Heat stress effects on livestock: molecular,cellular and metabolic aspects,a review

Elevated ambient temperatures affect animal production and welfare. Animal's reduced production performances during heat stress were traditionally thought to result from the decreased feed intake. However, it has recently been shown that heat stress disturbs the steady state concentrations of free radicals, resulting in both cellular and mitochondrial oxidative damage. Indeed, heat stress reorganizes the use of the body resources including fat, protein and energy. Heat stress reduces the metabolic rates and alters post‐absorptive metabolism, regardless of the decreased feed intake. Consequently, growth, production, reproduction and health are not priorities any more in the metabolism of heat‐stressed animals. The drastic effects of heat stress depend on its duration and severity. This review clearly describes about biochemical, cellular and metabolic changes that occur during thermal stress in farm animals.     

The protective effect of γ‐aminobutyric acid on the development of immune function in chickens under heat stress

This study aimed to investigate the protective effect of γ‐aminobutyric acid (GABA) on the development of immune function in chicks under heat stress (HS). One‐day‐old male Wenchang chicks were randomly divided into control (CK), HS and GABA+HS groups. The GABA+HS group was fed with 0.2 ml GABA solution (50 mg/kg) daily by oral gavage. The HS and GABA+HS groups were placed in 40 ± 0.5 °C environment for 2 h heat treatment from 13:00 each day. Blood samples were routinely taken at 14, 21, 28, 35 and 42 days respectively, and the contents of T and B lymphocyte subsets in the blood and tissue were analysed by flow cytometry after FITC/PE double staining; the plasma levels of interleukin (IL)‐2, immunoglobulin (Ig)A, IgG and IgM were determined using ELISA. The thymus and the bursa of fabricius were also collected to analyse for organ index and observe for the changes in tissue microstructure. In addition, the chicks received primary and secondary immunizations with attenuated Newcastle disease (ND) vaccine (LaSota strain) at 7 and 28 days respectively; conventional hemagglutination inhibition (HI) assay was performed to monitor the titre changes in plasma antibody against ND virus in the birds. Our results indicated that the indices of both thymus and bursa of fabricius, the intactness of tissue structure and development, the plasma levels of IL‐2, IgA, IgG and IgM, the titres of ND antibody, and the levels of B and T lymphocyte subsets in HS group were all significantly lower than those in CK group (p < 0.05). However, all above indices were significantly improved in GABA+HS group compared with those in HS group (p < 0.05). These results demonstrated that while HS seriously affected the development of immune function in Wenchang chicks, GABA effectively alleviated the damages of HS to the development of immune function in chicks.     

Tissue responses to fractional transient heating with sinusoidal heat flux condition on skin surface

A fractional model of Bioheat equation for describing quantitatively the thermal responses of skin tissue under sinusoidal heat flux conditions on skin surface is given. Laplace transform technique is used to obtain the solution in a closed form. The resulting formulation is applied to one‐dimensional application to investigate the temperature distribution in skin with instantaneous surface heating for different cases. According to the numerical results and its graphs, conclusion about the fractional bioheat transfer equation has been constructed. Sensitivity analysis is performed to explore the thermal effects of various control parameters on tissue temperature. The comparisons are made with the results obtained in the case of the absence of time‐fractional order. © 2016 Japanese Society of Animal Science     

马立克病肿瘤组织内HSP60表达及生物学作用初步研究

本试验旨在研究HSP60与马立克病肿瘤发生、发展之间的相关性。通过人工感染,建立鸡马立克病肿瘤模型,定期剖杀,利用病理组织学和免疫组织化学方法,检测HSP60与肿瘤细胞定位之间的相关性;设计HSP60 RNA干扰序列,构建重组慢病毒,转染MSB-1细胞,利用流式细胞技术,探索降低HSP60转录表达对MSB-1细胞凋亡水平的影响。结果显示：HSP60在肿瘤细胞的细胞质内强表达;成功构建了HSP60 RNA干扰慢病毒,且5147序列干扰效果最佳;5147序列慢病毒转染48 h时,与对照序列组和空白对照组相比,HSP60转录、表达水平极显著降低（P<0.01）,MSB-1细胞凋亡水平极显著升高（P<0.01）。在马立克病肿瘤发生、发展过程中,HSP60组织细胞定位与肿瘤细胞具有明显的相关性,降低HSP60表达水平能够导致MSB-1细胞凋亡升高,说明HSP60对肿瘤细胞的存活具有重要的生物学作用。     

