33 Identification of How Future Climates May Impact the Reproductive Herd and What This May Mean for Nutrition

Abstract

Abstract Changes in our climate with global warming will translate to an expansion in the seasons and an increased incidence of extreme heat events, such that heat stress (HS) will become a major management issue. This poses particular challenges to the reproductive herd, as by virtue of their increased physical size and pregnancy, they are less resilient to environmental challenges. Recent work from our laboratory has quantified the performance of summer mated piglets on productivity, demonstrating that these litters are lighter at birth, have a lighter placenta weight and are more likely to be stillborn. These piglets also take longer to reach market weight and have increased carcass backfat, which can trigger market penalties. Collectively our studies demonstrate that summer conditions result in developmental abnormalities in piglets, potentially through placental insufficiency. Additionally, HS was challenging sows during the periparturient period, resulting in more stillbirths. Two subsequent climate-controlled studies quantified the effects of HS (cyclic 28 to 33 oC) during early to mid-pregnancy (d 40 to 60), when the placenta is undergoing rapid growth, as well as the effects of HS (cyclic 28 to 30 oC) in the periparturient period (d 110 of pregnancy to farrowing). In the first study, gestational HS did not influence the number or size of the piglets at mid-gestation but increased placental mass by 22% and reduced Longissimus muscle fiber hyperplasia by 16%. The apparent enlargement of the placenta at mid-gestation may reflect an adaptation to a reduction in uterine blood flow. In other species, HS is known to reduce blood flow to the splanchnic bed and reproductive tract organs, as blood is redistributed to the periphery and upper respiratory tract to augment heat dissipation. Therefore, the prioritization of placental growth by the piglet may represent an adaptation against a backdrop of insufficient nutrient supply. Whilst reductions in muscle fiber hyperplasia were associated with reduced vascularity, although it is not clear if this was a cause or effect. In the second study, the effects of periparturient HS resulted in a 30% increase in stillbirths, with surviving piglets having lower umbilical vein blood oxygen saturation and increased meconium staining. This supports the likelihood of HS restricting uterine and umbilical blood flows, resulting in increased periparturient fetal stress. Collectively these studies emphasize the challenges that climate change poses to swine production and that addressing these challenges will require a whole farm approach. In the near term, it is likely that advances in nutrition will form an important component in adjusting to a changing climate and minimize production losses.