Dietary protein and(or) energy restriction in mares: plasma glucose, insulin, nonesterified fatty acid, and urea nitrogen responses to feeding, glucose, and epinephrine
1995
Sticker, L.S. | Thompson, D.L. Jr | Bunting, L.D. | Fernandez, J.M. | DePew, C.L.
Sixteen light horse mares (8 to 9 yr of age; 457 to 579 kg BW) were fed Bermudagrass hay and a corn/cottonseed hull-based supplement formulated to contain either 100% (control) or 50'7c (restricted) of the protein and(or) energy requirements for maintenance in a 2 X 2 factorial arrangement of treatments. Daily measurements of intake, BW, and plasma hormones and metabolites were made for 33 d. Plasma glucose, insulin, NEFA, and urea N were measured in hourly samples drawn on d 27, and parallel with an i.v. glucose tolerance test (IVGTT) and epinephrine challenge on d 29. Energy restriction increased daily NEFA concentrations (P < .001) and urea N (P = .013), whereas protein restriction decreased (P = .002) urea N concentrations. These effects of protein and energy restriction occurred within 24 h and were consistent (day effect, P > .1) throughout the remaining 24 d. Normal meal consumption elevated plasma glucose, insulin, and urea N concentrations (time effect, P < .08). Plasma NEFA concentrations did not change after feeding in mares fed control energy, but decreased in mares fed restricted energy (energy X time interaction, P = .005). After IVGTT, areas under the curve for plasma glucose and insulin were smaller in mares fed restricted protein (P < .05), whereas glucose area was larger in mares fed restricted energy (P = .009). After epinephrine injection, energy restriction increased the initial magnitude of the NEFA response, but after 50 min, reduced plasma NEFA below pre-injection concentrations (energy X time interaction, P = .06). We conclude that metabolic responses occur within 24 h of dietary changes and that plasma constituents are altered by protein and(or) energy restriction during feeding, glucose, and epinephrine challenges.
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