New Findings: What is the central question of this study? Oxidative stress may play a role in compromising intestinal epithelial barrier integrity in pigs subjected to heat stress, but it is unknown whether an increase of dietary antioxidants (selenium and vitamin E) could alleviate gut leakiness in heat‐stressed pigs. What is the main finding and its importance? Levels of dietary selenium (1.0 p.p.m.) and vitamin E (200 IU kg⁻¹) greater than those usually recommended for pigs reduced intestinal leakiness caused by heat stress. This finding suggests that oxidative stress plays a role in compromising intestinal epithelial barrier integrity in heat‐stressed pigs and also provides a nutritional strategy for mitigating these effects. Heat stress compromises the intestinal epithelial barrier integrity of mammals through mechanisms that may include oxidative stress. Our objective was to test whether dietary supplementation with antioxidants, selenium (Se) and vitamin E (VE), protects intestinal epithelial barrier integrity in heat‐stressed pigs. Female growing pigs (n = 48) were randomly assigned to four diets containing from 0.2 p.p.m. Se and 17 IU kg⁻¹ VE (control, National Research Council recommended) to 1.0 p.p.m. Se and 200 IU kg⁻¹ VE for 14 days. Six pigs from each dietary treatment were then exposed to either thermoneutral (20°C) or heat‐stress conditions (35°C 09.00–17.00 h and 28°C overnight) for 2 days. Transepithelial electrical resistance and fluorescein isothiocyanate–dextran (4 kDa; FD4) permeability were measured in isolated jejunum and ileum using Ussing chambers. Rectal temperature, respiratory rate and intestinal HSP70 mRNA abundance increased (all P < 0.001), and respiratory alkalosis occurred, suggesting that pigs were heat stressed. Heat stress also increased FD4 permeability and decreased transepithelial electrical resistance (both P < 0.01). These changes were associated with changes indicative of oxidative stress, a decreased glutathione peroxidase (GPX) activity and an increased glutathione disulfide (GSSG)‐to‐glutathione (GSH) ratio (both P < 0.05). With increasing dosage of Se and VE, GPX‐2 mRNA (P = 0.003) and GPX activity (P = 0.049) increased linearly, the GSSG:GSH ratio decreased linearly (P = 0.037), and the impacts of heat stress on intestinal barrier function were reduced (P < 0.05 for both transepithelial electrical resistance and FD4 permeability). In conclusion, in pigs an increase of dietary Se and VE mitigated the impacts of heat stress on intestinal barrier integrity, associated with a reduction in oxidative stress.

The global population is predicted to grow to over 9 billion by the middle of 21st century, with 70% of people living in urban areas, and food demand is projected to grow by 70% by 2050. Climate change presents a series of challenges for global animal agriculture. As a result of thermal challenges associated with climate variability, availability of quality pasture, animal behaviour, physiological and immunological functions are potentially impacted. Oxidative status plays an important role in the regulation and maintenance of several physiological and immunological functions of the body. Ruminants are exposed to several environmental and metabolic challenges that can trigger oxidative stress. In this scenario, it is possible for an increase in free radical production and a depletion of antioxidant reserves, resulting in damage to lipids, proteins and DNA. Since oxidative stress can affect animal health and the quality of their products (meat/milk), antioxidant supplementation of ruminant diets represents a useful tool to sustain redox homeostasis when the ruminants are exposed to oxidative stress. This paper will examine the roles that oxidative stress plays in some physiological functions, and it will discuss the implications of antioxidant supplementation on ruminant health and production. Physiological levels of dietary antioxidants underpin efficient energy utilisation, optimal antioxidant potential, and balanced mitochondrial function to enhance protein deposition without impacting animal health. The research conducted over the last decade has improved the understanding of physiological functions of antioxidants, with selenium and vitamin E receiving particular attention. There is evidence that the functions of selenium and vitamin E extend beyond the classical antioxidant properties to immunomodulation especially when administered at higher doses than recommended. Improving the oxidative status of ruminants will play an important role in delivering high-quality milk and meat products to consumers. Considering the growing awareness among consumers of the benefits of antioxidant-rich food, there is a great opportunity for the livestock industries to focus on producing antioxidant-enriched milk and meat products or functional foods. Therefore, the premise of this paper is to review the recent developments in understanding antioxidant dynamics in ruminants and their role in reducing the impact of environmental stress and metabolic diseases. In addition, the paper will explore the putative implications that antioxidant supplementation has on the quality animal products and how the improved understanding can be best utilised to achieve efficient and sustainable animal production systems to ensure quality animal products for human consumption.

