survey of different responses of non-pregnant fat-tailed ewes to the intravenous glucose tolerance test during the feed restriction period

Introduction: blood glucose concentration varies according to the physiological stages and daily milk yield. in ruminants, the gluconeogenesis process supplies most of the glucose requirements, which plays a prominent role in the metabolism and maintaining energy homeostasis. due to thepivotal role of glucose and its metabolic processes in ruminants, particularly in milk production andoptimizing reproductive efficiency, comprehensive studies have been conducted on dairy cows. theglucose tolerance test (ivgtt) is one of the techniques to assess glucose metabolism and the capacityof various tissues to react over insulin secretion (kaneko et al. 2008). although ivgtt studies haveachieved significant success in glucose and insulin metabolism, the effect of some factors, such asfeed restriction, physiological status, and dose of glucose infusion, need to be sufficiently clarified.the published results demonstrated that feed restriction at 65% of diet energy density increases theplasma glucose concentration in non-pregnant ewes (zarrin et al. 2021b). this study evaluated theeffect of intravenous glucose infusion on blood metabolite and insulin concentration in non-pregnantfat-tailed ewes during feed restriction.materials and methods: ten multiparous non-pregnant fat-tailed turki-qashqai ewes (3-4 years oldand 49.2 ± 3.60 kg body weight), after two weeks of adaptation, were randomly allocated into twotreatment groups: the control group (control; n =5) and the feed restriction group (restriction; n =5).the control ewes had free access to feed throughout the experiment (weeks 1 to 5). the restrictedewes received a diet equivalent to 100, 50, 65, 80, and 100% of the energy content of the diet at weeks1, 2, 3, 4, and 5 relative to the start of the experiment (ding et al. 2016). intravenous glucose infusion(1 ml/kg bw) was administered in the third week of the experiment. blood samples were taken 10and 5 minutes before and 2, 5, 10, 15, 20, 25, 30, 45, 60, 75, 90, 105, 120, and 180 minutes after theinfusion. the area under the curve (auc) was calculated for each parameter during the ivgtt (0-180 min) using the trapezoidal roll (sum of the rectangular and triangular areas under the curve). therevised quantitative insulin sensitivity check index (rquicki) was calculated using the proposed equation (holtenius and holtenius, 2007). for the calculation of the glucose clearance rate (the rateat which the concentration of glucose is removed from the blood, k (%/min)) and the half-life ofglucose (t1/2; the time required to reduce the concentration of glucose by half), were calculated bykaneko et al.(2008). data was analyzed by the mixed procedure of sas. treatments (control andrestriction), time points (0-180 min), and the interactions (treatment × time) were considered as fixed effects. the animal breed was considered as random effect. measured data were considered asdependent variables. the data obtained for ivgtt parameters were evaluated using the sas glmprocedure. the results from reference samples were included in the model as covariates for individualdifferences between ewes. data are presented as means ± sem and differences were consideredsignificant if p ≤ 0.05. results and discussion: glucose infusion increased glucose concentration in both groups (p<0.01).no significant changes were observed for glucose turnover, half-life, and the area under the glucosecurve between the groups. insulin concentration increased in both groups a few minutes after glucoseinfusion, but the increase was slighter in restriction (p<0.05). free fatty acids declined due tointravenous glucose infusion in control (p<0.05). glucose infusion did not affect betahydroxybutyrateconcentration. the current study was designed and conducted to study the glucose clearance pattern during feed restriction regardless of the many potentially confounding effects of the pregnancy presented in other studies.

survey of different responses of non-pregnant fat-tailed ewes to the intravenous glucose tolerance test during the feed restriction period

introduction: blood glucose concentration varies according to the physiological stages and daily milk yield. in ruminants, the gluconeogenesis process supplies most of the glucose requirements, which plays a prominent role in the metabolism and maintaining energy homeostasis. due to thepivotal role of glucose and its metabolic processes in ruminants, particularly in milk production andoptimizing reproductive efficiency, comprehensive studies have been conducted on dairy cows. theglucose tolerance test (ivgtt) is one of the techniques to assess glucose metabolism and the capacityof various tissues to react over insulin secretion (kaneko et al. 2008). although ivgtt studies haveachieved significant success in glucose and insulin metabolism, the effect of some factors, such asfeed restriction, physiological status, and dose of glucose infusion, need to be sufficiently clarified.the published results demonstrated that feed restriction at 65% of diet energy density increases theplasma glucose concentration in non-pregnant ewes (zarrin et al. 2021b). this study evaluated theeffect of intravenous glucose infusion on blood metabolite and insulin concentration in non-pregnantfat-tailed ewes during feed restriction.materials and methods: ten multiparous non-pregnant fat-tailed turki-qashqai ewes (3-4 years oldand 49.2 ± 3.60 kg body weight), after two weeks of adaptation, were randomly allocated into twotreatment groups: the control group (control; n =5) and the feed restriction group (restriction; n =5).the control ewes had free access to feed throughout the experiment (weeks 1 to 5). the restrictedewes received a diet equivalent to 100, 50, 65, 80, and 100% of the energy content of the diet at weeks1, 2, 3, 4, and 5 relative to the start of the experiment (ding et al. 2016). intravenous glucose infusion(1 ml/kg bw) was administered in the third week of the experiment. blood samples were taken 10and 5 minutes before and 2, 5, 10, 15, 20, 25, 30, 45, 60, 75, 90, 105, 120, and 180 minutes after theinfusion. the area under the curve (auc) was calculated for each parameter during the ivgtt (0-180 min) using the trapezoidal roll (sum of the rectangular and triangular areas under the curve). therevised quantitative insulin sensitivity check index (rquicki) was calculated using the proposed equation (holtenius and holtenius, 2007). for the calculation of the glucose clearance rate (the rateat which the concentration of glucose is removed from the blood, k (%/min)) and the half-life ofglucose (t1/2; the time required to reduce the concentration of glucose by half), were calculated bykaneko et al.(2008). data was analyzed by the mixed procedure of sas. treatments (control andrestriction), time points (0-180 min), and the interactions (treatment × time) were considered as fixed effects. the animal breed was considered as random effect. measured data were considered asdependent variables. the data obtained for ivgtt parameters were evaluated using the sas glmprocedure. the results from reference samples were included in the model as covariates for individualdifferences between ewes. data are presented as means ± sem and differences were consideredsignificant if p ≤ 0.05. results and discussion: glucose infusion increased glucose concentration in both groups (p<0.01).no significant changes were observed for glucose turnover, half-life, and the area under the glucosecurve between the groups. insulin concentration increased in both groups a few minutes after glucoseinfusion, but the increase was slighter in restriction (p<0.05). free fatty acids declined due tointravenous glucose infusion in control (p<0.05). glucose infusion did not affect betahydroxybutyrateconcentration. the current study was designed and conducted to study the glucose clearance pattern during feed restriction regardless of the many potentially confounding effects of the pregnancy presented in other studies.