Acute Metabolic Responses of Postpartal Dairy Cows to Subcutaneous Glucagon Injections, Oral Glycerol, or Both¹

Plasma glucagon concentrations of cows treated with saline, glycerol, glucagon, or glucagon plus glycerol (GlucGlyc) on d 1, 7, and 13 postpartum. Subcutaneous glucagon injections, given either alone or in combination with glycerol, increased plasma concentrations of glucagon during the first 4 and entire 8h after injections on d 1, 7, and 13 postpartum, respectively (all P<0.001, SEM = 0.13 to 0.23). Precisely, glucagon effect on plasma glucagon concentration was significant between 15 and 300min (P=0.04 and P=0.05), between 15min and 210min (P=0.0001 and P=0.02), and between 15 and 210min (P=0.003 and P=0.02) on d 1, 7, and 13 postpartum, respectively. Glucagon plus glycerol effect was significant between 15 and 360min (P=0.003 and P=0.04), between 15 and 210min (P=0.0003 and P=0.02), and between 15 and 180min (P=0.008 and P=0.02) on d 1, 7, and 13 postpartum respectively. Glucagon plus glycerol also tended to increase plasma glucagon at 240 and 300min (P=0.05 and P=0.06) on d 7 postpartum. Oral glycerol decreased plasma glucagon concentrations during the first 4h postadministration on d 1, 7, and 13 (P=0.05, P=0.04, and P=0.05, respectively; SEM = 0.10 to 0.21) with the effect being nonsignificant for the entire 8-h period (P=0.15, P=0.12, and P=0.14, respectively). No significant effects of day (P=0.12) and treatment×day (P=0.90) on plasma glucagon concentrations were observed.

Plasma glucose (panels A, B, and C) and insulin (panels D, E, and F) concentrations on d 1, 7, and 13 postpartum in cows treated with saline (n=4), glucagon (n=4), glycerol (n=6), or glucagon plus glycerol (GlucGlyc; n=6). For plasma glucose, effects of glucagon were not significant (P≥0.34) during the first 4h or the entire 8-h period on d 1, although a significant effect was detected between 60 and 120min (P=0.02 and P=0.05, respectively). Glucagon effect became significant (P ≤0.03; SEM=0.06 to 0.10) on d 7 and 13 postpartum. In particular, glucagon effect was significant between 15 and 240min (P=0.0001 and P=0.02) and between 30 and 240min (P=0.03 and P=0.02) on d 7 and 13 postpartum, respectively. Overall, effect of treatment and the interaction of treatment×day were significant (P≤0.03) and effect of day was not (P=0.15). Effect of glycerol was not significant (P≥0.22; SEM=0.06 to 0.09) on d 1 and 13 postpartum, although it was significant at 100 and 120min (P=0.04 and P=0.04, respectively) with a tendency at 80min (P=0.07). However, it became significant (P=0.04) during the first 4h and tended (P=0.06) to be significant over the 8-h periods on d 7 postpartum. Overall, effects of treatment, day, and the interaction of treatment×day were not significant (P≥0.11). Glucagon plus glycerol effects were significant (P≤0.008; SEM=0.06 to 0.10) during the first 4h and entire 8h on d 1, 7, and 13 postpartum. Glucagon plus glycerol effects were significant between 15 and 210min (P=0.003 and P=0.01), between 15 and 300min (P=0.002 and P=0.003), and between 30 and 240min (P=0.004 and P=0.03) on d 1, 7, and 13, respectively. Effect of glucagon plus glycerol tended (P=0.07) to be synergistic on d 1. Overall, the effect of treatment was significant (P=0.0001) and those of day and interaction of treatment×day were not significant (P≥0.31). For insulin, effect of glucagon during the first 4h was not significant (P=0.32) on d 1, but was significant (P≤0.004) on d 7 and 13 postpartum. During the entire 8-h period, glucagon effects were significant (P≤0.04) on d 1 and 7 and not (P=0.22; SEM 0.16 to 0.27) on d 13 postpartum. Glucagon effect was significant between 15 and 210min (P=0.01 and P=0.04) on d 7 and between 60 and 210min (P=0.03 and P=0.04, respectively) on d 13 postpartum. Overall, effects of treatment, day, and the interaction of treatment×day were significant (P≤0.01). Glycerol did not influence (P≥0.33; SEM = 0.15 to 0.25) plasma insulin on any day. Overall, effects of treatment and the interaction of treatment×day were not significant (P≥0.25). Effect of day was significant (P=0.01). Effects of glucagon plus glycerol were significant (P≤0.01; SEM = 0.15 to 0.24) at all times on d 1, 7, and 13 postpartum. In particular, the effect of glucagon plus glycerol was significant between 60 and 300min (P=0.0009 and P=0.01), between 15 and 240min (P=0.002 and P=0.01), and between 60 and 240min (P=0.01 and P=0.02). Overall, effects of the treatment were significant (P<0.0001) and synergistic (P=0.02). Effect of day was significant (P=0.01), but the interaction of treatment×day was not significant (P=0.47).

