50% dextrose solution) and at 1400h steers received the IST (2.5 IU bovine insulin/kg BW). Feed was removed for 72h beginning at 0800 h on d8, and was provided at 25%, 50%, 75%, and 100% of ad libitum on d11, 12, 13, and 14, respectively. Blood samples were collected at 15- and 30-min intervals from -60 to 150 min relative to the GTT and IST, and every 6h from 0 to 156h during the FR challenge. Serum was isolated and stored at -80oC until analyzed for glucose, insulin, NEFA, and blood urea nitrogen (BUN). All variables changed over time (P<0.01). For the duration of the study, Temperamental steers maintained greater (P<0.01) NEFA and decreased (P≤0.01) BUN and insulin sensitivity (measured using RQUICKI) compared to Calm steers. During the GTT Temperamental steers had greater (P<0.01) glucose, decreased (P=0.03) insulin, and had greater glucose disappearance (P=0.03) yet decreased insulin:glucose (P<0.01). During the IST, Temperamental steers had decreased (P=0.04) glucose and greater (P<0.01) insulin and a greater insulin:glucose (P<0.01). For the duration of the FR challenge, Temperamental steers maintained greater (P=0.001) glucose and decreased (P=0.001) insulin than Calm steers. These data demonstrate that differences exist in the manner that Temperamental steers respond to glucose, insulin, and FR. These differences exist due to a complex, yet undefined paradigm involving stress, immune, and metabolic parameters, ultimately resulting in greater NEFA, insulin insensitivity, and reduced glucose disappearance. These differences accentuate the need for different management strategies for feeding Temperamental versus Calm cattle.
Keywords: cattle, metabolism, temperament