Comparative study of stress response,growth and development of uteri in post‐weaning gilts challenged with zearalenone and estradiol benzoate

The objective of this study was to evaluate the effects of zearalenone (ZEA) and estradiol benzoate (EB) on stress injury and uterine development in post‐weaning gilts. Thirty healthy post‐weaning female gilts (Duroc × Landrace × Large White) aged 28–32 days were randomly allocated to three treatments as follows: (a) basal diet (Control), (b) basal diet plus 1.0 mg/kg purified ZEA (ZEA) and (c) basal diet plus 0.75 ml (1.5 mg) EB per pig at 3‐days intervals by intramuscular injection (EB). The serum estradiol (E₂), the final and the increased vulvar area, uterine index, thickness of the myometrium and endometrium, and protein expression of heat shock protein 70 (HSP70) in ZEA group were higher than those in the control group (p < .05), but lower than those in the EB group (p < .05). The serum luteinizing hormone in ZEA group was lower than that of the control group (p < .05), but higher than that in the EB group (p < .05). Higher serum follicle‐stimulating hormone and progesterone were observed in the ZEA and control groups than those in the EB group (p < .05). The serum glutathione peroxidase activity in the ZEA group was lower than that in the control and EB groups (p < .001), and the malondialdehyde in the ZEA group was higher than that in the control and EB groups (p < .001). Moreover, the relative mRNA and protein expression of growth hormone receptor (GHR) and relative mRNA expression of HSP70 in the ZEA and EB groups were higher than those in the control group (p < .05). In conclusion, both ZEA (1.0 mg/kg) and EB (1.5 mg at 3 days intervals by intramuscular injection) stimulated vulvar swelling and uterine hypertrophy by disordering serum hormones and up‐regulating GHR expression, and induced stress by different mechanisms in this study. Furthermore, the observed up‐regulating HSP70 expression challenged by ZEA or EB may be part of the mechanism to resist stress injury.     

Impact of diet composition and temperature–humidity index on water and dry matter intake of high‐yielding dairy cows

The temperature–humidity index (THI) is widely used to characterize heat stress in dairy cattle. Diet composition is known to induce variation in metabolic‐associated heat production. However, the relationships between THI and diet are poorly characterized with regard to performance and intake behaviour. Therefore, the objectives were to evaluate the impact of THI on water intake (WI), dry matter intake (DMI) and the frequency of drinking and feeding bouts in lactating dairy cows offered four dietary treatments: each contained 20% grass silage and additionally (i) 20% maize silage, 60% concentrate (M‐HC); (ii) 60% maize silage, 20% concentrate (M‐LC); (iii) 20% pressed beet pulp silage, 60% concentrate (BPS‐HC); or (iv) 60% pressed beet pulp silage, 20% concentrate (BPS‐LC) (DM basis). Individual WI and DMI were recorded from April to July 2013. Furthermore, dietary effects on milk production and reticular pH were estimated. Milk yield was lowest for M‐LC, while energy‐corrected milk was similar for all diets. Milk fat percentage was higher and milk protein amount lower for cows offered both LC diets. Reticular pH below 6.3, 6.0 and 5.8 lasted longest for BPS‐LC. WI was higher for HC diets. However, the frequency of drinking bouts was not influenced by the ration. Lower DMI occurred for BPS‐LC compared to M‐LC. Frequency of feeding bouts was significantly higher for LC diets. THI was significantly related to WI, DMI as well as drinking and feeding bouts. Per increasing THI, WI increased slightly more for LC diets and DMI decreased more for HC diets. Frequency of drinking bouts increased slightly higher for BPS rations per rising THI, while the decrease in feeding bouts was highest for M‐HC. In conclusion, TMR composition and moderate heat stress impacted WI and DMI of dairy cows, while both dietary energy density and ruminal filling might intensify the THI impact.     