Plasma NEFA (panels A, B, and C) and BHBA (panels D, E, and F) concentrations on d 1, d 7, and d 13 postpartum in cows treated with saline (n=4), glucagon (n=4), glycerol (n=6), or glucagon plus glycerol (GlucGlyc; n=6). For NEFA, glucagon effects did not differ (P=0.76) at any time on d 1 and differed (P≤0.04; SEM = 0.16 to 0.25) during the first 4h, but were not different (P≥0.13) during the 8-h period on d 7 and 13. Precisely, glucagon effect was significant between 120 and 240min (P=0.02 and P=0.03, respectively) on d 7 and between 100 and 240min (P=0.04 and P=0.04, respectively) overall, whereas effects of treatment and the interaction of treatment×day were significant (P≥0.003), effect of the day was not (P=0.13). Glycerol effects were highly significant (P≤0.01; SEM = 0.15 to 0.24) at all times on d 1, 7, and 13. Glycerol effect was significant between 60 and 360min (P=0.02 and P=0.002) on d 1, between 80 and 240min (P=0.03 and P=0.04) on d 7, and between 45 and 300min (P=0.004 and P=0.05, respectively) on d 13 postpartum. Overall, treatment and the interaction the treatment×day effects were significant (P ≤0.05) and day effect was not (P=0.13). Effects of glucagon plus glycerol were significant (P≤0.005; SEM = 0.15 to 0.23) during the first 4h on d 1, 7, and 13 postpartum. Over the entire 8-h period, these effects were significant (P≤0.03) only on d 7 and 13, but not (P=0.25) on d 1 postpartum. Precisely, glucagon plus glycerol treatment effect was significant between 80 and 300min (P=0.04 and P=0.03) on d 1, between 30 and 210min (P=0.02 and P=0.04) on d 7, and between 45 and 300min (P=0.004 and P=0.05, respectively) on d 13 postpartum. Overall, effect of treatment was significant (P=0.0001), but effects of day and the interaction of treatment×day were not significant (P≥0.30). For plasma BHBA, glucagon effect was not significant (P≥0.21; SEM = 0.11 to 0.16) during the first 4h or entire 8h on d 1, 7, and 13. However, glucagon tended to increase BHBA at 360 and 420min (P=0.09 and P=0.09, respectively) and increased BHBA at 480min (P=0.03). Overall, effects of treatment and the interaction of treatment×day tended to be significant (P≤0.06). Effect of day was not significant (P=0.25). For BHBA, glycerol effects were significant (all P=0.01; SEM = 0.10 to 0.16) during the first 4h and entire 8h on d 1 postpartum. Effect of glycerol was significant between 120 and 300min (P=0.04 and P=0.02, respectively). On d 7 postpartum, glycerol did not affect (P=0.13) BHBA concentration during the first 4h. Over the entire 8-h period, glycerol effect became significant (P=0.04). This effect was most significant at 240min (P=0.03). No effect (P≥0.21) of glycerol was detected on d 13 postpartum. Overall, effect of treatment was significant (P=0.003) and effects of day and the interaction of treatment×day were not (P≥0.25). Effects of glucagon plus glycerol were significant (P≤0.04) during the first 4h on d 1 and 7 postpartum and continued to be significant (P≤0.04; SEM=0.10 to 0.15) over the entire 8-h period on the same days. Precisely, the glucagon effect was significant between 120 and 240min (P=0.05 and P=0.008) with a tendency at 300 and 420min (P=0.06 and P=0.05, respectively). No effect (P ≥0.35) was detected on d 13 postpartum. Overall, effect of treatment was significant (P=0.002) and synergistic (P=0.05), but effects of day and the interaction of treatment×day were not significant (P≥0.25).

