Gestational heat stress alters skeletal muscle gene expression profiles and vascularity in fetal pigs in a sexually dimorphic manner

Background: There is evidence that sow heat stress(HS) during gestation affects fetal development with implications for impaired muscle growth. We have previously demonstrated that maternal HS during early to midgestation compromised muscle fibre hyperplasia in developing fetal pigs. Thus, we hypothesised these phenotypic changes are associated with a change in expression of genes regulating fetal skeletal muscle development and metabolism. To test this, at d 60 of gestation, RNA sequencing and immunohistochemistry were performed on fetal longissimus dorsi(LD) muscle biopsies collected from pregnant gilts that had experienced either thermoneutral control(CON, 20 ℃, n = 7 gilts, 18 LD samples) or controlled HS(cyclic 28 to 33 ℃, n = 8 gilts, 23 LD samples)conditions for 3 weeks.Results: A total of 282 genes were differentially expressed between the HS and CON groups in female LD muscles(false discovery rate(FDR) ≤ 0.05), whereas no differentially expressed genes were detected in male LD muscles between the two groups(FDR > 0.05). Gestational HS increased the expression of genes associated with transcription corepressor activity, adipogenesis cascades, negative regulation of angiogenesis and pro-inflammatory signalling in female LD muscles. Immunohistochemical analyses revealed a decreased muscle vascularity density in fetuses from HS group for both sexes compared to those from the CON group(P = 0.004).Conclusions: These results reveal gilt HS during early to mid-gestation altered gene expression profiles in fetal LD muscles in a sexually dimorphic manner. The molecular responses, including transcription and angiogenesis repressions and enhanced adipogenesis cascades, were exclusively observed in females. However, the associated reductions in muscle vascularity were observed independently of sexes. Collectively this may indicate female fetal pigs are more adaptive to gestational HS in terms of gene expression changes, and/or there may be sexually dimorphic differences with respect to the timing of muscle molecular responses to gestational HS.

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.

Acid-insoluble ash is a better indigestible marker than chromic oxide to measure apparent total tract digestibility in pigs

The aim of this study was to determine the apparent total tract digestibility(ATTD)of nutrients in cottonseed meal(CSM)and soybean meal(SBM)in simple carbohydrate and more complex wheat-based diets using 2 indigestible markers and total faecal collection.Twenty-five Large White×Landrace boars(57.8 kg)were randomly allocated to either a pure wheat diet,40%CSM or SBM in either a sugar-starch-(1∶1)or wheat-based diet for 18 d.Acid-insoluble ash(AIA)and chromic oxide(Cr2O3)were included in all diets as indigestible markers.Diets were offered(1,800 g/d per pig)in 3 meals/d from d 1 to 11 and 8 meals/d from d 12 to 17.On d 9,the pigs were moved to individual metabolism cages to allow total faecal collection.On d 18,the pigs were fed hourly for 8 h.After the 8th meal,pigs were anaesthetized and digesta sampled from the terminal ileum and rectum before lethal injection.There were no differences between ATTD of nitrogen(N)determined using AIA as a marker and measured by total faecal collection.On the other hand,the ATrD of N of diets containing CSM in sugar-starch-or wheat-based diets and the pure wheat diet determined using Cr2O3 as a marker was less(-3.11%,-4.46%and-6.59%;P<O.001)than that measured by total faecal collection.The ATTD of N determined using AIA as a marker was highly correlated with that measured using total faecal collection(P<0.001;R2=0.95).Similarly,the ATTD of N determined using Cr2O3 as a marker was correlated with that measured using total faecal collection,although the correlation was not quite as strong as using AIA(P<0.001;R2=0.87).Also,the slope of the regression line and the intercept were closer to unity and zero for the relationship when the ATTD of N was determined using AIA compared to Cr2O3 as an indigestible marker.The ATTD of organic and dry matter behaved similarly.These data demonstrate that the basal diet and choice of indigestible marker can substantially influence the ATTD and that the use of AIA as an indigestible marker is more suitable than Cr2O3 in digestibility studies in pigs.

Basal diet and indigestible marker influence apparent digestibilities of nitrogen and amino acids of cottonseed meal and soybean meal in pigs

This study was to determine the apparent ileal nitrogen(N)and amino acid digestibilities of cottonseed meal(CSM)and soybean meal(SBM)in simple carbohydrate-based and more complex wheat-based diets.Twenty five Large White × Landrace boars(40.9 kg)were randomly allocated to one of 5 dietary treatments:a wheat diet,40% CSM in either a sugar:starch(1:1)or wheat-based diet,or 40% SBM in either a sugar:starch or wheat-based diet for 14 d.All diets contained vitamins,minerals,and contained acid-insoluble ash(AIA)and Cr2 O3 as indigestible markers.Rations were offered(1,800 g/pig per d)in3 meals/d on d 1-11 and 8 meals/d on d 12-13.On d 14,the pigs were fed hourly for 8 h.After the 8 th meal,pigs were anaesthetised with isoflurothane,and ileal and faecal digesta sampled from the terminal ileum and rectum before lethal injection of barbiturate.Apparent ileal digestibility(AID)of N was greater(12.1%)when CSM was fed in the wheat-based diet as compared to the simple carbohydrate-based diet,whereas apparent ileal N digestibility of SBM was slightly lower(-4.5%)in the wheat-based diet as compared to the sugar:starch-based diet.Apparent ileal amino acid digestibility generally respondeds similarly to N.Therefore,while there was a wide difference in apparent N and amino acid digestibilities of SBM and CSM when they were fed in the sugar:starch-based diets,these differences were less apparent when they were fed the wheat-based diet.There was an apparent net release of N into the hindgut of pigs fed CSM in both base diets.Conversely,there was quite substantial apparent digestion of N in the hindgut of pigs fed SBM in both base diets.The use of Cr2 O3 as an indigestible marker resulted in lower apparent ileal and faecal digestibilities than using AIA,particularly for diets containing CSM.These data demonstrate that the basal diet and choice of indigestible marker can substantially influence the estimate of apparent N digestibility,this response can differ for different protein meals.

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.