Pigs are comparatively less heat tolerant than other species of production animals, which poses challenges for stock productivity and management during seasonal heat waves that occur in summer. The issues surrounding heat and pig production are predicted to increase, based on the actions of climate change increasing the intensity, frequency and duration of heat waves. Furthermore, future growth areas of pig production are going to be in tropical regions such as South-east Asia and Latin America. Efforts by the pig to dissipate excess body heat come at a cost to health and divert energy away from growth, compromising efficient pig production. Management of heat stress requires multiple strategies, and recent research is improving the understanding of the application of nutritional strategies to ameliorate the effects of heat stress. In particular the use of feed additives is an important, flexible and economical method to alleviate heat stress and the intensive nature of pig production lends itself to the use of additives. Some specific examples include antioxidants, betaine and chromium, which have been proved effective or being tested in mitigating some certain impacts of heat stress in pigs. The aim of this review is to summarise recent advances in the nutritional management of heat stress in pigs.

Pig production faces seasonal fluctuations. The low farrowing rate of sows mated in summer, increased carcass fatness of progeny born to the sows mated in summer, and slower growth rate of finisher pigs in summer are three economically important impacts identified in the pig industry. The purpose of this review is to examine advances over the past decade in understanding the mechanisms underlying the three impacts associated with summer conditions, particularly heat stress (HS), and to provide possible amelioration strategies. For impact 1, summer mating results in low farrowing rates mainly caused by the high frequency of early pregnancy disruptions. The contributions of semen DNA damage, poor oocyte quality, local progesterone concentrations, and suboptimal embryonic oestrogen secretion are discussed, as these all may contribute to HS-mediated effects around conception. Despite this, it is still unclear what the underlying mechanisms might be and thus, there is currently a lack of commercially viable solutions. For impact 2, there have been recent advances in the understanding of gestational HS on both the sow and foetus, with gestational HS implicated in decreased foetal muscle fibre number, a greater proportion of lighter piglets, and increased carcass fatness at slaughter. So far, no effective strategies have been developed to mitigate the impacts associated with gestational HS on foetuses. For impact 3, the slowed growth rate of pigs during summer is one reason for the reduced carcass weights in summer. Studies have shown that the reduction in growth rates may be due to more than reductions in feed intake alone, and the impaired intestinal barrier function and inflammatory response may also play a role. In addition, it is consistently reported that HS attenuates fat mobilisation which can potentially exacerbate carcass fatness when carcass weight is increased. Novel feed additives have exhibited the potential to reduce the impacts of HS on intestinal barrier function in grower pigs. Collectively, based on these three impacts, the economic loss associated with HS can be estimated. A review of these impacts is warranted to better align the future research directions with the needs of the pig industry. Ultimately, a better understanding of the underlying mechanisms and continuous investments in developing commercially viable strategies to combat HS will benefit the pig industry.

It is known that pig offspring born from pregnant pigs exposed to elevated ambient temperatures during gestation have altered phenotypes, possibly due to placental insufficiency and impaired fetal growth. Therefore, the objective of this study was to quantify the effect of maternal heat exposure during early-mid gestation, when pig placentae grow heavily, on placental and fetal development. Fifteen pregnant pigs were allocated to thermoneutral (TN; 20 °C; n = 7) or cyclic elevated temperature conditions (ET; 28 to 33 °C; n = 8) from d40 to d60 of gestation. Following euthanasia of the pigs on d60, placental and fetal morphometry and biochemistry were measured. Compared to TN fetuses, ET fetuses had increased (P = 0.041) placental weights and a lower (P = 0.013) placental efficiency (fetal/placental weight), although fetal weights were not significantly different. Fetuses from ET pigs had reduced (P = 0.032) M. longissimus fibre number density and a thicker (P = 0.017) placental epithelial layer compared to their TN counterparts. Elevated temperatures decreased (P = 0.026) placental mRNA expression of a glucose transporter (GLUT-3) and increased (P = 0.037) placental IGF-2 mRNA expression. In conclusion, controlled elevated temperatures between d40 to d60 of gestation reduced pig placental efficiency, resulting in compensatory growth of the placentae to maintain fetal development. Placental insufficiency during early-mid gestation may have implications for fetal development, possibly causing a long-term phenotypic change of the progeny.