Blood urea nitrogen (panels A, B, and C) and plasma triacylglycerol (TAG, panels D, E, and F) concentrations on d 1, 7, and 13 postpartum in cows treated with saline (n=4), glucagon (n=4), glycerol (n=6), or glucagon plus glycerol (GlucGlyc; n=6). For BUN, glucagon effect was not significant during the first 4 or entire 8h on d 1, 7, and 13 (P≥0.58). The glycerol effect was not significant (P≥0.03) at all times on d 1 and tended to be significant (P=0.07) during the first 4h on d 7 and 13, but was not significant (P≥0.10; SEM = 0.26 to 0.11) over the 8-h periods. Overall, treatment effect tended to be significant (P=0.08) and effects of day and the interaction of treatment×day were not (P≥0.21). For BUN, the glucagon plus glycerol effect was significant (P≤0.05) at the first 4h and entire 8-h period on d 1. A tendency for glucagon plus glycerol started at 30min (P=0.08) and a significant effect started at 80min (P=0.04). Glucagon plus glycerol was not significant (P≥0.19; SEM = 0.26 to 0.10) at any time on d 7 and 13 postpartum. Overall, effects of treatment and day were not significant (P≥0.20) and effect of the interaction of treatment×day was (P=0.05). For TAG, glucagon effect was not significant (P=0.16). Effect of glycerol was significant (P=0.04; SEM = 0.35 to 0.55) during the first 4h on d 1 postpartum only. Specifically, the glycerol effect was significant at 45, 800, and 180min (P=0.03, P=0.04, and P=0.05, respectively). Glycerol also tended to increase plasma TAG at 30, 100, and 150min (P=0.07, P=0.08, and P=0.06) on d 1 postpartum. No effect (P≥0.43; SEM = 0.35 to 0.55) of glycerol was detected on d 7 and 13 postpartum. Overall, effects of treatment, day, and the interaction of treatment×day were not significant (P≥0.10). Glucagon plus glycerol effects were significant between 80 and 120min (P=0.04 and P=0.04; SEM = 0.33 to 0.43) on d 1. Glucagon plus glycerol effect also tended to be significant at 15 and 150min on d 7 (P=0.08 and P=0.07) and on d 1 postpartum, respectively. No effect (P≥0.17 and P≥0.22) of glucagon plus glycerol was detected on d 7 and 13 postpartum, respectively. Overall, the effects of treatment, day, and the interaction of treatment×day were not significant (P≥0.19).

Metabolic use of glycerol. α-GP = α-glycerolphosphate; G-3-P = glyceraldehyde-3-phosphate; F-1,6-P2 = fructose-1,6-bisphos-phate; F-6-P = fructose-6-phosphate; G-6-P = glucose-6-phosphate; 1,3-BPG = 1,3-bisphosphoglycerate; 3-PG = 3-phosphoglycerate; 2-PG = 2-phosphoglycerate; PEP = phosphoenol pyruvate; TAG = triacylglycerol; VLDL = very low density lipoprotein.