Effects of a short‐term supranutritional selenium supplementation on redox balance,physiology and insulin‐related metabolism in heat‐stressed pigs

Heat stress (HS) disrupts redox balance and insulin‐related metabolism. Supplementation with supranutritional amounts of selenium (Se) may enhance glutathione peroxidase (GPX) activity and reduce oxidative stress, but may trigger insulin resistance. Therefore, the aim of this experiment was to investigate the effects of a short‐term high Se supplementation on physiology, oxidative stress and insulin‐related metabolism in heat‐stressed pigs. Twenty‐four gilts were fed either a control (0.20 ppm Se) or a high Se (1.0 ppm Se yeast, HiSe) diet for 2 weeks. Pigs were then housed in thermoneutral (20°C) or HS (35°C) conditions for 8 days. Blood samples were collected to study blood Se and oxidative stress markers. An oral glucose tolerance test (OGTT) was conducted on day 8 of thermal exposure. The HS conditions increased rectal temperature and respiration rate (both p < .001). The HiSe diet increased blood Se by 12% (p < .05) and ameliorated the increase in rectal temperature (p < .05). Heat stress increased oxidative stress as evidenced by a 48% increase in plasma advanced oxidized protein products (AOPPs; p < .05), which may be associated with the reductions in plasma biological antioxidant potential (BAP) and erythrocyte GPX activity (both p < .05). The HiSe diet did not alleviate the reduction in plasma BAP or increase in AOPPs observed during HS, although it tended to increase erythrocyte GPX activity by 13% (p = .068). Without affecting insulin, HS attenuated lipid mobilization, as evidenced by a lower fasting NEFA concentration (p < .05), which was not mitigated by the HiSe diet. The HiSe diet increased insulin AUC, suggesting it potentiated insulin resistance, although this only occurred under TN conditions (p = .066). In summary, HS induced oxidative stress and attenuated lipid mobilization in pigs. The short‐term supranutritional Se supplementation alleviated hyperthermia, but did not protect against oxidative stress in heat‐stressed pigs.     

Effects of Chinese herbal medicine and cold exposure on plasma glucose,leucine and energy metabolism in sheep

An experiment was carried out to assess the feeding effect of Chinese herbal medicine on N balance, ruminal fermentation characteristics, kinetics of plasma glucose, leucine and energy metabolism in sheep kept at thermoneutral environment (23°C) or exposed to cold (2–4°C). Four sheep were subjected to either mixed hay (MH‐diet) or hay supplemented with 2% of a traditional nourishing Chinese herbal medicine mixture (Astragalus root, Angelica root and Atractylodes rhizome; CHM‐diet) over two 23‐day periods using a crossover design. Cold exposure was conducted for 5 days. The isotope dilution of [U‐¹³C]glucose with open circuit calorimetry was used to determine the turnover and oxidation rates of plasma glucose and metabolic heat production. The rate of plasma leucine turnover was measured with an isotope dilution method using [1‐¹³C]leucine. N intake was higher, N excretion through faeces was lower and N digestibility was higher for the CHM‐diet than the MH‐diet. Rumen pH was lower, concentration of rumen NH₃ was higher, concentrations of rumen total VFA and acetate tended to be higher and propionate was higher for the CHM‐diet compared with the MH‐diet. Turnover rate of plasma glucose was higher for the CHM‐diet than the MH‐diet and increased during cold exposure. Oxidation rate of plasma glucose did not differ between diets and also between environments. Turnover rate of plasma leucine was higher for the CHM‐diet compared with the MH‐diet but remained similar between environments. Heat production was greater for the CHM‐diet than the MH‐diet and increased during cold exposure. No significant diet × environment interaction was detected. The present results demonstrated that plasma glucose and energy metabolism were enhanced by both Chinese herbal medicine and cold exposure; plasma leucine metabolism was enhanced by Chinese herbal medicine but with lack of change in response to cold exposure in sheep under the conditions of the current experiment.