Date Full Report Received

10/15/2018

Date Abstract Report Received

10/15/2018

Investigation

Institution:
Primary Investigator:

Heat stress (HS) is a major economic strain for the US swine industry. In terms of reproduction, seasonal infertility is associated with HS, characterized by lengthened wean-to-estrus interval (WEI), increased spontaneous abortions and increased number of rebreeds. Unfortunately, there is unlikely to be a reduction in the strain that HS imparts to the swine industry and the negative effects of HS are likely to become more severe if climate change continues as some predict and most models forecast more extreme summer conditions in US pig-producing areas. Also, genetic selection for rapid muscle growth is thought to increase pig sensitivity to HS as these animals have a higher basal metabolic rate (i.e. greater heat load). The biological explanation for seasonal infertility is poorly understood, and until such time that a thorough understanding is gained, development of mitigating strategies will remain limited. We have discovered that heat-stressed pigs have both increased circulating insulin and lipopolysaccharide (LPS) levels. We believe that higher systemic insulin and LPS detrimentally influence ovarian biological, thereby hampering reproduction. We know that HS causes increased early gestational loss, and in other species (especially work done in dairy cows) LPS causes loss of the corpus luteum from the ovary. If this happens at any stage in a pregnancy in a sow, spontaneous abortion will occur, thus one of the objectives in this project was to determine if there are effects on the corpus luteum in sows. Our second objective in this phase of the funding period was to determine if HS affects blastocyst development in sows and if supplementation with a progesterone analogue could have therapeutic value for the swine industry. Finally, we continued analysis of projects initiated in phase I of the funding period, including completing analysis on a project that investigated the effects of arginine supplementation during gestation in a production setting, since in smaller scale projects by other groups, there has been suggestion that arginine improves offspring performance.

Through the current work, we have made a number of important discoveries: 1) HS reduces the size of the corpus luteum in swine, which is potentially causative in early embryonic loss. We have also found that this smaller corpus luteum produces more progesterone, potentially as a compensatory mechanism to counteract the impacts of HS. We do not yet know the capacity of the corpus luteum to sustain this progesterone production. 2) Progesterone analogue supplementation may be therapeutic value in combating HS effects on the CL and the developing blastocyst. 3) Arginine supplementation has moderate benefits in a large scale production setting in improving offspring performance. These findings translate to the swine industry in that we are confirming mechanisms that are or are not of value to the industry in improving swine reproductive performance. Importantly, through this funding period, we have continued to train both undergraduate and graduate students in the area of sow mortality and the impacts of abiotic stress on the pig. Three students have graduated whose theses and dissertation were focused on projects described herein and are currently working in the swine industry, academia with a swine industry extension appointment and pursuing a Ph.D. in Reproductive Biology.

Producer take-home messages:
• HS alters the corpus luteum in swine that could be the cause of early embryonic loss in sows.

• There is potential for progesterone supplementation during early embryonic development in counteracting the negative effects of HS.

• Arginine supplementation in a large scale production setting had moderate benefit in improving offspring performance.