393 Beef cow antepartum glucose-insulin kinetics are altered by overfeeding metabolizable protein during late gestation and influenced by test-day relative to calving

摘要

The objective of this study was to determine whether antepartum glucose-insulin kinetics were affected when primiparous Hereford-cross heifers were fed diets containing 100 (CON; n = 10) or 133% (HMP; n = 11) of their metabolizable protein requirements from d -55.3 ± 3.7 until parturition. Intravenous glucose tolerance tests (IVGTT) were performed on d -5.4 and -7.1 ± 1.3 (CON and HMP, respectively; P = 0.34) by collecting baseline (-10 min) plasma, infusing 1.36 g glucose/kg BW0.75 via a jugular catheter, and subsequently sampling plasma for analysis of glucose and insulin. Data were analyzed with PROC GLIMMIX as a randomized block design with the fixed effects of diet, time (minute), and diet × time, considering cow (block) as a random effect. Pearson correlations were performed for IVGTT variables and test-day relative to parturition. Differences and trends were declared at P < 0.05 and 0.05 ≤ P < 0.10, respectively. Basal glucose was 13.5% greater (P = 0.048) and basal insulin tended to be 28.8% greater (P = 0.068) for HMP than CON heifers. Plasma glucose (-10 to 120 min) was greater (P = 0.047) for HMP than CON, whereas insulin was not (P = 0.54). Glucose and insulin were respectively elevated (time: P < 0.001) at 0 and 5 and 5 to 20 min and both equilibrated to baseline by 90- and 120-min. Diet × time tended to affect (P = 0.061) the glucose:insulin ratio. Test-day was correlated with time-to-max insulin (ρ = 0.60, P = 0.006), insulin clearance rate (ρ = 0.48, P = 0.027), and glucose area-under-the-curve (ρ = -0.47, P = 0.031). Time relative to calving can influence antepartum glucose-insulin kinetics. Oversupplying metabolizable protein increased baseline glucose and insulin and glucose throughout the IVGTT. Antepartum beef cattle may have altered energy partitioning that is responsive to protein consumption.