Nano-chromium picolinate and heat stress enhance insulin sensitivity in cross-bred sheep

This study evaluated the effects of heat stress(HS)and dietary nano chromium picolinate(nCrPic)on metabolic responses of sheep to an intravenous glucose tolerance test(IVGTT),an intravenous insulin tolerance test(ITT)and an intramuscular adrenocorticotropin hormone(ACTH)challenge in sheep.Thirty-six sheep housed in metabolic cages were randomly allocated within 3 dietary groups(0,400 and 800 mg/kg supplemental nCrPic)to either thermoneutral(22℃)or cyclic HS(22 to 40℃)conditions for 3 wk.Basal plasma glucose tended to be increased during HS(P=0.052)and decreased by dietary nCrPic(P=0.013)while plasma non-esterified fatty acid concentrations were decreased(P=0.010)by HS.Di-etary nCrPic reduced the plasma glucose area under the curve(P=0.012)while there were no significant effects of HS on plasma glucose area under the curve in response to the IVGTT.The plasma insulin response over the first 60 min after the IVGTT was decreased by HS(P=0.013)and dietary nCrPic(P=0.022)with the effects being additive.In response to the ITT plasma glucose reached a nadir sooner(P=0.005)in sheep exposed to HS,although there was no effect on the depth of the nadir.Dietary nCrPic decreased(P=0.007)the plasma glucose nadir after ITT.Over the duration of the ITT plasma insulin concentrations were lower in sheep exposed to HS(P=0.013)whereas there was no significant effect of supplemental nCrPic.There was no effect of either HS or nCrPic on cortisol response to ACTH.Dietary nCrPic supple-mentation decreased(P=0.013)mitogen-activated protein kinase-8(JNK)and increased(P=0.050)carnitine palmitoyltransferase 1B(CPT1B)mRNA expression in skeletal muscle.Results of this experiment demonstrated that animals under HS and supplemented with nCrPic had greater insulin sensitivity.

Dietary nano chromium picolinate can ameliorate some of the impacts of heat stress in cross-bred sheep

Two studies were conducted to evaluate the effect of nano chromium picolinate(nCrPic)during heat stress(HS)in sheep.In the initial study,36 Merino×Poll cross-bred sheep were individually penned and allocated to 3 dietary treatments(0,400 and 800μg/kg nCrPic)for 8 wk.Body composition was determined at the beginning and end of the experiment using dual energy X-ray absorptiometry.The sheep remained in their dietary groups but were then placed in metabolic cages and randomly allocated within the dietary group to differing ambient temperature regimes,i.e.,thermo-neutral(TN)(n=18)and HS(n=18),for 3 wk.Dietary nCrPic had no effect on growth performance and body composition during the initial study conducted under TN conditions.Heat stress decreased average daily feed intake(ADFI)(P=0.002)whereas sheep under HS had reduced average daily gain(ADG)and indeed lost weight(P<0.001).Dietary nCrPic increased both ADFI(P=0.041)and ADG(P=0.049)under both TH and HS conditions such that the performance of sheep receiving supplemental nCrPic and exposed to HS was similar to that of control sheep maintained under TN conditions.Heat stress increased rectal temperature(P<0.001)and respiration rate(P<0.001),particularly during the hottest parts of the day as indicated by interactions(P<0.001)between time of day and thermal treatment.Rectal temperature was lower in sheep fed nCrPic(P=0.050),particularly under peak HS conditions during the afternoon as indicated by the interactions between dietary nCrPic and time of day(P<0.001)and dietary nCrPic,thermal treat-ment and time of day(P=0.010).Similarly,respiration rate was lower in sheep fed nCrPic under peak HS conditions during the afternoon as indicated by the interactions between dietary nCrPic and thermal treatment(P<0.001)and dietary nCrPic and time of day(P=0.030).In conclusion,dietary nCrPic can partially ameliorate the negative effects of HS as indicated by the maintenance of ADFI and decreased physiological responses,such as elevations in rectal temperature and respiration rate.